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The mkiv Supra Owners Club

Knife edging the crank????


johnd-mkiv
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If your cranks out, why not? Gains are probably minimal but it's directionally correct.

Not sure if this is true for Supra engines, but generally speaking.

 

The £380+vat bill that comes with it, if its not worth doing ill spend it else where. The crank will be balenced either way

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In any engine, oil is always draining down into the pan from the top and being sloshed back up from the bottom. When the counterweights on your crank hit the oil, you get loss of power. In addition, you also get loss of power just from spinning the heavy crankshaft around. Knife-edging will reduce power lost from hitting the oil and also takes off several pounds of weight from the crank. You get higher RPM and better reliability.

 

The first bit about the crankshaft hitting oil particles in the crankcae is correct. Knife-edgeing (or "blading") the crank can have a measurable effect in reducing parasitic losses from this (known as "windage losses").

 

I'm not so sure about the power loss from just spinning a heavty crankshaft around. Because the material removed will be at the extremes of the crankshaft counterbelence weights, there will be a measurable reduction in inertia, so the engine should accelerate a little bit faster. I think its debatable whether this would be noticable, especially if you still had a stock flywheel hanging off the back. % wise the inertia reduction for the entire cranktrain would be pretty small.

 

As for higher RPM and better reliability, you might get a slightly higher RPM, but beter reliability you definately won't. Taking mass off your crank will reduce the in-bay primary balance and affect your oil film thicknesses. Its usually hard enough getting sufficient mass into a crank counterbalance that there is unlikely to be excess material there that can be removed willy-nilly.

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The GM L850 2.2 and 2.0 litre engine series all have knife edged cranks, so its on "cooking" engines, too.

 

Don't get me wrong - its a really neat feature if its designed in from the word go, but it can be difficult and the benefits are marginal so a lot of OEMs don't bother.

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Don't most of the mental power guys in the US use stock cranks. If so it does not seem to slow them down ;). In my VWR race engine good for (USA) 1000RWHP the crank is the only stock moving part.

 

Given what has been said, if the engine is in bits anyway, you may see very small gains, however the same money spent on turbo mods may see higher gains. Given the choice I wouid go for turbo modifications.

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