Piping a saw engine

[tolman_paul]

I know there are probably allot more guys that would like to slap a pipe on their saw for a GTG or just for the heck of it, but don't want to drop the coin on a custom pipe. All well and good, but I thought I'd drop an idea for a more reasonable way to get a pipe for your saw. There are lots of old dirt bike tuned pipes that can be had in the $25-50 range on fleabay or from a local salvage yard. They may need a dent or two pulled or pounded out, you'll have to fab up a header, and likely make a few cuts to reconfigure the pipe the direction you want, but it's a cheap power boost. I'd say most 1990 and later pipes are well designed and will likely have you most of the way there to an ideally designed pipe.

Here's a 50cc pipe for a Polini

60cc pipe for a Kawasaki

80cc pipe for a Honda

There are also 100cc pipes for karts and 85 and 125cc pipes for bikes. Do some fleabay searching for various bike brands Honda, Suzuki, Kawasaki and Yamaha and you should be able to find a pipe that can be made to work for your saw. If you're looking for a 40cc pipe the good Italian pocket bikes use 40cc engines but finding one of those pipes used is going to be a tougher search.

 

[chainsawwhisperer]

 

[user 64030]

Interesting idea, but (and I have no clue here) would the pipe be tuned the same? Meaning would the 80cc bike motor have the same rpm range/powerband as an 80cc saw? I would thing with the gearing of a motorbike tranny, and given the weight they need to move the pipe might be tuned differently.


But like I said what do I know???? :confuse:

 

[MechanicMatt]

opcorn:

 

[BloodOnTheIce]

I know there are probably allot more guys that would like to slap a pipe on their saw for a GTG or just for the heck of it, but don't want to drop the coin on a custom pipe. All well and good, but I thought I'd drop an idea for a more reasonable way to get a pipe for your saw. There are lots of old dirt bike tuned pipes that can be had in the $25-50 range on fleabay or from a local salvage yard. They may need a dent or two pulled or pounded out, you'll have to fab up a header, and likely make a few cuts to reconfigure the pipe the direction you want, but it's a cheap power boost. I'd say most 1990 and later pipes are well designed and will likely have you most of the way there to an ideally designed pipe.

Here's a 50cc pipe for a Polini

60cc pipe for a Kawasaki

80cc pipe for a Honda

There are also 100cc pipes for karts and 85 and 125cc pipes for bikes. Do some fleabay searching for various bike brands Honda, Suzuki, Kawasaki and Yamaha and you should be able to find a pipe that can be made to work for your saw. If you're looking for a 40cc pipe the good Italian pocket bikes use 40cc engines but finding one of those pipes used is going to be a tougher search.

Adding a pipe that hasn't been built to match the RPMs, porting, and fuel of the saw is just a noise maker
you'd be money ahead just leaving you muffler off.

 

[chainsawwhisperer]

Adding a pipe that hasn't been built to match the RPMs, porting, and fuel of the saw is just a noise maker
you'd be money ahead just leaving you muffler off.

Could Keith add a dirtbike pipe to one of his stereo systems to make it louder?

 

[Ironhand]

I say try it. It should be a cheap and relatively easy experiment. In my "free" time, I restore 1970s 2-stroke street bikes. When those bikes were new, expansion chamber technology was just coming online and they had only a conventional exhaust. All of those bikes (Yamaha RDs, Kawasaki H1, 2, etc...) respond VERY nicely to an exhaust upgrade. Tuning required, of course.

What sort of exhaust are the saw-engined kart guys running?

I'm picturing a 20+lb 100cc Mac with cackling out of an unmuffled huge exhaust...:chainsawguy:

 

[Scooterbum]

Seems to me it would be relatively close, not exact mind you but close enough for someone to have fun with.

All the 2-smoke dirt bikes I've ridden have had the power band in the upper rpm range, so why wouldn't this work for a saw?

 

[Arrowhead]

Adding a pipe that hasn't been built to match the RPMs, porting, and fuel of the saw is just a noise maker
you'd be money ahead just leaving you muffler off.

Yep. I've built pipes for saws before, lots of things to consider.
I'd say adding a pipe not specific to the saw will hurt the saws performance.
Just an inch +/- in the belly or stinger can make or brake it.

