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Porting the Chinese 48cc HT engine

this information is really cool, is from http://www.dragonfly75.com/:

I use Jaaps Puch calculator (in Dutch which is downloadable to your Windows computer) after measuring port heights, or use a degree wheel to figure out the port timings in degrees. Go to the bottom of this page for the translations to English if you want to use the Puch Calculator. Or click here to go to a good on-line calculator. (Use 38 for stroke, 85 for conrod, .8 for "deck").

There's two ways to describe the port timing of each port. One, the most common, is to describe the total amount of crank degrees the port is open during one crank rotation. The second way is to tell at what crank degrees, in relation to zero degrees (piston top dead center), the port begins to open. From top dead center to bottom dead center, one half rotation, is 180 degrees. So if the exhaust port opens at 110 ATDC (after top dead center) then to get the total open port duration you'd subtract 110 from 180 and multiply by two. So 180-110=70. 70x2=140. 110°ATDC is 140° duration. If the intake port of a piston port engine (like the Grubee) opens around 60°BTDC (before top dead center) then you can figure the duration just by multiplying by two. That would equal 120° duration. For changing any port, more duration is for higher rpm power and less duration befits lower rpm power.

Standard 48cc : 141° exhaust duration (28mm from top of cylinder), 111° transfer duration (32mm), 112° intake duration (55.5mm), 44.8mm piston length at intake side, .8mm deck height, 38mm stroke.

Except for the intake timing this engine is ported good for a mild low rpm power. An ideal intake timing for the standard engine is 60° BTDC (120° dur.). To get 60° just lower the bottom of the intake port to 56.7mm from the top of the cylinder (or remove 1.2mm from the bottom of the intake side of the piston skirt). Also widen the port by 4mm on each side. (See explanation later on page.) If you need more speed you can change the rear sprocket to one with less teeth or raise the exhaust port. A 10% decrease in number of teeth will result in a 10% increase in speed. But this change reduces your ability to accelerate and climb streets.

Here's how you can change the ports of the engine if you want the best all around power from it. If you don´t make .8mm piston ramps for even more low rpm power then make the distance to the transfers 31.2mm. These dimensions have been scientifically calculated to be the best for a top rpm of 7000. 

Don't port for higher rpm's unless you plan to also balance the crank. Otherwise the engine will be annoyingly vibrating above 5000 rpm and will destroy the con-rod and crank main bearings quickly. This is especially important for the larger 66/80cc engines which use a similar crank with a heavier piston that imbalances it even more.

Here is porting for the best low rpm power. It's basically the same as stock except for more intake duration and wider ports. Raise the exhaust port for more top speed if desired.

Porting can be done at home with a rotary tool that uses the common 1/8" diameter shank bits. WalMart sells a good one with 3 speeds and 1" diameter cutting wheels which can be trimmed down to smaller diameters as need be. Just be sure to not have your eyes in the path of metal bits being thrown outward away from the wheel. Accurate measurement of port heights can be done with a digital caliper, also from WalMart.

Exhaust port enlarging:
According to a free pipe design program, for low rpm power with an expansion chamber the exhaust port area needs to be no more than an equivalent 17.8mm circular diameter to match the 20mm diameter of the exhaust pipe at a 1/1.125 ratio. That means the port should be no more than 12mm high and 24mm wide (measuring with something straight from left to right edge). Raising the port ceiling 1mm from stock and widening it slightly will result in this dimension. Top to bottom port height is equal to 38.7 minus the # of millimeters the port is from the top of the cylinder. That will result in less than the measured amount because the piston doesn't quite go down to the bottom of the port. Mine, at 12x24mm, is equal to that 17.8mm diameter. Expertssay the port should not exceed 70 degrees. That equates to 24.5mm for a 48cc, and 28.1mm for a 66cc. (Those widths are not straight line, but rather the port width on paper impressed with the port edges.) Click here to read more about port shape and port timing.

Transfer ports timing:
Stock is 124.5° ATDC (111° duration) which shouldn´t be increased unless the exhaust port timing is also increased. Here is some info if you want to change its height but don´t have a digital caliper: The transfer port distance to top of cylinder is hard to read using a ruler since it's kinda in the middle of the cylinder. So I would mark the piston with the transfer distance I wanted by measuring from the bottom of the piston. Then I inserted the piston bottom end first into the cylinder from the top. Holding the piston so that the mark is equal to the top of the cylinder I could see the difference between the port height and the bottom edge of the piston skirt in order to know how much metal I needed to dremel off to raise the transfers to where I wanted them. The area to be dremeled off can be marked with a black felt tip pen.

Lowering intake port:
Stock intake distance from top of cylinder to bottom of intake port on the 48cc HT is 55.5mm (56.1° BTDC). I first lowered my intake to 57mm (60.9° BTDC) and it had good grunt (relatively speaking) and started and idled good. I then lowered my HT's intake port to 58.5mm (65.5° BTDC) and squared it off more so that it had less of a curve to it. The bike did not want to start and had no low rpm power at all. It was embarrassing having to pedal so much to get it going. It did better at the highest rpms though and gained 1mph top speed. So unless you are porting for a screamer then I don't advise going lower than 57mm. I fixed it by putting JB Weld at the bottom of the intake port to bring it back up to 56.3mm (59°BTDC) which returned the needed low-rpm torque to the engine. Look at the graph below showing the air/fuel delivery ratio change with intake timing change on a 150cc engine. A period of 118° (59° BTDC) and 125° (62.5° BTDC) gave the best results (and anything between these two).

Higher Compression
(This section has its own page now. click here)

Expansion chambers: A pipe designed for use with this engine should have a broad powerband and increase top rpm power. Unfortunately most all pipes sold for the Grubee engine are made for pocketbike racers and have a narrow racing powerband (as evidenced by the 12 degree or more baffle angle whereas motocross pipes only have a 10 degree angle). If you want it for having fun then that is fine but for street use there are no pipes available that are suitable other than making your own torque pipe. Click here to read about it. Of course you can buy a racing pipe and make it into a decent pipe by cutting the baffle in half and installing a 2" long cylinder to reduce and lengthen the baffle return wave. Most people think that the distance of the header pipe is just a matter of taste but I want you to know that you shouldn't buy an expansion chamber unless you are willing to go to the trouble to test different lengths until you find the right one to give you the best top speed.

Using a better carb will enhance power all thru the rpm range if it is jetted right. Don't buy a carb larger than 16mm unless you port for high rpm's. If you stick with the stock carb then be sure to throw away the trashy HT intake filter and put a good performance filter on it for less intake restriction and more engine protection. I tested the 12mm Dellorto against the 14mm stock NT carb and got more low end grunt and top speed using the Dellorto (because of better mixing) even though it was smaller.

Using better piston/rings is advised because the standard piston has rings that allow too much ring end gap and wear the cylinder down faster with their 2mm thick rings. Both of the following listed piston/rings are available from www.treatland.tv and the Honda piston is 1mm taller from the wrist pin so that it gives a strong compression boost without having to mill the head and discard the head gasket. The Yamaha piston has the same pin-to-top height that the standard piston has. With the Honda piston you may need to dremel the edges of the heads combustion area to allow .8mm distance between it and the piston at TDC. 

