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2 Stroke theory in relation to chainsaws

junkman

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There is a lot of info on 2 strokes out there ,but most relates to bikes and sleds ,how much is transferable to saws when doing mods ?
 

Brush Ape

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The part about an engine working like an air pump. And the part that means you need fuel/air, compression and spark at an exact time while lubrication keeps metal parts isolated and incapable of increasing friction. A chainsaw needs a sharp chain might be one primary difference.
 

exSW

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Doesn't a dirt bike operating over a broader rpm range than a saw make the biggest difference?
 

Nitroman

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As long as you are referencing air-cooled engines, all of it, excepting the expansion chambers dirt bikes have.
 

skidooguy

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Bikes and sleds use exhaust power vales or variable power valves to help bottom end power is one of the major differences to me. I often scratch my head wondering how a tiny saw motor makes that kind of power.
 

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Bikes and sleds use exhaust power vales or variable power valves to help bottom end power is one of the major differences to me. I often scratch my head wondering how a tiny saw motor makes that kind of power.
There's not nearly the same power to cc ratio in a saw compared to a bike or a sled. 60cc saw puts out 4 or 5 hp. 600cc sled puts out 120ish
 

Nitroman

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There's not nearly the same power to cc ratio in a saw compared to a bike or a sled. 60cc saw puts out 4 or 5 hp. 600cc sled puts out 120ish

Yes, but, if you take the saw motor, slap on a tuned pipe and a carb to match, she'll make the power. The tiny carbs are what kill power for a saw.
 

skidooguy

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I understand. It just seems so small I find it impressing. I am used to a 800cc Rotax so a saw motor just seems so small in relation. What are the new 600cc sleds claiming for horsepower these days just curious.
 

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Yes, but, if you take the saw motor, slap on a tuned pipe and a carb to match, she'll make the power. The tiny carbs are what kill power for a saw.
I suppose it still is impressive if you look at how small a clamshell motor is (being fully self contained) and the power it puts out.
 

huskihl

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I understand. It just seems so small I find it impressing. I am used to a 800cc Rotax so a saw motor just seems so small in relation. What are the new 600cc sleds claiming for horsepower these days just curious.
Not sure. 500 indy in the early 90's was 87. So now it's 100. 600cc is prolly 120 to 130
 

skidooguy

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That's pretty awesome. My last 700 only had like 110 or so. My carbed 800 claims a little over 150 hp but who knows at my elevation.
 

Deets066

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Bikes and sleds have way longer stroke, which changes a lot. Most of the tricks that work on bikes and sleds don't work for saws.

I would say throw out everything you know about bikes or sleds when it comes to modding a saw motor.
 

skidooguy

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That is a good question that got me thinking about it now junk man. Lol. Maybe I'll have to tear down my bike and saw next to each other.
 

skidooguy

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Right on deets I would love to dyno my turbo sled at elevation just to see what it's laying down.
 

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Won't a bike and sled have different power curves because bikes are gear drive and sleds variable drive?
 

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I understand. It just seems so small I find it impressing. I am used to a 800cc Rotax so a saw motor just seems so small in relation. What are the new 600cc sleds claiming for horsepower these days just curious.

Ski-Doo 600 H.O. 130hp. Pol 800 running 180 as are AC and Ski-Don't. But these are computer motors where everything, even the oil pump are driven by comps. Carbed are down 135 hp for 800 Polaris.

If you read radio-controlled boats, a guy who wrote an article about his testing a 35cc motor with changing the pipes dimensions was getting around 12hp at near 20k rpm. So it is comparable.
 

Deets066

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Ski-Doo 600 H.O. 130hp. Pol 800 running 180 as are AC and Ski-Don't. But these are computer motors where everything, even the oil pump are driven by comps. Carbed are down 135 hp for 800 Polaris.

If you read radio-controlled boats, a guy who wrote an article about his testing a 35cc motor with changing the pipes dimensions was getting around 12hp at near 20k rpm. So it is comparable.
Try running 87 octane in a saw that has 200 psi comp and then a sled that has 200 psi comp and tell me how they compare.
 

jacob j.

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Bikes and sleds have way longer stroke, which changes a lot. Most of the tricks that work on bikes and sleds don't work for saws.

I would say throw out everything you know about bikes or sleds when it comes to modding a saw motor.

Plus much longer intake tracts, larger mixing areas in the crankcase, longer rods on the crank, larger and longer transfer tunnels, etc. I've cut down a couple of older motorcycle pistons to use in saws but it was much more work than it was worth.
 
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