Knife edged crank

Whjaxn17 · 04-22-2019, 04:27 PM

I've seen this mentioned in a thread or 2 on here as well as a few other forums online. Can someone shed some light on this as to what benefits could be expected from doing so?

Obviously less mass in the rotating assembly is good, but how much can be expected? The stock crank is right around 65-70lbs. What would be a realistic expectation in terms of a "goal weight"? 60lbs? 50lbs?

I've seen the same warning that it could cause street drivability issues, similar to a lightweight flywheel, but as of right now, I'm just trying to figure what the pros and cons really are to be able to compare them. Has anyone done this? This platform or not, just looking for some real world experience.

BGTV8 · 04-22-2019, 04:52 PM

Primarily for a race motor that spends a lot of time at peak revs .. reduces HP losses from windage in the sump. Doing this for a DD or non-competition motor will provide bragging rights only

Rusty · 04-22-2019, 10:12 PM

Quote:

Originally Posted by BGTV8

Primarily for a race motor that spends a lot of time at peak revs .. reduces HP losses from windage in the sump. Doing this for a DD or non-competition motor will provide bragging rights only

Plus you don't want to do it to a stock crank. A billet crank is better.

Spooler · 04-23-2019, 12:02 AM

They use to do it for 280z L28 engines when they stroked them. They would use a Datsun crank out of a diesel Maxima and pair them with 240z rods with customer pistons. The only problem is in a boosted application they would bend.

Whjaxn17 · 04-23-2019, 09:17 AM

Ok, no real benefit in a street car. Got it. I was only thinking of having it done while having an engine apart to have it built and wondered if it would be worth it. Boost was obviously the reason for having it built, though, which runs me into the problem Spooler mentioned.

So, I guess long story short, scrap the idea of using a stock crank. I just knew I had seen people say they were good for 900-1000hp, so I thought even after that, 600-700 would still be safe.

What about a billet crank? Would it be capable of holding the power minus the extra material? How do they compare in terms of weight? Edit: read somewhere else they're typically heavier than OEM due to being more dense

I'm aware this alone is a very expensive piece, something like $5k, but I'm just trying to learn about all this as I've never seen it discussed in depth.

This is strictly a street car for now, but I would eventually like to run the car in some half mile events such as TX2K or WannaGoFast once there is some more power in it.

bullitt5897 · 04-24-2019, 11:23 AM

Quote:

Originally Posted by Whjaxn17

Ok, no real benefit in a street car. Got it. I was only thinking of having it done while having an engine apart to have it built and wondered if it would be worth it. Boost was obviously the reason for having it built, though, which runs me into the problem Spooler mentioned.

So, I guess long story short, scrap the idea of using a stock crank. I just knew I had seen people say they were good for 900-1000hp, so I thought even after that, 600-700 would still be safe.

What about a billet crank? Would it be capable of holding the power minus the extra material? How do they compare in terms of weight? Edit: read somewhere else they're typically heavier than OEM due to being more dense

I'm aware this alone is a very expensive piece, something like $5k, but I'm just trying to learn about all this as I've never seen it discussed in depth.

This is strictly a street car for now, but I would eventually like to run the car in some half mile events such as TX2K or WannaGoFast once there is some more power in it.

Bryant Racing is the only Crank manufacturer I would run if your going aftermarket and knife edge. but as you stated $5k and a decent wait time. 18+ weeks when I last talked to them. Cranks are built to order and spec.

Now there is also BC and Marine Cranks you can run. BC is off the shelf and Marine is also built to order.

Whjaxn17 · 04-24-2019, 11:41 AM

Quote:

Originally Posted by bullitt5897

Bryant Racing is the only Crank manufacturer I would run if your going aftermarket and knife edge. but as you stated $5k and a decent wait time. 18+ weeks when I last talked to them. Cranks are built to order and spec.

Now there is also BC and Marine Cranks you can run. BC is off the shelf and Marine is also built to order.

Thank you for the recommendations. Would you care to take a guess as to the weight that could be expected?

SG4247 · 04-24-2019, 07:23 PM

Living on the “Knife” Edge – performancedevelopments.com

Spooler · 04-24-2019, 07:59 PM

Quote:

Originally Posted by bullitt5897

Bryant Racing is the only Crank manufacturer I would run if your going aftermarket and knife edge. but as you stated $5k and a decent wait time. 18+ weeks when I last talked to them. Cranks are built to order and spec.

Now there is also BC and Marine Cranks you can run. BC is off the shelf and Marine is also built to order.

He will spend just as much money at the machine shop to get that BC crank right compared to the cost of a Bryant crank. The quality is just not there.

SouthArk370Z · 04-24-2019, 08:19 PM

As far as I can tell, there's only two reasons to run a knife-edged crank: competition use where the very small HP gain could make a difference and because racecar. YMMV

Rusty · 04-24-2019, 08:36 PM

Quote:

Originally Posted by SouthArk370Z

As far as I can tell, there's only two reasons to run a knife-edged crank: competition use where the very small HP gain could make a difference and because racecar. YMMV

Rusty · 04-24-2019, 08:46 PM

Quote:

Originally Posted by SG4247

Living on the “Knife” Edge – performancedevelopments.com

I've broken a 1970 350 350HP LT1 forged crank.

SG4247 · 04-24-2019, 08:48 PM

We dont knife edge cranks in drag racing any longer..

Used to do that to stock cranks back in the day, when good parts were not available.

Heck we used to groove crank main journals too!