Honda Hobbit 40mm piston $30
51mm from crown to bottom of piston
26mm from wrist pin center to top edge of piston
10mm wrist pin diameter
1.5mm ring vertical thickness

Yamaha QT50 40mm piston $85
wrist pin size = 10mm, distance from top (not including crown) to center of wrist pin opening = 25mm, total length (not including crown) = 47mm, 1.5mm ring vertical thickness

A great read: Go to Micro Car Project and click onto Port_Timing_Alteration and Other_Solutions on the left hand sidebar.

from http://www.mopedarmy.com/wiki/Puch_cylinder_kit_summary
(Make booster port equal to or 7° before transfer port opening (2mm higher).
Maximum exhaust port width is 70-72% of cylinder diameter.)

Piston diagnostic photos: http://www.smellofdeath.com/lloydy/piston_diag_guide.htm

Calculate 2 stroke engine displacement:http://www.everything2stroke.com/resource/displace.php

Below are some examples of port timing from various minis:

Metrakit 65cc (43.5mm stroke) torquey. PORT MAP:http://i136.photobucket.com/albums/q194/flip27foto/PuchMaxi/naamloos.jpg
2 Transfer Ports 123° ATDC (153° duration)
Exhaust port 103.5° ATDC (114° duration)
Blowdown: 19.5°

Eurocilindro/Athena 70cc (45mm)  reed-valved fast+torquey
# Intake port (variable): Raised intake as booster-port
# Transfer Ports 118.6° (122.75° open): 4 ports + 1 wide booster
# Exhaust port 97.5° (165° open): Oval
# Blowdown: 21°

RGD/TCCD 70cc (45mm)
http://img201.imageshack.us/img201/1639/rgd70ccfi4.jpg
# Intake port 63.5° BTDC: oval
# Transfer Ports 119.5° ATDC: 4
# Boost ports 123°: 2
# Exhaust port 98° : oval
# Blowdown: 21.5°

Malossi 60cc (42mm)
# Intake port 61° BTDC (122° open): oval
# Transfer Ports 125° ATDC (110° open): 2
# Boost ports 135° (90° open): 2
# Exhaust port 100.5° (159° open): oval
# Diameter exhaust port: 25mm
# Blowdown: 24.5°

Polini 65cc (43,5mm) torquey reed-valve intake engine
# Intake port (variable): 7 including 3 boosters 123° BTDC (114° open)
# Tranfer Ports 123° (114° open): 4 ports
# Exhaust port 89° (164°): oval
# Blowdown: 25°

Airsal 70cc (45mm) "perfect timed cylinder"http://img144.imageshack.us/img144/3323/airsal70cc2vf7.jpg
# Intake port 68° BTDC (138° open): oval
# Transfer Ports 123° ATDC (114° open): 2
# Boost ports 123° (114° open): 2
# Exhaust port 86° (170° open): oval
# Blowdown: 28°

Jaaps Puch calculator 

Click the button at the variable you want to calculate and fill in all other fields.

    Spoel-/uitlaattiming = Transfer or Exhaust timing

    Timing: (total degrees port is open. Divide by 2 and subtract from 180 to get degrees ATDC)
    Poorthoogte: Port height (mm of port from top of cylinder)
    Deck: (mm from piston top to cylinder top at TDC. .8mm for my HT)
    Slag: Stroke (of piston=38mm for HT)
    Drijfstanglengte: Connecting rod length (85mm for HT)

    Inlaattiming = Intake timing

    Timing: (total degrees port is open. Divide by 2 for degrees BTDC)
    Inlaathoogte: Intake height (in mm from top of cylinder to bottom of intake port)
    Zuigerlengte: Piston length (at the intake side, 44.8 for HT)
    Deck: (mm from piston edge to cylinder top at TDC. .8mm for my HT)
    Slag: Stroke (38mm for HT)
    Drijfstanglengte: Connecting rod length (85mm for HT)
   
    Snelheid, toeren = Speed, rpm

    Snelheid: speed in km/hr (convert to mph athttp://www.sciencemadesimple.net/speed.php )
    Toeren: rpm
    Voortandwiel: front sprocket teeth (10 for HT)
    Achtertandwiel: rear sprocket teeth (44 for stock HT)
    Interne verhouding: primary gear reduction ratio (4.1 on the HT)
    Omtrek: outer circumference of driven wheel (2.133 for 26x2.125" tire)

How to Balance the Engine for Less Vibration and More Top RPM

this is from http://www.dragonfly75.com super cool information

The fix is two-fold. The first half of the fix affects vibration all through the rpm range. The second half of the fix lessens vibration only at the top rpm range where it is caused by the standard too-advanced ignition timing.

1. After you have settled on an appropriate cylinder compression (in psi. more compression gives more power) then you can change the port timing just a bit for better high rpm power and balance the engine by removing weight from the piston and wrist pin. (Drilling holes in the flywheels only offsets the weight of the piston and wrist pin.) On bikes that self-limit their mph by vibration you can easily tell if you are making it better (more in balance) by the max velocity. The first part of the fix is to lighten the combo of piston and wrist pin. I had my wrist pin drilled out from a 5.8mm diameter hole to a 7.5mm hole. With these weak engines there is no need to worry that the pin will be too weak after drilling. The same holds true for the piston. Your machinist can use a 9/32" (7.1mm) carbide drill bit to use in his lathe on the wrist pin (available for $8 from Grainger) or you can buy a wrist pin for the 48cc piston that already has a 7.5mm hole in it, available from Treatland. Next are 11gm wrist pins with a 7mm hole (1.2mm more than stock) from pocketbikeparts.com that will work in the piston for a 55cc or 60cc Grubee engine:
Generic 36mm x 10mm wrist pin & bearing $13
Generic 36mm x 10mm wrist pin $9
They probably also work in a 69cc engine since the piston is only 2mm wider. Also available is a 37.5mm long 10mm diameter titanium wrist pin (6.3mm I.D.) which is really good since titanium has around 58% the weight of stainless steel and is very strong. You can use a grinding wheel to shorten it if needed. It is 3 grams lighter than the 55cc/60cc wrist pins.
You can also lighten the piston by drilling holes in it that will be no more than 5mm from the side edges of the exhaust and intake port. Drill size is 9/32" and each hole shouldn't be closer than 10mm center-to-center from the next hole. Here's a photo showing where you can drill up to 9 holes on each side. Unfortunately, if the piston wall is 1.9mm thick (as mine is), only 18 holes will remove only 3.3 grams.
I have a reed valved engine and with the additional holes on the intake side mine totaled 27 holes and I have rev'd it to 37mph (8400 rpm) and it held up OK. Use an exacto knife to trim the outer edge of each hole to not be a sharp edge. I used a small bit with my dremel to grind a dent in the piston where each hole should be drilled. Then I used a small drill bit to make the pilot holes. (Otherwise the drill bit would wander off center.) Then I used the 7/32" bit to make the final size. Aluminum is very light so even 18 holes won't make a huge difference in weight but when it comes to engine balancing every little bit counts. Once you find the best balance you can change the porting a bit. With these two changes the vibration should be much less and the top rpm much more.
2. The second part of the fix is to buy the Jaguar CDI which is designed to spark later at rpm above 3600 to lessen the combustion/compression forces that the piston and flywheel have to push against. This approach is standard with 2 stroke engines. I think the CDI that comes with these engines is made for a 4 stroke since it does not have that essential change in timing at high rpm. That causes reduced power and reduced rpm, both of which are wanted by the company so that it can pass all countries regulations. But you don't want that because you want power and a bit more rpm without having to endure excess vibrations at the handgrips and seat.
Here's a quote from Crankshaft Design, Materials, Loads and Manufacturing, by EPI Inc.
"Combustion forces and piston acceleration are the main source of external vibration produced by an engine. They must be counteracted by the implementation of the crankshaft counterweights." [A counterweight essentially exists opposite the rod pivot by the removal of metal near the connecting rod pivot on the flywheels]