 

[blsnelling]

I say give it a whirl. Go into it expecting the worst and you might get surprised. Yes, pipes are built to exact specs for a given engine, tuned to the volumes and porting times, but I've seen some crazy stuff work pretty good. What comes to mind is an older gentleman that used to run the shop near Erick. He did some pretty unconvensional stuff and it didn't work too badly.

 

[HELSEL]

I say give it a whirl. Go into it expecting the worst and you might get surprised. Yes, pipes are built to exact specs for a given engine, tuned to the volumes and porting times, but I've seen some crazy stuff work pretty good. What comes to mind is an older gentleman that used to run the shop near Erick. He did some pretty unconvensional stuff and it didn't work too badly.

I would also agree with that, One
of the down falls on the bike pipe
is the weight. Some things that
shouldn't work turn out to be the
fastest sometimes.

 

[blsnelling]

I would also agree with that, One
of the down falls on the bike pipe
is the weight. Some things that
shouldn't work turn out to be the
fastest sometimes.

+1. It shouldn't work well, but it might. You won't have much money or time invested in trying it out. If nothing else, it'll sound cool and be fun to run.

 

[tolman_paul]

As I tried to state, it's a starting point and I think you'll find that you'll be much closer to a good design than completely out of the ballpark. You'll need to figure the length for the rpm you want to make peak power at which you might add at the header, or you might cut the mid section to lengthen or shorten the pipe. But as far as the pipe volume and cone angles, it's going to be in the ballpark and will give much better performance than a muffler.

I'd be curious how many saw builders make up 1/2 dozen different pipes and do pulls on a dyno to compare the performance, I'm thinking very few. Most likely use Gordon Jennings formulas and call it good. Given that saw engines run essentially at a single rpm and have relatively sedate port timing, they are fairly tollerent of pipe design.

 

[troutfisher]

Might be able to get some gains from a bike pipe. For a gas saw turning 11k or so in the wood try 23-24 inches from the piston skirt to the center point of the reflector cone for a tuned length.

 

[HELSEL]

As I tried to state, it's a starting point and I think you'll find that you'll be much closer to a good design than completely out of the ballpark. You'll need to figure the length for the rpm you want to make peak power at which you might add at the header, or you might cut the mid section to lengthen or shorten the pipe. But as far as the pipe volume and cone angles, it's going to be in the ballpark and will give much better performance than a muffler.

I'd be curious how many saw builders make up 1/2 dozen different pipes and do pulls on a dyno to compare the performance, I'm thinking very few. Most likely use Gordon Jennings formulas and call it good. Given that saw engines run essentially at a single rpm and have relatively sedate port timing, they are fairly tollerent of pipe design.

Yes most of the top builders
try several different pipes.As
far as a dyno most just use
the sawing block.

 

[mactodd]

I say try it. It should be a cheap and relatively easy experiment. In my "free" time, I restore 1970s 2-stroke street bikes. When those bikes were new, expansion chamber technology was just coming online and they had only a conventional exhaust. All of those bikes (Yamaha RDs, Kawasaki H1, 2, etc...) respond VERY nicely to an exhaust upgrade. Tuning required, of course.

What sort of exhaust are the saw-engined kart guys running?

I'm picturing a 20+lb 100cc Mac with cackling out of an unmuffled huge exhaust...:chainsawguy:

I don't know... do you think Toomey or Denco would weld up one for my SP125C?

 

[greg409]

It's funny, last week I was looking @ 60cc bike pipes for my SXLAO, I've got the means, if I just wasn't so darned lazy?

I think the pipes start to work aroung 4-5K rpm - near the top of my Homelite..............

luck,greg

 

[MechanicMatt]

My first response was opcorn: because I didn't want to respond and have you guys think I was crazy or stupid or nuts. Truth is Im a bit crazy, have been known to do stupid things on occasion and lots of things drive me nuts. BUT I have a pipe that was built for a little 50cc dirt bike and with my mig welder I cut and welded this pipe to work on a Poulan Wildthing. It sounds freaking awesome but, I don't race and never have so Im not sure if its "faster". I just made it because it looks AWESOME and SOUNDS even BETTER, Im scared to run it too too long because its so LOUD I can't hear the "4 stroking" so Im not sure if its tuned right. If anyone one of you are going to Spike60's GTG Ill bring it along. I usually leave it off the saw and run the modded muffler, its easy to cut firewood that way. But if anyone is interested in seeing it, I'll bring it.