Some of you may have noticed Chad's reference to the to knife edging the crank and wondered what it meant. In stead of clouding or hijacking Chad's thread I thought I would post it here. This is a motor I am doing as we speak. This crank has been crossed drilled and knife edged. What that means is the crank has had the counter weights ground down to a knife's edge to slice through the air of the case and oil. By creating a knife edge the resistances less which means friction is less and the crank can turn over faster and easier than say it's counter partner. By cross drilling you are increasing the oil capacity to the bearings. Under very high RPMs the oil pressure has to overcome the centrifugal force and pump now hot thinning oil to the surface to properly lubricate the bearing. By adding a second hole strategically placed this ensures that at high RPMs the bearing is not starved for oil. Balance the whole assembly, add a few coatings and you have one of the best crank setups as possible.

Just thought some would like to see and know the difference.

 

This is normal crank, Notice the counter weights and their thickness.

 

Is this a 996TT motor?? How much would such a process cost? what are the power gains or any other gains from this process?

 

Knowing Stephen he probably just put the kids to sleep ran out, and took his outta his car J/K
Evan

 

This is not a 996TT motor, but the lower end looks almost identical other than a few small changes. The cranks look identical with small journals though. The cost can be all over over the map depending on what the total job will consist off. Typically cross drilling is not an issue until you run 8K RPM. The HP gains are more those of efficiency and hard to measure. Balancing and coatings are also hard to measure results. What you end up with is a very smooth and fast revving motor able to sustain high RPM without starving the bearings for oil. The cross drilling is a double fold issue because your valve train will not cope in stock mode as high as the benefits of cross drilling. The knife edging and balance though do have daily benefits and make for a nice motor. All the work we did to this crank ran about 800.00.

 

LMAO....Nah that is about 20 hours of work to get down their. Our motors have a ton of stuff to pull off. The cams are rather tricky, not any worse than say a standard 911. The tools alone cost me 2500.00

 

Very clear pictures and I can imagine the effect on rotational resistance being improved - but I'm wondering what effect the knife edge machining has on the torsional resonance of the crank ?

From my F1 days the design of a crank which didn't fly apart due to some torsional harmonic resonance or other was a very exact science with some closely guarded trade secrets - that's V10's for you at 17,000 + rpm

I've attached a photo for your amusement - have a guess what sort of engine used to get 10 of these babies !

 

Didn't take enought time to frame this shot....

FYI This piston is defective - so I collected it as a 'trophy'.

 

Wow, I can only guess what that was out of.


We have these things balanced as an assembly past 10K when we do them to ensure that harmonics is not an issue. So far that has not been an issue.

 

That is a series of SERIOUS pockets...What is it out of?

 

Not many people can - in fact you're one of a very few who gets what this piston is all about - as for the alloy it's made of, that's another story....

More clues tomorrow ;-)

 

Tim,

Got any pics of your car? I'd love to see some more pics of cobalt blue on a 996 TT.

Kevin

 

This is interesting, I thought knife edging only involved the leading edge of the counterweights, not the outer edge.
The piston has a single extremely narrow single compression ring. It appears to be over a 4" bore very short stroke engine. The wrist pin is right against the oil ring so it must be a long connecting rod super high RPM engine. I wonder if the long distance between the compression ring and the top of the piston ring indicates a turbocharged engine (CART)? I would think a turbo'ed motor would have 2 compression rings(?) It also looks like a design for the largest possible valve sizes. Maybe from a F1 about 5 years ago?

 

timf,

Is that piston from the old JUDD motor?

 

ebaker - congrats. You are correct F1 from 96 season, so actually over 7 years ago. Non turbo of course and from a very hi revving engine - better not say which make ;-) But it's not a Judd.

Clearly you know your engines - I'll have to dig out something a little more obscure next time...

For Accomplice / Kevin - here's a picture of my TT - if you'd like anymore, let me know.