The graph here shows what I want to explain about engine balancing. The increase in centrifugal force from the imbalanced flywheels and the up/down upper piston assembly inertia (as it changes direction) is exponential with rpm. But the combustion/dynamic-compression force varies with rpm mostly due to spark ignition timing.The flywheel counterbalance (created by holes near the conrod pin) has to keep the total balance not too far from true at peak combustion/compression and at peak rpm when the combustion/compression is sharply dropping off due to spark retard.


Vibration is reported to be much more with the 69cc (80cc) engine and so this cure is even more vital for it. If not enough then you have to balance the crankshaft. Here are some reports on the motoredbike forum:
"Is the 2 cycle [69cc] motor known for a lot of vibration? I have some rubber pads between the mounts and the frame, but anything over about 15mph is just about unbearable."   post

"My seat seems to be vibrating a little too much to comfortably ride long distances at full throttle. It seems to have gotten worse recently. Any idea how I could figure out where it is coming from? The engine mounts are solid I wrapped the frame in thick leather under the mounting hardware. I'm running the Chinese 66cc 2 stroke on a mountain bike."  post

"I just finished my first motored bike build- a "Black Stallion" 66/80cc from Kings Motor Bikes. ...at the end of yesterdays ride I cranked it wide open to see what it could do. As it built RPMs, it passed a certain range and the entire bike began vibrating like the engine was totally mis-balanced! The gas tank loosened and shifted, and I had trouble keeping my hands on the handlebars! I dropped RPMs, and the vibration went completely away. I tried doing this several times, and each time I crossed that certain RPM barrier, the bike would go into wild vibration!" post

"I have a huffy panama jack bicycle, with a 80cc engine on it. I have such a bad vibration in the bike, its terrible.Ive tried rubber motor mounts, does anyone have any ideas? please help!!!!!!!!!!!!"  post

---

Crankshaft balancing (for even less vibration):

An imbalance in the crankshaft in relation to the reciprocating weight of the upper end causes vibration and a loss of power. Making sure your engine is balanced correctly is essential, especially if you are modifying the engine to work in a different rpm range than what it was designed for. Using a lighter wrist pin lightens the balance area by 4.5 grams which is enough to balance the crankshaft in a stock 48cc. If it has higher compression and is ported for higher revs then the Jaguar CDI will be needed.

There is an old fashioned way of balancing the crank, with more weight removed from the counter-balance area for higher rpm. But in studying the subject I see that the main two forces that need to be counter balanced are changed in value of force equally as rpm increases so that rpm is not a factor. That means that the counter-balance mostly depends on the upper assembly weight and dynamic cylinder pressure, not on rpm. Cylinder pressure changes non-linearly with rpm, mostly due to ignition timing. On my bike with the ignition timing curve of the Jaguar CDI it has the most cylinder pressure at around 6750 rpm.

I have two different 55cc engines using different cylinders and pistons. One is with piston port intake and the other is reed valved. The results I got testing those, along with online calculators for upper piston assembly inertia force and the centrifugal force of the counter balance is what I base my theory of balancing on. The piston port engine was way off in balance, and the other was perfectly balanced. Using it as a base point I know I have to use 61% of the conrod weight as its contribution to the upper assembly weight. And I use the downward piston force instead of the upward force (which is more due to more piston speed going upward) or the average force. The increase in piston inertia force going upwards is offset by an unknowable amount of cylinder pressure which is why I don't use it.

1st test:
Piston port intake 55cc engine (see engine details below) ported for 10,000 rpm but that achieved only 9100 since I just did the test runs with the standard exhaust pipe instead of an expansion chamber with the correct header length for 10,000 rpm. Anyway here are the details:
upper assembly weight: 122gm
additional counter balance weight removed: 9.8gm
The engine vibrated between 5600 and 7900 rpm and ran smooth before and after that rpm range.

55cc high rpm piston port intake engine:
55cc Grubee cylinder/head on 48cc bottom end
port durations: 185 exhaust, 119 transfers, 125 intake
transfer port walls removed for greater transfer area
stuffed crankcase
155 psi cranking pressure
18mm Mikuni
custom intake manifold
piston port intake
slant plug head with squish band .65mm from piston
Kawasaki KX65 piston and rings (adapted for use with piston port intake)
Jaguar CDI with Kawasaki KX high voltage coil
44 tooth rear sprocket
26" wheels with mountain bike tires
peak head temperature: 425F
2nd test:
My other 55cc engine (reed valve, Honda piston, torque pipe, 18mm Mikuni) with 77.3gm upper assembly with 15.8 grams removed via a 9.15mm diameter hole thru both flywheels allowed my engine to go up to 9150 rpm (downhill) without any bothersome vibration.
Here are the force evaluations of the two engines at 4000 rpm:
Upper assembly weight (piston, wrist pin, bearing, 61% of conrod):
piston port engine: 134.5 grams
reed valved engine: 120.5 grams
Downward assembly inertia force at 4000 rpm:
piston port engine: 78.45
reed valve engine: 68.7Centrifugal force of counterbalance*:
piston port engine: 60.2
reed valve engine: 68.7  
Centrifugal force divided by Downward force:
piston port engine: .767
reed valve engine: 1.00 
*In figuring the counter balance weight you have to include everything that would affect it. As example: my flywheel came with two 11.5mm diameter holes through both flywheels. The stainless steel there removed adds up to 50 grams. The conrod pin added 3.3 grams after the weight of the conrod pin holes weight were subtracted from it. The part of the conrod that is around the bearing, and the bearing itself, weigh around 30 grams. The centrifugal force has to be figured at the two distances of 19mm of the conrod, and 36mm of the counter balance holes.

