Jump to content
HybridZ

knife edge crank


ablesnead

Recommended Posts

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 ?

Link to comment
Share on other sites

  • Replies 46
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Posted Images

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.)

Link to comment
Share on other sites

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 by Tony D
Link to comment
Share on other sites

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.

 

gallery_95_475_34810.jpg

Link to comment
Share on other sites

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?

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

  • 1 month later...

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 ?

Link to comment
Share on other sites

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...

Link to comment
Share on other sites

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!"

Link to comment
Share on other sites

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 by NewZed
Link to comment
Share on other sites

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

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...