Crank lightening, not knife edging
 

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discuss.

I did it. Took off 7lbs. I thought it was really cool. Looked really cool. Just found out its 1 more thing that slows your turbo from spooling :(

I know I am next !

Did you gain low end tq by lighten the crank?

This isn't as expensive as knife edgeing is it? I'd like to get it done if it doesn't cost $600

Looks cool to me. I'm not sure why it'd slow spool, other than the engine reving quicker than the turbo can keep up.

it's like lighten flywheel that make the car rev up faster..

Unless there is a see side by side dyno comparison sheets, it seems a waste of money.

idk, i would think any weight removed that would rob power from accel/decel the rotateing assy up to speed would then be able to be trasfered to the wheels instead... now $ per power gained... thats another story

What all did you do to lighten it? I see the holes going towards the center of the connecting rod races, that's not stock, is it? Were the counter weights modified at all?

Is the lightest flywheel in the market not light enough?

I recently got a quote from Robello Racing to knife edge the crank, it was around $300.00. He thought that since I was drag racing it was not really a good idea. He recommended I do mild crank lightening instead.

Is that from jackstranmissions.com?

It works pretty well in some apps. From what I can see the counter weights are for rotational weight and driveability rather than engine longevity. It might loose spool, but it will also free up some power in the first few gears where the RPMs change quickly in any sort of meaningful acceleration.

$300 is a good price for a knife edge. I called a place about it and it was gonna run me around $900.

I do not know to what extent they would be doing on the knife edge for that $300.00 price, but Robello is a very reputable engine builder.

Rebello in Northern CA?

Mine was lightend(not knife edged), worked well till the OP exploded making it a boat anchor.

Someone told me never to knife edge a crank. Can't remember why or who told me that though. Anyways, lightening might be good to relieve some stress off of internal pieces too.

Just get the cast SOHC protege crank, its like 10 or 11lbs lighter

Knifing the crank without balancing the entire rotating assembly can cause excessive vibration at high rpm. If you want to remove any weight from the crank you might as well send it to an engine builder for balancing.

beat me to it... they work fine for n/a applications and low boost. plenty strong enough.

sohc 1.8, 91.5-94 (don't want a small nose...)

I just don't see it doing much. Enough to notice anyway. I'm with Jason on the flywheel comment.

Even N/A I think I would greatly prefer our forged and nitrided crank.

I've been running the SOHC crank for three years now, had it balanced along with the rods, sees 8k RPM's on occasion, its super smooth. Half the counterweights make for less windage loss as well.

Like other state, the more you leave the stock engine the better which they got their own magic.

Although many of you do not listen to this...

It is the same blcok of a competition Mazda 323 GTR pushing more than 300 HP, backj in PR who have done 10s the crank is stock...\\\\


IMO, leave it alone, the crank in stock trim is bullet proof.

Im next inline at Cardelli's for my 1.6 crank.

Are you doing this also Nick?

The loss in spool is due to some type of inertia situation I am not bright enough to explain. Mine had a shit ton taken off of it. 7 or lbs.

I saw no gains at all. It just looked cool and sounded smart. if budget is a worry, I would pass..

Loss in spool is kind of a myth.
The car may show less boost at a given RPM in logs in say 1st, but car accelerates faster.

No, my motor has been together for about 6 months or so.

Yes, out of CA. And I see I had the incorrect spelling. It is indeed Rebello. My bad.

It's a shame boost vs. RPM is so easy to log, since it's really not a good way of measuring anything. What you need to log is torque vs. time or RPM vs time.

Bingo. Load a dyno as if a Miata weighs 3500LBs and a 35R will spool like 2860 in terms of RPM.


The lighter crank means you are probbably spending less time in 1st, 2nd , etc gear, which will slow your spool a bit. Basically you have less time at a decent load state to spool the turbo. So chances are the perceived boost threshold will be higher, despite the car accelerating better.

From what I can see the weights are for driveability and NVH reduction more than for the engine itself, like the balance shafts you see in a lot of I-4s.

Rebello has been doing Datsun work for many many years and is one of the Bay Area's and maybe one of the nation's best 4/6 cyl machinists/engine builders.

They built a wicked n/a 2.4i setup for my friends 510 datsun that screamed.