Now we can calculate the needed "missing" balance weight for the 48cc Grubee engine. What I first noticed is that the existing balance holes are not the same distance from the center of the crankshaft as the connecting rod pin is. That is important because the farther a weight is from the centerpoint the more centrifugal force it has for the same rpm. Using a test weight of 1kg at this site I see that at the 36mm distance of the balance holes gives 1.9 times the centrifugal force as 1kg at the 19mm distance of the conrod pin. 
Upper Assembly weight and downward inertia: 61% of the conrod is 43.5 grams and the piston assembly weighs 79 grams for a total of 122.5 grams. That weight at 4000 rpm (with 1.5" stroke and 3.35" conrod length) gives 71.45 pounds inertia force.
Counter balance weight and centrifugal force: The two factory-placed holes of 11.5mm diameter equate to 50 grams of missing weight which gives 71 pound-feet of centrifugal force at 4000 rpm (at 36mm radius). 30 grams of conrod bearing and "end" added to the 3.3 grams of the extra conrod pin weight gives 33.3 grams which gives 25 pound-feet of centrifugal force at 4000 rpm (at 19mm radius). 71 minus 25 equals 46 pound-feet.
Centrifugal Force to Downward Inertia Force Ratio: 46/71.45= .64 which is terrible. 
Calculating needed counter balance weight removal: 71.45 - 46 = 25.45 pounds of force which requires 43.7 grams weight removal at the same 36mm distance as the existing holes. A 10mm diameter hole drilled through both flywheels will result in 41.5 grams removal according to this site (be sure tomultiply the resultant weight of kg by 1000 to get grams). But usually holes drilled are not perfect and so you can add about .15mm to the size. And so a 10.15mm hole will remove 42.8 grams which is close enough. A good quality drill bit of an equivalent 25/64" size is available for $16 online from Grainger. You can drill the hole yourself with an electric drill but it is hard and slow going. Best to do it at the machine shop.
piston inertia calculator

centrifugal force calculator 

steel weight calculator

Since upper assembly inertia and flywheel centrifugal force stay neck and neck thru the whole rpm range then it is just the changing compression/combustion force that varies with rpm. That is influenced by cranking compression and ignition timing. My balanced engine has 165 lbs cranking compression. High compression and advanced ignition are typical of enduro bikes, not racers. Race bikes have lower compression (typically 9:1) and retarded ignition. So my engine, being like an enduro bike, is just right with a 1/1force ratio. A race  bike may need only .95/1 as a force ratio.

Here is a picture of my crank assembly with an additional balancing hole just above the conrod pin. The 6 blue holes are lightening holes for better acceleration (although I wouldn't recommend any more than 4 if the bike is for street use). The blue is foam filling half the hole. The ends of each hole were later filled with JBWeld. I used foam just to reduce the amount of expensive JBWeld used. The conrod hole and two factory balance holes are already filled with JBWeld for increased crankcase compression.

For the "80cc" engine, with a piston assembly of 107.6 grams and 11.15mm  counterbalance holes at 36mm from shaft center I figure a 12.6mm extra hole is needed to balance the engine. (drill bit)

Concerning determining the weight of the lower conrod bearing and the part of the conrod that is around the bearing: I figured that by dipping the two into a measured amount of water and seeing how many cc (ml) they raise the water level. My 48cc had an equivalent 30 grams.

zanella due Manual includes hardwire

despiece del motor(similar)

about to get to 5000 visits!

thank you very much to all who helped us with their views wherever they are the blog grows more and more and it helps us to be teaching and learning more and more about these beautiful 2-stroke engines that resist both.
greetings to all!!
PS: sorry if the blog is inaccessible or have trouble entering the problems we are looking for, even we do not know because sometimes the blog is inaccessible

for those who have ignition problems

here is a video on how to check the spark plug, crucial for proper engine operation

clean carburetor

for those who do not know how to clean and disassemble your carburetor I leave this video, luck!

we renew

Hello I am writing to thank you for visiting the blog daily and the questions I sent by mail, we have more and more daily visits, thanks to which we are now writing more often. do not hesitate to ask any questions you have and thanks to those who help us with their clicks!!
thank you blog grows more and more.

regulate carburetor

those who wrote before, to have brown color spark plug must be regulated either the carburetor in this video shows how to adjust the needle that regulates the passage of gasoline

motorized bicycle ride

basic maintenance

hello I'm writing this blog back in slowly growing. Today I bring you some small tips when to use and save your motorized bicycle:
* Always when the motorized bicycle is off key gasoline close
* Let her warm booting when and if needed to put the primer, so that it more naphtha and lubricate fence but since the piston and the cylinder todabia not dilated and not enter regimen.
* If you can always use synthetic or semi-synthetic oil, mineral never with the mixture 1/20
* Clean your carburetor and exhaust every one or two months, it is convenient to use a filter on the carburetor
* The plug must be always with the internal ceramic brown, if not it indicates that the adjustment of the carburetor then'll upload a video with this tutorial
* The best plug I tried so far is the ngk BP6HS works great.


watch as these Motorized bicycles factory!!

more

electric bicycle

I leave a video so they know how to clean your carburetor

this video is aimed at teaching them how to disassemble, clean, and assemble your fuel system including issue of his motorized bicycle carburetor, but it can also serve a moped owners. good video here

answer questions

any questions you have about your motorized bicycle or moped podre I know the answer without problems and if it is I'll find out and the will comment, discuss their questions

2 stroke engine boost

this is translated with google translator, the original language is Spanish, it was very long to translate normally

BASIC SKILLS FOR PREPARING A CYLINDER :

ADMISSION :
Admission takes place , usually through an opening in the cylinder which is connected to the carburetor , and is called the third opening admission ; understood as 1st and 2nd opening the expulsion and transfer.
On admission to the third opening , which is the piston valve for controlling the input and the mixture into the crankcase , thus the admission duration is proportional to the height of the opening and its position in the cylinder.
With this control system , you can only perform a range of admission ; symmetrical and this is a limitation that does not allow for the best possible distribution diagram for asymmetric engine diagram , but permits the best symmetric diagram almost never matches above (with a symmetric diagram can not for example, increasing intake just a teaser , because each advance opening followed by a closing unwanted delay . This problem can only be resolved in rotary valve engines is generally the shaft or engine crankshaft , for example the typical simple scooter ) .
Another system is that the reed valve is simply one or more layers which open due to the depression created by the piston in the upward phase and closed by the effect of its elasticity when said depression stop ( idle ) and remains banging shut against its seat when the piston descending phase increases the pressure in the crankcase .
The type of material of the sheets is what promotes its elasticity and closing down its phase


CYLINDER :
To prepare an engine , you have to know what the engine can know through a very simple formula :

but there is another formula in which both the diameter and the stroke is expressed in inches

V = 0.785 . D ² . R . N where:
0.785 = a fixed number unchanged.
D = diameter of the piston in Centimeters
R = stroke in inches
N = number of cylinders
Then follow the previous example and as a centimeter is 10 mm divide by 10
D = 48 mm = 4.8 cm
C = 56 mm = 5.6 cm

THEN : V ² = 0.785 X 4.8 X 5.6 = 101.2838 C.C
IF YOU WANT TO HAVE ONE LITER LITER AS 1000 cc divide it by 1000 , I mean = 0.1012 83 liters .

