grooves cut in crank, 24% gain in hp, anyone in the know

[89sandman]

was checking out the article in snowest about how they are cutting viens in the crank of 2 strokes and gaining almost 25% hp. anyone heard of this or better yet had it done??? for the $350 per cylinder would be the cheapest way to gain around 36 horse and should be VERY reliable. anyone???

 

[2XM3]

Don't know, my good friend builds the formula 1 2 stroke motors for Mercury marine, We talked about it the other night, he asked me if I would like to buy a bridge in Brooklyn......lol......24%?? yeah.sure.
In all honesty I would have to be standing there turning the knobs on the dyno myself to believe that. Maybe some small gain at best. And believe me the boys at merc do a little bit of 2 stroke research.....lol...


Anything is possible but come on now......24%?? IMHO

 

[nickracer9]

I've heard of this in R/C engines. Think it's called a turbo crank.

 

[spring snow hero]

the "turbo crank" has been around since I had my new 1981 yz 50.....in 1981. might help a touch in a very rich fueld engine, but mostly a pipe dream IMO

 

[2XM3]

Found this:

Quote"

The term "Turbo-Crank" refers to a modification to the crankshaft of a two-stroke engine, whereby scoops are fastened to the crank in order to improve the volumetric efficiency of the engine. Every decade some hop-up shop revives this old idea and gives it a trendy name with product promises that it can't live up to. These crank modifications cause oil to be directed away from the connecting rod and often times the vanes will detach from the crank at high rpm, causing catastrophic engine damage. My advice, don't waste the $750!

 

[spomey]

Now Way 24%, Ive also heard of "sharpening the crank" where the leading and trailing edges of the counter weights are knife edged to create less drag when spinning some balance shops provide this service but IMHO 24% is streaching it.

I have a CR500 that I will send my crank in to have it balanced and weighted (16 oz) and I may have this "sharpening" done also. I wont know if it works or not other than to just say I did it though.

spomey

 

[Freak]

also know as knife edge cutting of the crank. It could easily give you 24% on the low end but you will some top end inertia. They do it on bullet bikes a lot to help them come out of the corners quicker.

 

[snow_knight]

have done this to many of my motors... never actually dyno'd after done.. however there is a big difference in low end torque and never seen any loss on the top end.. dont agree with the 24% though.. It is fairly expensive.... but then again.. what on a sled isn't???

There is lots and lots of motors out there in the racing world that have it done to stock motors...

 

[likkerpig]

I want to see an independent source go in with a stock motor, dyno, perform the mod, then go back to the same dyno and show me the dyno sheets. If this mod has been around forever, don't you think any of the big 4 wouldn't have looked or experimented with it for a potential 24% increase in power for little to no expense?

 

[triple7]

One of the guys in our group had it done to his XP. Its maybe a little bit better off the bottom but darn little and there is no gain on the top. Just our expirience, could be different for others. B

But back in the quad racing days, our non turbo crank motors were never whooped up on by turbo crank motors. I just dont believe it works.

 

[1Mike900]

I wonder if Cat did this to the 800 crank? Besides lightening it, Maybe they knife edged it and drilled little holes all the way around the edge of the crank throws? Know wonder it is 18 BHP stronger? Yeah right!

Mike

 

[snoman159]

I would think at great crankshaft speeds you would get a "golf ball" effect where there would be a low pressure zone in the scoops. Essentially you'd have less aerodynamic drag like a golf ball does, but this does nothing to help more air through the motor. Besides that I have a hard time believing a 25% gain in volumetric efficiency since most stock motors are close to 90%, and its not uncommon to see volumetric efficiencies over 100% (even without forced induction). Besides that a 25% gain in volumetric efficiency wouldn't necessarily result in a 25% gain in power outpt. Combustion efficiency is a whole other ball game altogether.

The lower end gain may be justified by the lighter crank, with less mass the motor is going to spool up quicker because less work is needed to get the mass of the crankshaft rotating. Call me a skeptic...

 

[machineman]

t-crank

Hey, there is a resession happening and they need to generate income too!

 

[Ove]

Every time I open an engine I am thinking that the webs are way too close to the case, going about 135 cycles a secound and the outer surface of the crank has about 80 miles an hour something must be going on in there. maybe it is vacum only around the crank.

 

[NoSecondChances]

Is this what you are talking about?
http://www.snowest.com/forum/showthread.php?t=142419

NSC

 

[hatchers]

also know as knife edge cutting of the crank. It could easily give you 24% on the low end but you will some top end inertia. They do it on bullet bikes a lot to help them come out of the corners quicker.

Engrish? What kinda smoke you cracking....

On the topic, a simple spark plug gap recalibration will give you results of near 50% increase in HP, ive seen it done and took down the freak shortly after this

Dont be fooled with those cheapo Inside mic shims to set the gap, oh no, you need that chit under a scope, something you can see mars with would be good enough

 

[framus]

daa case too

Seems to me that you'd also have to look at how well the case itself evacuates or flows.

 

[Fredrik]

Anyone tried speedwerx crank on cat not turbo crank just lighter does it reduce engine vibration.

 

[gus bohne]

Please,
NO change in the outer surface of the crankwheels in a 2 cycle engine will show one bit of power increase OR decrease..

Crank MASS does affect vibrations FELT as well as polar moment of inertia,
changes to crank mass can deaden vibration and SLIGHTLY effect response to CHANGE in rpm,that means both up and down rpm swings.

Reducing crankwheel diameter WITHOUT like changes to maintain crankwheel to case clearance will lower case compression and create large pools of unatomized fuel that will cause fluctuating fuel curves.

In 23 yrs of 2 cycle work No gain has been made in texture of the surface as crankwheel rpm is very very slow and will NOT cause ANY pressure change in the cases.

IF it did would it not be exactly the same as supercharging a 2 stroke? how well does that work ??? IN THE REAL WORLD THAT IS<<<<!!!

supercharged 2 strokes have always had an exhaust valve OR have been designed with an extremely low BMEP so as to NOT make enough scavenging to effect the LOW pressure boost of the supercharger.

Changes to the shape of the OD of the wheels (full circle vs pie cut )......
Pie cut cranks may look like they FLOW to the transfers of a case fed engine better at near bdc timing but ,,,,,,
The real FELT change is in the POLAR MOMENT.. mass being equal, the gain in acceleration is due to the moment of inertia,,,,,nothing else..

Sorry if I burst the hopes of some newbies,, welcome to reality !! LOL

I can elaborate further if this ever comes off a dyno showing ANYTHING LOL


2 questions for you guys to ponder.

1. how do we measure transient power changes ?
2 will I notice anything from it ?


I'll check back in and see how we do..

Gus

 

[DWHalverson]

IN THE REAL WORLD THAT IS<<<<!!!

You forgot Gus, this is cyberspace.
If you believe, then it's true.