knife edge crank

[ablesnead]

Talk to me about knife edging a crank on a 2.8 ,,,,, I've driven a porsche in the past with a knife edged crank , and almost 6 lbs lighter ,, it was a hoot , very motorcycle like response. Dave of Rebello is not in favor of it , but I  cant really find a downside in internet discussions of knife edging ..( this is for a track car only )  any datsun experiences out there ?

[ctc]

You might PM johnc. He has posted pics of a knifed edged crank on here. Don't know if it is his engine. There are a couple people on here with knife edged cranks, you might want to search them out.

[Xnke]

I drive a half-knifed crank...the counterweights are not cut as severely as a knife edged crankshaft, but the crank came to me that way. My machinist advised me to clean up the previous guy's work and we'd balance it again. It doesn't rev much differently than the stocker with the stock flywheel, but with the 14lb unit it has a bit of a learning curve to driving again. (especially with the cam I have in the car now; I'll have that worked out shortly.)

[tamo3]

I have knife edge LD crank but not yet installed on my Z yet.

 

What I heard from Japanese folks, the biggest different you can experience on high Rev situation.

[Tony D]

Generally the. Leading edge meeting windage is also tapered to lessen losses.

[roger280zx]

What kind of crank work goes into your LSR car, Tony D?

[ablesnead]

I  like the response and feel already , just wondering about how the reliability would suffer...its effect on the 7300 rpm harmonics that I heard about , a damper should work similar to stock weight I assume

[Tony D]

What kind of crank work goes into your LSR car, Tony D?

Huh..huh huh huh, ha, ha haw haw haw haw!

 

9,500 rpms + standard balancing for that speed. Nissan Rods...

 

You can do what you want for incrementals, no LSR Z I know has a knife-edged crank in their L-Series.

 

So now the harmonic is 7,300? Or was it 7,500?

Edited April 22, 2013 by Tony D

[johnc]

Knife edging is part of the lightening process.  My LD28 crank went from 51 lbs. to 35 lbs. with a lot of surface treatment after all the machining.  We actually used two cranks because the first could not be made straight enough after Nitriding.  You will also need a good balancer like the ATI.

 

[Xnke]

How much does knife edging a crank really gain you in the overall scheme? Mine was done about half the amount that is shown in the photos here, plus a standard balance. Is the end result supposed to be lower windage loss, or lower PMOI, less torsional vibration, what?

[johnc]

The faster you spin the engine the more you'll benefit.  Is it a big percentage?  Probably not.  Its one of those small changes that, in conjunction with other small changes, that result in a big overall improvement in performance.  I see many people ignoring a 1% improvement in performance because its not worth it.  They end up ignoring ten 1% performance improvements and wonder why their car performs 10% less then the next guy.

 

FYI... the way my crank was knife edged was more for MOI improvements then windage.  My engine was limited to 8,000 rpm so there wasn't a big gain to be had from windage reduction.

[jeffp]

In my opinion, you are wasting you time efforts and money. You want a quicker throttle response, get a 11 Lb flywheel and you will be happy. That modification is is strictly for race, on a N/A engine. Also, you just may want to talk to BHK for a damper. The ATI component is expensive, and I am not all the convenienced they located the harmonic frequency of the L28 engine. Myexperience with ATI is that they really could not be bothered with the L engine seriously. Also, at the time I was speaking to them, they had no solution for bely pullies for the damper and the L engine.

 

I contacted BHK and worked with them to develop a damper that was tuned for the correct harmonics of the L engine. The part was tested at Robello racing and verified with a stock damper to ensure the tuning was correct. The new part was then tested at Robello racing, real time functional tests on a dyno.

 

So that is my take, I really got to a point with this stuff and vendors that if they gave me guff, and the standard yea we can do that fast talking routine, I told them thank you, you don't have the parts and equipment I require for my car.  At the time ATI treated me like a bastard child because I was not building a small block chevy. So with about 90K invested in my car, I wasn't about to get into the standard engineering pissing match with them. BHK , robello, and myself developed a number of damper configurations and I am very happy with their product.

 

Now, if you really want the very best damper for your engine, you need a fluid damper, hands down that is the very best solution for the L engine damper, but again, they had not time for me to develop a damper for the L engine. However, they do make a damper, that shewbeck utilized with a few thousands honing would fit the L engine, but the pully issue was and still is a part that has to be custom made.

 

I think ATI is alot of hype, and their product in reality is not suited for the L engine as an off the shelf bolt on component.

[Tony D]

It's not "invested", it's "spent"...

 

A car is a hole in the air, suspended there by four rubber doughnuts which you can not eat.

Into this hole, you throw money, which you will never see again.

[ablesnead]

This is a continuation question that arise from the responses about dampners , I am fairly weak  in the theory here , but I have read that the counter weights on a crank

are weighted to balance the  offset rod (  and all attached parts ) , to eliminate a harmonic vibration,,,the so called bob weight....so if properly balanced , why would a harmonic balancer be needed ?  This question arose because some long established Z performance shop  sells a light weight ( aluminum front pulley ), in place of a balancer . any thoughts ?

[Tony D]

The aluminum pulley does nothing for dampening vibration, ask the BMW 6-Cylinder Guys chucking lightweight pulleys through their hoods about lightweight crank pulleys...

 

ATI or BHJ...

[johnc]

They don['t sell a pulley to replace the balancer.  The aluminum pulley bolts on to the front of the balancer.  At least the ones I've seen.  If someone is completely replacing the balancer with an aluminum pulley, then to paraphrase Tony D above - "They be idiots!"

[ablesnead]

Nope , bolt on aluminum crank pulley    199.00   Top End Performance..been using them for years  yada yada yada They say )

[NewZed]

Found on Google.  For discussion, don't know anything about its performance.

 

http://www.ebay.com/itm/Z-Car-Lightweight-Single-Groove-Aluminum-Crank-Pulley-/310246632272

 

and

 

http://www.racetep.com/nissan.html

 

 

 

I thought the damper was for harmonics damping, not balancing.  (Edit - semantics, maybe..)

 

Edit #2 - I can't find a sign on the interweb that anyone has ever actually bought and used one of TEP's damperless pulleys. 

Edited May 30, 2013 by NewZed

[ablesnead]

I'm wondering if this is similar to the belief that you need  some back pressure... I dont have the background to quote any science on the subject , but even on this forum 

members that pooh pooh harmonics , touting that the factory internals were so well balanced from the factory , only reply with the stock answer ..get a so and so  damper, seems to the uninitiated ( me ) like a little hypocracy . I am assuming that an out of balance reciprocating mass induces the harmonics that a damper is designed to damp....I am belaboring this point because it is a big red flag in the knife edge question of my original post....in Porsche boxer six'es we ran without dampers......hot rod VW's use aluminum pulleys across the board.... jut say'in

[NewZed]

The balance and harmonics concepts might be getting interchanged here.  Seems like everyone in this thread supports having a damper.  Where's the link to the thread about dampers where it's said you don't need one?  Only TEP and you seem to be saying that.