One of the biggest problems is the spread of heat inside the cylinder and that 2 stroke engines have additional problems because they are warmer than other areas because as we saw above the fresh mixture cooling flows inside these areas , and is adds to the problem that the cylinder has holes inside (Willey ) with the elevated temperature can undergo twisting. To avoid this, the cylinder is provided with cooling fins for air to flow through them to cool the cylinder ( these fins should be clean , to favor the action of air ) for high engine speeds disperse more heat fins very thin and very close to each other and better low speeds and more thick fins spaced . The cooled water-cooled cylinders much better and you should pay attention to the pumping system to circulate water and cool in the radiator.
The problem that the heat produced in the metals is that dilates and some expand more than others depending on their composition. The expansion produces a lengthening and widening ( 2T engines normally run at 200 º centigrade THIS TEMPERATURE STANDARD BUT NOT ENOUGH ORIENTATIVA ) .
The expansion of a metal we know according to the following formula:

Dilation = Cet . D . T
Cet = Thermal expansion coefficient FOR EACH GRADE LINEAR metal in question
D = diameter of the sleeve in mm
T = temperature in degrees Celsius .

Example : The thermal expansion coefficient for each grade cast iron is 0.000010 .
D = 48 mm
T = 200 ° C then : Expansion = 0.000010 X 48 X 200 = 0.096 almost one hundredth of a millimeter
If the cylinder was plated aluminum would be greater dilation , dilation of chromed aluminum is about twice .

CYLINDER WEAR
Influence on wear : heat, rubbing materials and the piston speed

PISTON SPEED :
The piston speed is easily calculated using the following formula:

Vp = C . N / 30000 wherein:

Vp = velocity of the piston in m / s
C = Stroke in mm
N = number of turns of the engine R.P.M
30000 = fixed unit dependent on the units used

EXAMPLE: 58 race motor that spins at 9000 RPM then:
Vp = 58 x 9000/30000 = 522000/30000 = 17.4 m / s ( FORMULA IS GOING TO BE USEFUL FOR CARBURETION ) .

SHIRTS BY TYPES OF FRICTION MATERIAL
The cylinders , we saw that they were surrounded by a material that promotes cooling , this material is usually aluminum, for its light weight and ease of cooling.
Do construction can be three types:

Iron Shirt 1 ( cast ) aluminum body
The two parts are made separately , are prepared and placed inside the sleeve body for the body it is placed in an oil bath , higher than 200 ° approx. To dilate and embedding of the cylinder is simpler but requires the use of a press.

Casting 2nd centrifuged
It melts the aluminum body directly over the shirt .

3rd chromed aluminum cylinder
Currently is the most used is made and shirt body in a single casting and is applied through an electrolytic bath , a bath or hard chrome layer so called to distinguish it from the typical decorative chrome is bright this bathroom is like tenth least 1 thick. These cylinders are not easy to rectify , as it would give them a new electrolytic bath and that maybe we are not profitable.
THE REASON GIVEN CHROME BATH IS BECAUSE NO TWO SAME MATERIALS AS may rub ATOMIC AFFINITY FOR HIGH TEMPERATURE TEND TO "hook " ALMOST COMING TO A FOUNDRY . THEREFORE NEVER BE A PISTON SLIDE ALUMINUM ALUMINUM ON A SHIRT AS WELL AS IN A CYLINDER CHROME DO NOT USE SEGMENTS ( AROS ) CHROME AND A SHIRT ALSO CAST IRON CAST IRON RING . HERE IS WHERE IT JOINS THE STRENGTH OF THE VARIOUS MATERIALS , IF YOU HAVE CYLINDER CHROME CAST IRON AND SEGMENTS . CHROME CYLINDER IS MORE HARD SEGMENTS , THEREFORE, be spent SEGMENTS WILL BE MUCH FASTER AND MORE OFTEN THAN TO CHANGE BUT THE CYLINDER MORE HARD ON THE CONTRARY IS THE SHIRT IS CAST IRON AND CHROME RINGS , THE NEW RINGS AND CYLINDER WOULD be spent BEFORE AND WOULD be rectified , SO THE CHROME CYLINDER DURAN , IF YOU CARE , MORE THAN CONVENTIONAL CYLINDERS . ALTHOUGH HAVE CONVENTIONAL OTHER BENEFITS AS ARE THE GROUND AND IN MOST CASES, THE POWER disarm, THIS LAST DETAIL TO CONSIDER WHEN THE POWER TO MODIFY OR EVEN BUILD A SHIRT WITH A DIFFERENT DISTRIBUTION .

As transfers polish . -
We must be clear what is and what is polishing file : Polishing is to remove rough edges and file it down or removing material .
When we want to advance or delay the entry and exit of gases, ie vary the distribution of an engine , you can , as an option, enlarge the cylinder ports , both the intake and the exhaust . Transfers of transfer, are the little ones that connect the crankcase to the cylinder and whose function is to effect scavenging normally rarely enlarged, and only changed the angle so that the sweep is more or less rapid and direct, as explained in 2T engine operation .
Normally the cylinders are usually of two pieces, a shirt where the piston touches another block that is outside the cylinder lining is usually made ​​of aluminum and can carry fins, if air cooling or cavity through which the cOOLANT ( dirty water and corrodes aluminum , you can make mixtures of distilled water mixed with glycerin neutral , but not worth it , comes perhaps more expensive than the products sold ) .
The polishing is to remove all impurities or roughness remaining in the cylinder block casting to prevent soot buildup and promote fluid gases. There preparers who says it is not advisable to polish the transfer of transfer, because those ridges create a turbulence that favor the sweep , I think that's tastes and theories, I personally like polished .
To polish , you need to have a micro - motor or a mini - drill , which was installed some strawberries whose tip can be made of stone or diamond ( diamond is advised although the stone is much cheaper ) these stones the there are several coarse grain is to abrade or a refiner , as different shapes and sizes. Once reviewed and refined , is passed fine sandpaper to remove all stripes who have left the strawberries and since we are on task, if you do you can top with strawberries termination rubber , which also exist to wear and for brightening . The final result depends on the time you employ and careful you are. " If you strive much you can even comb because you reflect on the polishing so called " mirror polished " .



In these images , it can be seen as the entire duct and contouring as in the transfer of transfer, the center wall is tapered to avoid interference of the gases and the mixture
If only done polishing the ports , they should not touch the edges of the shirt through which the piston to prevent being rounded edges and snagging the segments or " rings " , it is also advisable to place a piece of cardboard attached to cylinder to prevent possible scratches in case of escape bore
As we mentioned earlier, one of the qualities of cast iron cylinder sleeve , is the possibility to disarm by operational readiness , building a new one if you already rectified to limit construction or other distribution.

