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Discussion Starter · #1 ·
Some freinds of mine dominated the modified mini stock class at the local speedway for many years. They used a de-stroked Datsun 4 cyl. L-series engine, with a knife-edged crank, and a few relatively low cost tricks to acheive a very fast and reliable setup. I want to do the same thing, only with two extra cylinders and a turbo. I think this should result in an engine that revs very fast, and very high. This will cost a fraction of what a 3.1 would cost to build aswell!
*****Here's a little background on my theoretical bottom-end setup:
*L28t block
*knife-edged 240 crank
*race prepped 240, 9mm rods
*custom forged pistons (similar to 240sx, w/ different pin height to acheive 8:1 CR)
*Arp bolts, head studs, Hks 1mm head gasket, etc etc.

If anyone has knife-edged a z crank or has some knowledge about the subjuct, please drop in your 2 cents worth!
Tony Rohn
PS see you V8 guys at the races!!!!
 

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seen a few knife edged cranks in Japan. It's pretty straight forward, and any good racing machine shop should be able to handle the job. It's worth 5-10 hp, so I'm told, but the Japanese speed shop that did the work said they got similar results with a good crankshaft scraper and polishing the counterweights. Apparently the knife-edging helps the crank "cut" thru the oil as it sloshes to the back of the pan during drag racing starts.
 

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RE; My vote is no.

I woudn't do it. I discussed this with my engine builder, when I built my 3.1. he had built and raced many L6 motors, and when he did that, he found only a hp or two for that motor, at best, maybe 3-4. for the cost of the knifing, you really gain very little. It is definatly not a good mod, for you are taking away the counterweights, possibly adding harmonics which rob some power. now, some would say my builder doesn't know how to balance, to which I say BS, for my stroker motor is one of the only ones out there that produces serious power all the way to 7000 rpm. And i attribute most of that to the balancing job. i have a mild cam,(460 270/280 split duration), and 40mm carbs.
anyways, i am getting off the subject. my vote is no, especially looking at the cost to gain ratio.
-Bob Hanvey
73 240 3.1
 

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Knife edging is not the thing you want to do. There was some discussion on this awhile back. Try searching the archives, it may still be there. Don't spend your money on it. There's more bang for the buck elsewhere.

Ken
 

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Discussion Starter · #5 ·
RE: KNIFE-EDGING More Q's

To give you an idea about why I want to do it: I want to acheive, high rpm's in a hurry, and to spool up my turbo fast. My mini-stock freind says that this mod helped them get their RPMs up higher than before they knife-edged the crank and get it there alot quicker. Almost all powerful race engines have lightened internals, and I wanted to try and do that on a budget. Tony d; you mentioned a crank scraper and polishing the counterweights, what is a crank scraper?? Bob H; I assumed that knife-edging the crank would improve harmonics, as that was a concern of mine. What can you do to improve harmonics, and remove some weight in the engine without springing for expensive rods, or an astronomical billet crank or something. Also, I'll admit that my knowledge about building HP is limited, and I am learning, but I was uder the impression that you could lighten things up and change the responce and character of an engine without getting alot more horsies (ie: lightened flywheel) I want to learn more and clear up any misconceptions I have, so school me guys!! Thanx!
Tony Rohn
 
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