Has anyone done this before? Does it work?

At the very least losing some rotating mass will be a benefit.

Is this something I can trust to the same machine shop that's doing my block and head or is it more specialized then that?

Does anyone think (or know) there would be a problem with knife-edging a crank for a turbo application? What limitations would a crank have afterwards?

One more thing... Are there any good sources for forged pistons or another piston that would be suitable for a turbo /. By good I mean quality part at reasonable price.

Thanks everyone

W

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Grip it and rip it

Hi,
can´t help you with your questions but I do have a picture of a really light /6 crank on my hdd. So it has been done Send me an email so I can send you the pic.
duster72198@aol.com
Later,
Chris

It's probably not worth it unless you're going to be turning some really high rpm. Done right, I don't think it affects strength significantly. Most people with turbo motors don't spin them very high, but instead let the torque do the work. I'd imagine you won't be turning it much past 5500. If that's the case, I'd skip the knife edging and focus on a good windage tray.

I think reducing rotating mass can´t hurt anything. Engine will rev up faster, the car will accelerate slightly faster. But having the crank cut and balanced will be quite expensive I think. Unless you have a brother or friend who´s got a machine shop, or even can do the work all by yourself, this is an all out racin modification. There are definatly parts the money is better spent on. Don´t know how much weaker a cut crank is, too... in the long run.
But hey I´d like to have such a piece in my engine anyway

A knife edge crank is something i'd take the time out to do. it'll help alot as it "cuts" through the oil better freeing up some extra hp, this is all the little "nit-pick" stuff you have to do to save everybit of HP

you can grink it yourself then take it into a shop and get it ballanced, do a search on this site for "cranks" or "crankshaft" and you'll find something, maybe Doug Dutra will chime in here because he's done it before i belive

Justin

I've seen a dyno report somewhere (unfortunately, I don't remember where) that showed very little gain from knife edging. The gains would only be even less on lower-rpm motors. True, reducing rotating weight is good. The question is whether or not it's worth the gains in this case. If it is, is knife edging the best way to reduce it? Things can be done to cranks to cut weight out that don't involve knife edging. Also, if the pistons and rods are too heavy to balance with the lightened crank, guess what you do next? That's right-mallory metal. If this happens, you have just spent a lot of good money to cut weight from the crank so you can spend even more to add it back. Don't believe me? Call a few machine shops and price mallory metal. If the desire is to reduce windage, there are better ways to do that. Like I said before, a good windage tray will help a lot there. Think about it-would you rather spend lots of money getting a crank knife edged to cut through oil better, or would you rather eliminate excessive airborn oil in the first place? My vote is on preventing the problem in the first place. You may wonder about air resistance. Surely knife edging will help that? I'm sure it would. But, eliminating excessive airborn oil should help much more. Why? Well, oil doesn't float when you open a container of it, does it? That's because it's heavier than air, or has more mass to be specific. That being the case, the comparatively heavy oil will impede the rotation of the crank far more than air will, and can be more easily controlled via windage trays and crank scrapers than air can be controlled by knife edging. If you really want to reduce rotating weight, put smaller and lighter pulleys on the crank and accessories. Use a lightweight flywheel or a small diameter torque converter. While you're at it, get an aluminum driveshaft. Anything that has to rotate to move the vehicle should be lightened. That includes the wheels, which also has the added benefit of reducing unsprung weight-another BIG benefit when it comes to how the suspension behaves. Of all the places to reduce rotating weight, in the case of a (presumably) low rpm turbo motor, the crank is about the last place I'd look because of the cost of knife edging and the possible resulting cost of having to either buy expensive light pistons or add expensive mallory metal. Take it from someone who's been there, there are cheaper and better ways to gain power first.

I rec'd that picture from 72duster and that is some piece of work. I don't know how to put it up here for all to see but you could slice a roast beef with this thing (could probably slice the whole cow).

I'm guessing this would be significantly lighter than stock. I still think I want to pursue this (at least in theory). Knowing what it's supposed to look like when it's done helps a lot too (thanks Chris).

If anyone can tell me how to post this picture I'll get it up here

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Grip it and rip it

Is this the photo you are looking at?



The Cox Boys had a couple of these done a few years back, both are now cracked and not useable.

I agree with 440V8 that doing a balls-out knife-edge job is not a good use of time and money.
BUT, taking time to grind all the rough edges off the SL6 crank and remove some non-structural weight will help a race engine.

As for the light piston availability, this is a non-issue with a Slant Six, the crank is neutral balance, no "bob-weights" needed like a V8. The SL6 crank can be balanced by itself. (I include the flywheel / flexplate and balancer) Pistons and rods can be any weight, as long as they are the all the same weight as a matched group.

I can safely take about 10 lbs off a SL6 crank without much problem, any more then that hurts the structure and leads to cracking.
DD

I had a good talk with my machinist today, he hadn't seen my mill put together yet.

He recently did another hi-po slant for a 66 Barracuda, the engine needed a crank kit, but he forgot the pre-67 rule. So in the end he had a 1966 crank kit and a 1968+ crank kit laying in his shop, just for curiosity sake he checked the balance of both cranks and they were dead-nuts equal....
(Should've played the lottery that day).


Pretty interesting about how well these cranks are neutral balanced...

-D.idiot

Okay so I think we'll shelf this idea for now and move on to something else. I don't mind spending the money to achieve the gains but if there's a lot of $$$ and not as much performance gain then it ain't worth it.

Thanks a lot for the good info.

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Grip it and rip it

Wouldn´t it be a good idea to have some kind of gallery for pictures of slant six engines, parts, modifications ? I have collected some pictures from .org and .com (remember the good old .org forum when there was a *pic* sign after each post containig one ). I often look at them when I´m thinking about this and that, and have sent many to people like welly225 looking for info.
(copyrights?)
What do you think ?

Sounds like a great idea if there is enough server space. As far as copyrights if you give credit when you know the photographer or post it when someone claims it you are probably good!

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It is easier to REACT,
than it is to THINK!

Middy.