Why do bike motors make so much more power?

[cuttinties]

Well which engine would rev more short stroke.

Short strokes yes but the piston relative to the stroke doesn't travel very far. So it's not moving as fast. The name of the game in scavenging is to separate everything very quickly.

 

[jar944]

Flywheel effect

I'm confused on the" longer stroke makes faster piston speed" I thought the opposite?

You are thinking about rod length and piston acceleration

 

[Guido Salvage]

[QUOTE="lone wolf, post: 5182236, I'm confused on the" longer stroke makes faster piston speed" I thought the opposite?[/QUOTE]

How is this for a thought from the sidelines... Remember, I am not a mechanic, but I changed a spark plug once.

Both engines are turning 12K, one with a 2" stroke and one with a 4" stroke. The piston on the one with a 4" stroke has to travel farther in the same time as the the piston with the 2" stroke.

 

[lone wolf]

Short strokes yes but the piston relative to the stroke doesn't travel very far. So it's not moving as fast. The name of the game in scavenging is to separate everything very quickly.

But the crank would be moving faster on the short stroke giving more RPM and the long stroke would have a bit more torque and be a bit slower right?

 

[lone wolf]

[QUOTE="lone wolf, post: 5182236, I'm confused on the" longer stroke makes faster piston speed" I thought the opposite?

How is this for a thought from the sidelines... Remember, I am not a mechanic, but I changed a spark plug once.

Both engines are turning 12K, one with a 2" stroke and one with a 4" stroke. The piston on the one with a 4" stroke has to travel farther in the same time as the the piston with the 2" stroke.[/QUOTE]
Right but typically a longer stroke turns slower then a short stroke right?

 

[jar944]

You can pipe a saw as well as a bike. Tuned pipes won't gain you all of this mythical power. 15-20% gains is being pretty generous. Piston ported or not pipes aren't the deciding factor of power difference between short stroke and long stroke.

********

lets use the 6400 as an example
48mm bore X 37mm stroke

compare it to the KTM 65sx listed
45mm bore X 40.8mm stroke

look @ the KTM HP (just under 18 modified and just under 13 stock)

 

[cuttinties]

But the crank would be moving faster on the short stroke giving more RPM and the long stroke would have a bit more torque and be a bit slower right?

It depends on the application. But in most cases yes.

 

[cuttinties]

********

lets use the 6400 as an example
48mm bore X 37mm stroke

compare it to the KTM 65sx listed
45mm bore X 40.8mm stroke

look @ the KTM HP (just under 18 modified and just under 13 stock)

3mm of stroke and closed ports and a pipe. And you got 27% "I have a potty mouth"

 

[cuttinties]

Remember that although it looks like the pipe alone gained you 27% there's many things needed to make that pipe function to it's peak performance. There's more factors than you can shake a stick at involved in your graph. Great you got gains but if you could get 30% from just a pipe there wouldn't be much need for stiffer reeds,bigger carb jets, domed pistons and higher octane fuels.

 

[jar944]

3mm of stroke and closed ports and a pipe. And you got 27% "I have a potty mouth"

27% you dropped a zero. Its a 276% increase

4.7hp to 13

 

[cuttinties]

27% you dropped a zero. Its a 276% increase

4.7hp to 13

Complete different engines my friend. If you want to see gains vs pipe pm me and I'll show you videos of my own work. The only difference is pipe and muffler. I'm being harsh or angry I'm just trying be helpful and share information.

 

[jar944]

Remember that although it looks like the pipe alone gained you 27% there's many things needed to make that pipe function to it's peak performance. There's more factors than you can shake a stick at involved in your graph. Great you got gains but if you could get 30% from just a pipe there wouldn't be much need for stiffer reeds,bigger carb jets, domed pistons and higher octane fuels.

I agree slapping a pipe on a stock 6400 will not get 270%.

matching the 65sx porting (call it 190 degree exhaust) and adding a pipe will get you a lot closer.

 

[cuttinties]

I agree slapping a pipe on a stock 6400 will not get 270%.

matching the 65sx porting (call it 190 degree exhaust) and adding a pipe will get you a lot closer.

There's a lot of variables and I have said that durations are key in pipe performance. Check your pms.

 

[Mastermind]

I like turtles.

 

[spencerpaving]

I like turtles.

Snappers?

 

[cuttinties]

Snappers?

Used to do wheelies on my snapper

 

[Mastermind]

Bret, you need to get to KY in Sept.

You'd have a blast.......and I'd get to meet you.

 

[SawTroll]

Case reeds and with the much larger carb that is your answer. Wwwaaaaayyyyy bigger than on a saw. My ancient CR125 had a 36mm Mukuni on it. My 120cc 3120 has an 18mm if I remember correctly. Poor motors are starving for O2 and gas.

Don't forget the muffler design - the design of chainsaw mufflers likely is the most limiting factor. It is limited how much a larger carb and more transfer capasity helps, with chainsaw style box mufflers.

 

[redoakneck]

I thought ky was closed in Sept.?? For turtle breeding season???

 

[sunfish]

A bike has to haul your ass around , chainsaws just cut wood... an stuff.