Turbo Crank

[StrongBad]

Hey to all the saw builders, I was wondering if anyone has experimented with turbo cranks? They have been used since early 80s and supposedly perfected for motocross, but with onset of 4 stroke push by oems it lost its efforts.
It involved cutting grooves or machining scooped holes into crank to act as a charger to push mixture through crank case faster. I am not good with uploading pics but basic google search of Turbo crank shows what I am talking about.
I think it would be a good thing to experiment with on saws as it seemed to work best with mini motors on 2 strokes.

 

[StrongBad]

 

[legdelimber]

I wonder has anyone tried this on some crankcase stuffers?
You'd need to polish out and get rid of any stress raisers from cutting things, so as not to make a grenade out of them.

Back in the mid '70's, I had started a sketchbook with the idea of some slotting to be something more like a radial fan. Who knows why I never tried a few of the ideas from it? Too ADD I guess.

 

[Marshy]

Hey to all the saw builders, I was wondering if anyone has experimented with turbo cranks? They have been used since early 80s and supposedly perfected for motocross, but with onset of 4 stroke push by oems it lost its efforts.
It involved cutting grooves or machining scooped holes into crank to act as a charger to push mixture through crank case faster. I am not good with uploading pics but basic google search of Turbo crank shows what I am talking about.
I think it would be a good thing to experiment with on saws as it seemed to work best with mini motors on 2 strokes.

I'd like to see an actual study that shows that adds power. I dont see it, but thats just me.

 

[Nutball]

Should help increase pressure around the crank and decrease it around the shaft area. Probably another minimal gain type mods only worth trying in a race. I have done it before on a .09cuin RC plane engine. I don't know if it helped.

 

[StrongBad]

There is a site on dyno tests that showed gains on a kx500. Definitely mixed opinions out there on subject. Also fact that factories have never used it in production.
I am sure testing varied in results due to dozens of approaches in design in machining. I would think a blank sheet/fresh start with a crank acting more as a turbo compressor with transfers designed around it would be a cool experiment. A crank case built around a crank with compressors on each side facing rod with really large transfers that form around compressor wheels, perhaps case induction port instead of on cylinder.
I don't know....bored at work brainstraining haha.

 

[cus_deluxe]

Talked to an old timer snowmobile builder/mechanic i know and he mentioned these just yesterday. He said he knew a guy that had a dyno and that had messed with this idea on vintage single cylinder race sleds. Said the difference didnt really show up on the dyno, more of a “ seat of the pants” type feel. For whatever thats worth haha. I see full circle or stuffed crank having more effect on a saw engine.

 

[bwalker]

I'd like to see an actual study that shows that adds power. I dont see it, but thats just me.

You wont, because turbo cranks dont make more power.