The general idea with all the " preparers Beginners" is that enlarging the holes , you get more power and engine performance, this theory is partly true, and I say in part because sometimes hurts and engine performance worsens .

We must be very clear concepts of engine operation, and we know that engine performance so we can determine its size or position.
In different articles , we'll more or less , giving an explanation on the functioning of the different organs of the engine and some do an introduction to the preparation of that particular piece , but try to make a collection of modified parts in a specific section .
In the right figure we see two shirts of the same engine , the shirt of the Left , is the original shirt on the right and a shirt made and modified for better engine performance. It can be seen that what is wanted to achieve was a good sweep and trapped gas and so we chose to make a smaller transfer for the pressure and velocity of the mixture was superior and conduct a sweep and advance best to cut closing the sweep and to hold more gas quantity . These operations require a series of calculations for the operation is optimal , otherwise we run the risk of catching a lot of gas and burned and expelled , causing detonation and ignition problems .
The height can be seen or available in the cylinder are slightly different, as compared to higher PMI , that is, maintaining the opening but shortens or forward closure. ( Remember that the opening of the exhaust port as the transfers are performed when the piston is down , you can also observe the recess of settlement of the shirt is highest precisely to favor the expansion . )


HEAD . -

COMPRESSION RATIO INCREASE


The compression ratio indicates the order of magnitude that the air-fuel mixture will change in volume within the cylinder, when compressed. When the engine is running at a certain number of rpm , each time the piston descends from TDC ( Top Dead Center ) to BDC ( bottom dead center ) enters the cylinder , theoretically , both mixing volume as has the engine displacement .
At this point , the piston will start to rise from BDC to TDC , but during the climb, at 2 T engine , you find that the Exhaust Port is open for a while, while the piston not closed. During this time the mixture will escape without burning or compressed so that compression will not begin until the mixture of the exhaust port is fully closed . ( later will comment on this point)


Increasing the compression ratio achieved a power increase but be careful not to go to that there is no call laexplosión uncontrolled detonation ( see gasoline ) . for it is advisable not to move from a higher compression ratio to 12:1 in small engines.

The less cylinder engine has more supports compression ratio . This is because the effect of detonation appears more easily in larger displacement engines . There are some universal values ​​that should be reached by the maximum power that will provide hassle . These values ​​are suitable using unleaded 98 octane and you can see in the table. If the octane of gasoline is higher , you can even get to 17:1 as the famous " Dragsters "



The more compression ratio with a motor , the mixture will be more pressure when the piston is at TDC and release the piston with more force and speed.
This high pressure will cause a very rapid rise in temperature, and thus the gas molecules to flutter quickly. This upheaval cause rapid swelling of the combustion mixture producing high quality and high speed.
This is basically the reason that increasing the compression ratio we will get a higher peak power (also get more power to any number of rpm , not only in the maximum power rpm ) .
In the right chart , we can see . , Performance varies depending on the combustion compression ratio . With increasing compression ratio is improved in combustion efficiency , within certain limits .

So for example when passing from a compression ratio of 7:1 to 10:1, increasing 3 points, it shows great improvement in the power provided by the engine , yet passing from 10:1 to 13:1 , also increased 3 points, do not notice much improvement .





In these images the procedure to follow: image 1 is the piston TDC and in image 2 is filled with liquid to know the exact volume . It is clear that the way to increase the compression ratio is to reduce the volume of the chamber of the cylinder head , for this we use two methods are the lower base of the cylinder head thereby reduces the volume and the second method is fill the stock with the same material that is built the butt , usually aluminum, and then give the desired shape and volume , this method is more complicated but can be given to the dome of the head as desired to achieve a most effective sweeping .

In the images 3 shows a stock with normal dome in Image 4 a head with dome shifted also called high turbulence

How to calculate the cylinder volume when closing the exhaust.

As we mentioned above, until the Exhaust Port is not closed completely, the actual compression will not start .
The mixture volume was in the cylinder at closing of the exhaust port anger increasingly being lower due to the rise of the piston. When the piston is at TDC , the mixture will come to occupy the minimum volume : the volume of the combustion chamber in the cylinder head carved .
Measuring the compression height is easy. just need a vernier caliper , measure the height of the exhaust port , from the head of the piston when in the PMI to the top that is when closed and subtract that measurement to engine stroke .
Knowing the diameter of the motor and the compression height can calculate the compression volume using the formula used to calculate the engine with the modification that instead of using the full stroke is used as the race from the exhaust port is closed:


Rc = 64.77 + 6.82 / 6.82 / / Rc = 10.49

This means that if before we had a volume of 7.2 cylinder head and now a volume of 6.82 , we have reduced the volume of 0.38 cc .
Using the same formula that we have been using for calculating volumes but we can calculate the extent inverting planning in the butt to get the compression ratio :
HEIGHT = ( 4000 x VOLUME ) / ( 3.1416 x DIAMETER ² ) where:

VOLUME : The volume to reduce according to Example 0.38 cc
DIAMETER : The diameter of the cylinder 52 mm
HEIGHT : The distance in mm to remove the cylinder head.

Height = 4000 x 0.38 / 3.1416 x 52 ² / / A = 1520 / 84.95 / / A = 0.17 mm
This means you have to lower the top of the cylinder 0.17 mm . and obtain the 6.82 cc in volume if the cylinder head permits.

Issues to consider when increasing the compression ratio . -
As we were saying until now, the compression ratio depends on the volume trapped in the cylinder when the exhaust port is closed , so it is calculated from the time, but that's true in theory and influencing factors to enhance the trapped volume .

Can we really start to compress the fuel before the Exhaust Port is closed ?


That's fine of course not, but nevertheless when the motor rotates at high revs , the piston is moving so quickly that sends fuel so fast and less time to escape this open , because at that speed , the static volume cylinder caught is greater .


This fools that improves efficiency at higher rpm . Thus, under actual operating conditions , understanding our true relationship dynamically improves withincreasing rpm !
Rarely approaching 100 % efficiency of the engine, but with modifications to the exhaust port and a system with a " suction " adequate and well-designed shock , (either collecting or taking advantage of the sweep gas to effect complete evacuation by exhaust ) and the negative pressure created in the crankcase to push fuel through the transfer transfers ........ then we can reduce the losses of the " fill " (or pressure) before the exhaust port is closed at a certain rpm range of operation, in that case , we can even exceed 100% entrapment efficiency gas ! .
This means that for example a 125 cc engine , actually can trap more than 125 cc. fuel than the volume of the cylinder and then " compress " in much smaller volume above the piston prior to the spark .
The problem here is that this requires a suction and pressure system , synchronized with the exhaust and that occurs only in a specified range of power , when the engine accelerates outside that band power pulses in the suction and the systems download are out of phase and actually contribute to a loss in efficiency trapped .
Now knowing what actually happens when the engine is in the desired powerband , perhaps we can begin to see what is REALLY points to consider when getting a good compression ratio :

1 º . - How big is the engine. This means the volume in the cylinder with the piston at BDC ( in English is called BDC )

2nd . - What is the volume when the piston is at TDC ( TDC ) is the volume in which compressed gases trapped or what is the same, the volume of the compression chamber .

