What are the benefits of knife edging the crank? Are there any drawbacks?

 

May reduce "air drag" and reduces oil foaming- drawbacks include $$$ and hazard to hands if sharp enough LOL

 

i rather a person get a lighten flywheel its the same thing yet it is cheaper. knife edging the crank makes you rev quicker and able to move through oil quicker.

 

NO!!! the purpose mainly of knife-edging the crank is the let it slide through the oil better (pushrod engines). But, Honda cranks don't go through the oil. And do you really want to risk having an unbalanced crank?

 

Honda cranks don't go through oil huh? Are you sure? I'm pretty sure the lower 40% of the crank sits in oil.

Either way, I still wouldn't do it.

-Steve

 

Thats possible while the engine isnt running, but once you start it most of the oil is pumping through the block and head anyhow.

 

if the crank was spinning in the oil it would create lots of foam which would lead to lost oil pressure.

 

I believe it depends on what type of racing you're into. If you're just building your car as a daily driver/weekend racer, there's no point in knife edging your crank. You're better off with a lightened flywheel instead (and possible crank pulley).

 

i love all this contradicting information.......

 

It'll depend on what kind of racing you'll be doing. It'll be great (but maybe not worth the money) for drag racing, less rotating mass, but not so great for great for road racing where durability matters most.

 

is it good for every day driving and stop light to stop light drag racing and maybe autocrossing?

 

last on the list of things to waste money on- you probably need a dyno to see the difference.

 

No.

It's good when you need that extra .1 sec off your timeslip.

Otherwise a waste of $$. Just have the crank balanced.

 

Oh well............I guess it's official that I am lame. I sent it off to the machine shop, I will keep you all posted. All I can say is my set-up for 2002 is going to be crazy

 

$250 which includes polishing and balancing

 

You know what I think "knife edging" the crank is in a recent issue of SCC. I'll check it out and see if I can find a specific issue and page number.

 

as was told to me.... it doesnt gain power it just revs faster
hmm maybe a dyno could be able to show it revving faster .... hmm

 

hopefully that is the first time that you have ever said that, or it has crossed your mind -=Z

 

So, IM ALL SHO, why don't you teach us why you think it's important to knife edge the crank......

 

I have a knife-edged crank in my race-built B18C (track car). There are two reasons to knife-edge your crank.

1. Reduce rotating mass. Much like a lightened flywheel, "knife-edging" your crank involves removing material from the counter-balances (wing-like flanges) and therefore reduces rotating mass. This has the effect of "freeing" up horsepower since there's less parasitic loss of power involved in spinning a lighter (and balanced) crankshaft. This is the main benefit of "knife-edging" your crankshaft.

2. Reduces drag as the crankshaft cuts through the oil in the oilpan. Yes, Honda crankshafts do go through some oil in the pan, so having your crank knife-edged will reduce drag during this process. Again, this has the net effect of reducing parasitic losses, though in a different way than reducing rotating mass. Check out http://www.howstuffworks.com/engine2.htm for a animated diagram with the crankshaft in action.

In combination with a lightened flywheel, having a knife-edged (which should include lightening and balancing) crankshaft will help you move through the rpm range more quickly, help you keep the revs up when shifting gears, and will "free" up horsepower by reducing parasitic loss. In other words, you're reducing your drivetrain loss of power (which is about 14%, thus the difference between crank horsepower and wheel horsepower). You'll be lowering this say 14% drivetrain loss to say 12%. These numbers are just generalizations, not necessarily accurate in the case of my B18C engine, I'm just using them here for illustration purposes.


[Modified by Maxi, 2:16 PM 1/16/2002]

 

[Modified by IM ALL SHO, 10:58 PM 1/16/2002]

 

I wouldn't knife edge your crank. You can possibly weaken it and your crank really doesnt go through that much oil..... *cough* windage tray *cough*

 

Exactly.

Balancing it is good, but taking material off the crank is bad unless you REALLY REALLY need that extra .1 seconds

ALL SHO, I still don't understand what you mean....

 

I still haven't got the crank back yet, but I did take a test drive in crvtec 99 hatch today. This guy is using a UR flywheel and knife edged crank. The biggest thing I noticed is how insanely fast the car reached redline. It went from 2k to 9k in what seemed like an instant. When evrything gets dropped in I will post my dyno figures

 

ill explain my first reply to you... you said its only worth it if you need that extra .1 seconds off your timeslip... then i said i hope thats the first and only time you said that because... if you said it on 3 other occasions you would have already lost .4 seconds off a time slip .... .1 here .1 there adds up ..
thats what i was trying to say