We are much smarter now, and recognize that balance, harmonics and durability are more important.

Whjaxn17 · 04-25-2019, 11:16 AM

Quote:

Originally Posted by SG4247

Living on the “Knife” Edge – performancedevelopments.com

This was an interesting and informative read.

I guess this is basically old technology/methodology that is best left in the past, then. Thank you for the input and information.

Like I said, I just wanted a little more in depth understanding of what the pros and cons would be, but it seems the potential problems far outweigh any benefits to be had.

1slow370 · 04-28-2019, 02:39 PM

Marine makes some incredible cranks for these motors. Cough*GTM'scranks*EndCough

04-22-2019, 04:27 PM	#1 (permalink)
Whjaxn17 Enthusiast Member Join Date: Sep 2015 Location: Alabama Age: 29 Posts: 420 Drives: 17 370Z 6MT Rep Power: 3365	Knife edged crank I've seen this mentioned in a thread or 2 on here as well as a few other forums online. Can someone shed some light on this as to what benefits could be expected from doing so? Obviously less mass in the rotating assembly is good, but how much can be expected? The stock crank is right around 65-70lbs. What would be a realistic expectation in terms of a "goal weight"? 60lbs? 50lbs? I've seen the same warning that it could cause street drivability issues, similar to a lightweight flywheel, but as of right now, I'm just trying to figure what the pros and cons really are to be able to compare them. Has anyone done this? This platform or not, just looking for some real world experience. __________________ 377whp/299wtq NA 704whp/519wtq, SOHO stage 2.5 IG: pearlywhite.z

04-22-2019, 04:52 PM	#2 (permalink)
BGTV8 A True Z Fanatic Join Date: Dec 2009 Location: 03350 Australia Posts: 1,514 Drives: 09 Nissan 370Z M6 Rep Power: 39974	Primarily for a race motor that spends a lot of time at peak revs .. reduces HP losses from windage in the sump. Doing this for a DD or non-competition motor will provide bragging rights only SouthArk370Z, Rusty, Spooler and 3 others like this.

04-23-2019, 12:02 AM	#4 (permalink)
Spooler A True Z Fanatic Join Date: Jun 2014 Location: Ga Posts: 13,852 Drives: 2013 Nismo 370z Rep Power: 2684392	They use to do it for 280z L28 engines when they stroked them. They would use a Datsun crank out of a diesel Maxima and pair them with 240z rods with customer pistons. The only problem is in a boosted application they would bend. Whjaxn17 likes this.

04-23-2019, 09:17 AM	#5 (permalink)
Whjaxn17 Enthusiast Member Join Date: Sep 2015 Location: Alabama Age: 29 Posts: 420 Drives: 17 370Z 6MT Rep Power: 3365	Ok, no real benefit in a street car. Got it. I was only thinking of having it done while having an engine apart to have it built and wondered if it would be worth it. Boost was obviously the reason for having it built, though, which runs me into the problem Spooler mentioned. So, I guess long story short, scrap the idea of using a stock crank. I just knew I had seen people say they were good for 900-1000hp, so I thought even after that, 600-700 would still be safe. What about a billet crank? Would it be capable of holding the power minus the extra material? How do they compare in terms of weight? Edit: read somewhere else they're typically heavier than OEM due to being more dense I'm aware this alone is a very expensive piece, something like $5k, but I'm just trying to learn about all this as I've never seen it discussed in depth. This is strictly a street car for now, but I would eventually like to run the car in some half mile events such as TX2K or WannaGoFast once there is some more power in it. __________________ 377whp/299wtq NA 704whp/519wtq, SOHO stage 2.5 IG: pearlywhite.z Last edited by Whjaxn17; 04-23-2019 at 10:33 AM.

04-24-2019, 07:23 PM	#8 (permalink)
SG4247 Track Member Join Date: Oct 2016 Location: OKC Posts: 790 Drives: 2010 touring Rep Power: 7842	Living on the “Knife” Edge – performancedevelopments.com Whjaxn17 likes this.

04-24-2019, 08:19 PM	#10 (permalink)
SouthArk370Z Premium Member Join Date: Nov 2010 Location: South Arkansas Posts: 8,435 Drives: 2014 Challenger Rep Power: 324198	As far as I can tell, there's only two reasons to run a knife-edged crank: competition use where the *very* small HP gain could make a difference and because racecar. YMMV __________________ Steering Lock Links - Search The370Z Bookmarklet - FSM @ NICOclub Mankind has progressed past the need for war but we haven't evolved that far. - NachoMahma

04-24-2019, 08:48 PM	#13 (permalink)
SG4247 Track Member Join Date: Oct 2016 Location: OKC Posts: 790 Drives: 2010 touring Rep Power: 7842	We dont knife edge cranks in drag racing any longer.. Used to do that to stock cranks back in the day, when good parts were not available. Heck we used to groove crank main journals too! We are much smarter now, and recognize that balance, harmonics and durability are more important. Rusty, wideglideleon, Whjaxn17 and 1 others like this.

04-28-2019, 02:39 PM	#15 (permalink)
1slow370 A True Z Fanatic Join Date: Aug 2009 Location: In the D Posts: 3,732 Drives: v8 74 260z ;) Rep Power: 7251	Marine makes some incredible cranks for these motors. CoughGTM'scranksEndCough Jayhovah likes this. __________________ ANSWER PRICE LIST Answers - - - - - - - - - - - - - - - - $0.75 Answers (requiring thought) - - - - $1.25 Answers (correct) - - - - - - - - - - $12.50

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