3rd . - What type of gas trapped dynamic efficiency is achieved according to the engine design . Here the range can be as low as 75% or even slightly higher than 110% on a tuned optimally .

4th . - How big are the transfers and exhaust port. Transfer the transfers of large , they tend to be less effective in filling because gases circulate with less speed and low pressure by sweeping causing trapping waste gas from the last combustion discharge expelled. Due to this as well, tend to make control of the process of combustion without detonation and / or - the ignition problems . Mainly for these reasons , you can get high compression ratios in engines with large Lumbreras without risking problems.

5th . - What is the fuel octane level will use the engine. The high octane and special fuels such as methanol have increased resistance to spontaneous combustion support " Detonation " " and can withstand higher compression ratios and can wait for the spark plug to fire them instead of" triggering " . If we use a mixture strict high octane fuel , we can raise a higher compression ratio . ( Typical compression ratios of typically 10:1 to 11.5:1 or even in some cases slightly higher . With fuel 100 octane, in the cylinders with a diameter of 70 mm can often tolerate a 13.5:1 . dragsters using a 110 octane fuel to the combustion chambers can tolerate well designed or 16:1 and 15.5 times higher. methanol in automobiles and those engines which use a mixture of methanol and nitromethane can reach 17:1)

A key issue to consider when lowering the head, is the distance between the piston and cylinder wall before you start the stock dome squish called for the piston head not trip creating a significant shredding motor. To avoid this, we must first reduce the stock, making the measure that has originally and angle.


SQUISH

A somewhat personal translation word might be " splash separation and angle ."

The word squish , is now becoming , a term quite used although some may not know exactly what is its importance in today's engines , both 2 and 4 stroke .

The squish , refers to the distance between the piston dome and the band or track that exists before the compression chamber itself. This band may be flat or have a certain angle and along with the piston , make a pushing function of trapped air toward the compression chamber . This pushing the compression chamber , allowing the compression process is faster favoring less compression work , higher compressive pressures , more work expansion , ignition coordination ... This means more power.
You should know that although the squish is beneficial, not always better , if there's much squish angle , it causes more turbulence that we can produce a severe shock causing detonation in the engine or a hole in the piston head .
To avoid these problems , we need to have a gas velocity " Meansquish ( MSV ) " with values ​​between 0-25 m / s getting good results with values ​​between 15 to 20 m / s . ( For an engine of 250 cc , the clearance between the piston and the splash band should not be less than 1mm in smaller displacement engines can be used smaller separations .
Separating the splash band is important for the gas velocity and often fall into the trap of not maintaining this separation when we lower the head to increase the compression ratio .

For this measurement , proceed as follows:
1 º . - Disarm the ignition and head
2nd . - Placed on the head of the piston 4 bits of lead solder or tin in a position opposite each other , ie 0 °, 90 ° . 180 ° and 270 ° , that sujetaremos a piston head with a little fat


3 º . - Mount the cylinder head with a new gasket and pressed with the contact pressure we're going to give ( this point is important , because if we give less pressure , we can vary the measure because later, when we give more pressure board yields and the stock is closer to the piston head ) .
4th . - We put the nut on and with a large tool to pry , turn the engine until the pieces of tin placed on the head of the piston touch the butt and we carefully with force until the piston exceeds the PMS and descend . (this must be done carefully because if we put a tin very thick, you may not have enough force to crush )
5th . - Disarm the stock and note in the position they were tins and measure . ( Usually usually have the same distance around the perimeter of the piston head , but in some cases vary the measures, so it is important to write it down )
6th . - Is measured with a micrometer tins and we observe that on one side are more flattened ( the overlap portion attached to the sleeve) and a minus side . By measuring the entire surface can know what is the exact angle with respect to the dome of the piston head ) .
7th . - This measure should be to spare the time to lower the head and only reduce the height and angle when you have made the appropriate calculations for good gas velocity ( MSV ) .

CRANKSHAFT


The crankshaft is very important in the 2 stroke because of its shape and design , we will get the necessary pressure in the crankcase for optimum performance of our engine . As already mentioned above in the " CHECK ENGINE 2 T " , space or volume not occupied by the motor organs is called " SPACE HARMFUL " so that space is intended to be minimal and to this end, gives the drive shaft of a steering wheel that make counterweights and filling to reduce that space , and the crankcase is designed to almost touch the crankshaft and that volume is minimal.
One of the changes that have the effect usually in an engine, is the lightening of its parts , as we illustrate later in the " IMPROVEMENTS " .
In the figure we see two crankshafts , one lightweight and one normal , if we decide to lighten a crank , it is clear that we have to fill the space that we have somehow lowered , so that the space Harmful, not excessive and not lose the effect crankcase pressure .

This filling can be made by filling the crankcase or crankshaft giving the caps some species . ( Will be illustrated later in the section improvements.

When we speak of a reinforced crankshaft , it does not mean fatter or thicker, but rather stronger or more resistant .
In all types of preparations , which is made to lighten parts , not only the engine but also the frame, but if lighten over , can achieve a delicate workpieces . High competition vehicles ( World Rally Championship , Formula 1 , motorcycle world ... ) use last generation materials (carbon fiber , titanium ..) materials that are expensive and used only an elite , achieving high strength and very little weight.

Cranks . -
The connecting rods are made up of three parts : foot rod ( which is the top, which houses the piston pin ) the big end (which is the lower part , which houses the crankshaft bolt ) and the rod body (linking these two parts ) . body length of rod that connects these two parts , no influence on the race, as the race gives the crank housing to the rod , which is more or less out of the center of the circumference of the crankshaft. What it does, is that the rotation is faster or slower , depending on their length.
rod that transmits only circular motion of the crankshaft and converts it into a linear (straight ) piston .
The length of the connecting rod, engine influences that is more or less rapid , but not only because I have to make travel more , but have less travel because the ports are more close to each other getting a distribution with faster sweeps .


In this illustration it can be seen the preparation of a rod from the aligeramento

oth the big end and the connecting rod are made of a metal " friction " or " BABBITT " which is usually a tin -lead alloy , and antimony with small amounts of copper and nickel metals are quite soft and need to are well prepared and LUBRICATED . Also used leaded bronze alloy ( leaded copper ) and other zinc , copper and aluminum with better mechanical strength than the conventional babbitt .
So if the babbitt is stronger than the original part , we can say that this piece is reinforced.
Keep in mind that the engines are able to withstand a given load revolutions and ultimately a brush and heat set , but the pieces do not come to the limit of their endurance , they have to ensure reliability and that margin is usually quite large , so that is where we have to build on that margin , preparing the pieces to get the most performance and of course create sufficient lubrication for the speed increase does not generate excessive heat

CARBURACION


DIFFUSER DIAMETER . -

The diameter of the diffuser is very important for the engine operation , some thought that increasing the diameter of diffuser , the engine ran faster because aspired more air and gasoline. The reasoning is logical but not entirely true , because you have to consider several factors.

