Any advantage to knife edging Cranks?
Race only application.

 

Every good high end race crank is knife edged........thats gotta tell you something.

 

Crank profiling is key to reducing windage. Also reduction in counterweight area is good. You then go back with mallory metal to obtain proper balance.

 

Nowadays few cranks are completely knife edged as most are bull nosed on the leading edge with a trailing knife edge though. Every little bit helps.

 

About to make this decision myself. I will get a quote from the machine shop and if it is in the $200 to $250 range I will probably have it done. Every horsepower counts when you are trying for 400RWHP with a 355 gen one L98 small block.

 

Thanks guys, I'm looking at getting a 4" eagle crank and just have it knife edged.

 

Crank work is not the most fun you will ever have that's for sure. I agree with Eric, bull nose on the front and knife edged on the back along with what Curtis said turn down the counterweights and throw some Mallory into it.

Bret

 

I think you'll find that its cheaper to buy a crank already done the way you want it from Eagle, Callies or whoever, than to pay someone to modify one you already have and then re-balance it. Most shops around here charge $200+ just for the balance job alone.

 

You might as well go ahead and spend even more money on a good oil pan with a big side kick-out. Its worth 10-15 hp.

 

Dry sump

 

Yeah, i may just end up doing that. I was initially looking at the Scat Custom Billet... but at $2500+ .

Thanks again for the feedback guys

 

Coat the crank and the rods with oil shedding coating.

 

I guess the million doller question is when does it become worth it to knife edge the crankshaft and what horsepower gains are seen? If you have a motor that does not turn above 6200rpm is it worth it? If you have a deep sump oil pan to keep the oil away from the crank and a good windage tray is it worth it? If I knew I would see a 5hp gain or more than I would say it is worth it. If one or 2 horsepower than no.

 

If you are in a competitive racing class and spending $15-30k for your engine, it is probably worth it. If you are doing a $5-10k upgrade for street/strip bracket racing, probably not.

 

Look at compartmentalizing the block into four sections at the main caps with the dry sump pan. Cup engines do it with substantial power gains at very high rpms. The equipment is probably not available off-the-shelf however.

"...how fast do you want to go?"

 

between my sons braces, my daughters wedding this summer(talk about a scam)....... I'm pushing the car making engine noises.


Interesting concept on compartmentalizing.

 

The more stroke you have and the more RPM you turn the more it helps.

Bret

 

7 HP in back to back testing of a 305 cube econo sprint engine making just shy of 500 HP @ 6900. This was with a Scat cast steel 3.500" stroke out of the box. Switched to identical crank that had been profiled in a CNC. Bullnosed on the front, knife edged on the trailing edge, and counterweights turned down for a no drill balance job. The test was done at 300 rpm/second.

 

Just got a quote from Lopez Crank to do the "airplane" style knife edge on my crank for $200. I would think is the same a bullnose leading edge and knife edge on the trailing side. This will be on a 355 only turning maybe 6200rpm.

For that price I might just give it a go. Joe Racer was the increase mainly in the upper rpm range or across the board? Thanks

 

There was increase throughout the pulls, but as you would expect, it was the greatest at the last 1500 rpm. We start the test at 4200, and run it up to 7500. I would imagine that a motor with a longer stroke and no rules restrictions would show a better gain. I would also say that our results may not be typical..... our profiling isn't just a bullnose and a knife edge. There are offsets and tapers involved. We wanted to try to direct the oil where we thought it should go.