The main thing is useful to know that the force of the piston corresponding to the maximum torque ' , is achieved in the diffuser there is a flow rate of at least 90 mtros / second , or what is the same, a rate of 324 Km / hour which allows vaporization and optimum combustion .

To obtain this rate , it is necessary that the diameter of the diffuser is not excessive because:

1 the amount of air flow when the piston descends aims have to be the same as that passing through the diffuser to achieve a continuous flow .

2nd the two volumes of the cylinder and the diffuser must be equal .

For that we must keep in mind that :

The volume 1 is always the product of the flow rate through the area (section)
2 The speed of passage in the diffuser is obtained by multiplying the speed of the piston by the ratio of the barrel sections and the diffuser or the squares of their respective diameters.

ie applying the formula:

Vd = Vp . D ² . / D ²

where:
Vd = speed diffuser.
Vp = piston speed .
D = diameter of the cylinder.
d = Diameter of the diffuser.
Suppose an engine with :

Diameter , D = 47 mm
Carrera C = 39.2 mm = 0.039 meters.
D = 21 mm diffuser
R.P.M , N = 11000

Calculate the speed of the cylinder ( remember that the race is placed in meters)

Vc = C. N / 30 / / 0.039 x 11000/30 = 14.3 m / s

Calculate the speed of the diffuser :

Vd = Vc . D ² / d ² / / 14.3 x 47 ² / 21 ² / / 14.3 x 2209/441 / / Vd = 31588.7 / 441 = 71.6 297052m / s

As the area of the circle is A = 3.1416 x R ²
then:
Cylinder Area = 3.14 x 23.5 ² = 1734.94454
Diffuser Area = 3.14 x 10.5 ² = 346.36059 .

As we said that the volume is the product of the velocity by the area then we have:

Cylinder volume = 14.3 x = 24809.7069 1734.94454
Volume diffuser 297052 = 71.6 x 346.36059 = 24809.7069

Then the volume of the cylinder is equal to the diffuser so we are meeting the basic requirement , the diameter is correct.

We will find the number of RPM corresponding to a speed of 90 m / s with the following formula :

N = 30.V. d ² / C.D ²

Wherein:
30 = fixed number (as measures used )
V = air optimum speed 90 m / s
D = diameter of the cylinder in mm
. diffuser d = diameter in mm
C = Piston stroke in meters.

N = 30 x 90 x 21 ² / 0.039 x 47 ² / / 2700 x 441 / 0,039 x 2209 / / N = 1.1907 million / 86.15 / / N = 13 821 RPM
It wants to tell us that when the motor runs at 13821 rpm in the carburetor are optimal flow 90 m / s

With this number of rpm we will check if the engine is running at these speeds , the speed of the diffuser corresponds to 90 m / s optimal .
cylinder speed
Vc = 0.039 x 13821/30 / / Vd = 539.019 / 30 / / Vd = 17.9673 m / s

speed diffuser
Vd = 17.96 x 2209/441 / / Vd = 39673.6 / 441 / / Vd = 89.9994 .....
Now let's do the same operation but sharing what the bore and stroke

Piston diameter D = 39.2
Piston stroke C = 47 mm = 0.047 meters
Diffuser diameter d = 21 mm
R.P.M N = 11000
then
Cylinder speed Vc = 0.047 x 11000/30 / / Vc = 17.2333 m / s
Diffuser speed Vd = 17.2333 x 1536.6 4/441 / / Vd = 60.0484 m / s

Ac = area of cylinder 16 x 3.14 384.16 / / A = 1206.8742
Diffuser area Ad = 3.1416 x 110.25 / / Ad = 346.3605

Flow rate:
Cylinder : Vc = 17.2333 x 1206.8742 / / Vc = 20798.4251
Diffuser : Vd = 60.04 84 x 346.3605 / / Vd = 20798.3938

R.P.M to find the flow of 90 m / s

N = 30 . V . d ² / c . D ² / / 2700 x 441 / 72,222 / / N = 16486.66 rpm

Roll speed check cylinder speed finding ::
Cylinder speed :
Vc = 0.047 x 16486.66 / 30 / / Vc = 25.8291 m / s
Diffuser speed :
Vd = 25.8291 x 1536.6 4/441 / / Vd = 90 m / s

CONCLUSION :

We note that the diameter of the diffuser is not a function of the displacement , but according to the VOLUMES , this is clear , as the engine displacement shown here are different since the Motor A, has a displacement of 68 cc and the B engine has a displacement of 56.72 cc .
If we apply the formula of the cylinder ( see Cylinder )

Displacement Motor A = 3.1416 . D ² . c / 4000 / / 3.14 x 47 ² x 39.2 / 4000 / / C = 68 cc
Displacement Motor B = 3.1416 . D ² . c / 4000 / / 39.2 ² x 3.14 x 47/4000 / / C = 56.72 cc

We deduce :

Piston speed
A = 14.3 m / s
B = 17.23 m / s
Revolutions per minute:
A = 13821 r.p.m.
B = 16491 r.p.m.
We clearly see influences cylinder construction ( bore and stroke ) engine performance
The smaller engine displacement is the same diameter diffuser and spins much faster at the same pass gasoline has more friction between piston and cylinder that rotates at a higher number of revolutions thus more wear and more heat produced by friction , by thus more expansion

Because the size of the carburetor will influence both the maximum power ?
To answer this we must consider two factors:

1. Fuel atomization . The faster the air flow through the carburetor , the better will be the gas atomization . On carburetors small diameter air speed is high and therefore the better the atomization of the fuel in the air

Two . Resistance to the passage . The faster the air flow through the carburetor , the greater will be the air friction with the walls . On carburetors small diameter air speed is high and therefore the air will have great difficulties circular .



As we see here two phenomena occur that are opposites. We improve atomization of gasoline with a carburetor very small, but at the same time we will be offering great resistance to the passage . We then reach a compromise. It has long been made ​​rigorous studies on this and came to the conclusion that for maximum performance , the air must flow through the carburetor at an average speed of 90 m / s . There is a graph that captures the relationship between the velocity of air through the carburetor and relative peak power will give us the engine
In the graph it is clear that the maximum power point corresponds to the above 90 m / s . If we use a larger diameter carburetor will air flowing at slower speeds and maximum power will be lower, but only slightly . Imagine a 125cc engine when air flows at 90 m / s through the carburetor , the engine provides optimum performance of 34 hp .

If the circulating air at 70 m / s , larger diameter carburetor , the maximum power of 30 hp serious offer about .
If we use a smaller diameter carburetor , air will circulate faster and maximum power will be lower , decreasing in a rather abrupt . In the above example if we did circulate the air at 140 m / s the maximum power that would offer to be about only 17 hp .
As shown in the graph and in the example , bad is a carburetor too big as one too small, but it is always better to spend a little bigger than a child. , Although it is clear that it is always best to use a carburetor to circulate the air at exactly 90 m / s , as this will achieve optimal engine performance .