Maximum HP @ RB26DETT stock crank?

[mull]

I've read on the great interweb that a company in Australia (or was it NZ?) had dynoed 1200 HP on a stock crankshaft.

 

Anyone know if this is true to start with?

 

How many ponies are you/or your friends running on stock crank?

[stony]

Mine dynoed at 600 at the wheels thru a powerglide so that is close to 750 at the crank. to make 1200 takes alot of money and im not sure why a person that has the money to make that kind of HP would not use a aftermarket crank for that application.....

[m4xwellmurd3r]

possibly because the stock crank is so good they don't see a need to replace it?

[Careless]

possibly because the stock crank is so good they don't see a need to replace it?

 

well if there's better, then why not go for better?

 

Lighter weight? stronger at the same time? I'm sure they exist.

[stony]

IF they actually used the stock crank... to get that kind of HP they had to be turning it to and ungodly high RPM. So when they say stock....I'm sure it is a highly modified / balanced "stock" crank

[cheftrd]

There's two ways to make "horsepower", torque and rpm.

 

Torque puts a mean twist (deflection) on the crankshaft. As an example, a top fuel dragster or funny car runs a super heavy-duty billet crank. I've read that crank deflection in these engines is upwards of 20*. That means the front-most cylinder is 20* ahead of the rear-most cylinder at full boogie. It's so severe that the cam is ground with front cylinder valve timing events equally advanced (or the rear retarded, whatever). Anyway, if you were making that kind of power with torque, meaning you're doing it with extreme cylinder pressure, crank deflection in the stock crank would be serious. Even if it's strong enough to transfer the power without breaking, there are serious power gains to be had if your valve timing events are all in sync with each piston, given their position. I'm going to take a shot in the dark and put a 100 hp per 1,000 hp number on it based loosely on the differences I've seen between stock and billet crank RB26's. In addition to deflection, there's wobble to deal with. Those kinds of forces can make the crank wobble on it's axis. Think of it as a little larger stroke as the rod pin is pushed out and down with each power pulse. In effect, the carnk would look like a wavy line. The more the crank wobbles on it's axis, the more the snout whips around, causing timing belt whip, throwing off valve timing events, ignition timing, creating very bad harmonics, etc. That wobbling also eats up bearing oil clearance, and consequently eats up bearings (and the engine when a main bearing spins in it's journal).

 

And then there's rpm. Making the power by spinning the engine faster, but not necessarily twisting the crank harder. Rotational forces increase at the square of the rpm. To turn the crank 10,000+ rpm it needs to be strong, well balanced, and straight. The stock crank is not fully counterweighted. It was never intended to turn that fast. Without those counterweights, it'll wobble when turned to those speeds, not from the power pulses as in the example above, but from extreme imbalance. Those pistons and rods weigh a ton or more at that kind of rpm. The result is the same.

 

So you have to ask yourself... Can the stock crank "handle" it? Maybe. But can anyone tell me that 100+hp and extending main bearing life by 10 times is not worth $2,500? That's on the conservative side. If the crank lets go at 10K rpm, there's a good chance that the entire engine will be a write off

[turbo_fb]

There is a gtr in Norway running 1k hp on stock crank.

He blew his engine last year though and today actually, he's on the

dyno with his new os/giken RB3.0 engine.

Maybe I can get a vid out this week.

[cheftrd]

There is a gtr in Norway running 1k hp on stock crank.

He blew his engine last year though and today actually, he's on the

dyno with his new os/giken RB3.0 engine.

Maybe I can get a vid out this week.

 

 

There's a few RB26's making 1,000hp with the stock crank.

[mull]

Good to know.

 

I'll be keeping on the safe side of 1000 hp anyway though : )

[stony]

Hey Mull i havent seen any video or pic updates of your car how's the project coming?

[RIPSNZ]

1000hp is no problem for a stock crank. When people say that a stock crank can't take that sort of power, I ask them to show me 1 case where a stock crank itself has failed, I am yet to hear of 1 case where the actual crank failed due to power/rpm. We run a street 240z at 1100hp+ and 8.7 on the 1/4 with a stock unmodified crank turning 9000rpm, stock cradle and stock used mains bolts just to prove they are perfectly capable of handling more power than most will ever make. A RB30 we have just dyno'd made just over 1300hp/2 bar/9000rpm and although it does have a billet crank by my customers insistance, if it were my own engine I would have been happy to stick with stock. We will be really leaning on the 240z stock crank motor and I am quietly confident we'll be into the 7s in street trim before we'll have any problems with it.

[mull]

Hey Mull i havent seen any video or pic updates of your car how's the project coming?

Not yet, no. But there will be sooner rather than later. Starting now anyway : )

 

RIPSNZ - thanks for a much needed reply : )

[cheftrd]

1000hp is no problem for a stock crank. When people say that a stock crank can't take that sort of power, I ask them to show me 1 case where a stock crank itself has failed, I am yet to hear of 1 case where the actual crank failed due to power/rpm. We run a street 240z at 1100hp+ and 8.7 on the 1/4 with a stock unmodified crank turning 9000rpm, stock cradle and stock used mains bolts just to prove they are perfectly capable of handling more power than most will ever make. A RB30 we have just dyno'd made just over 1300hp/2 bar/9000rpm and although it does have a billet crank by my customers insistance, if it were my own engine I would have been happy to stick with stock. We will be really leaning on the 240z stock crank motor and I am quietly confident we'll be into the 7s in street trim before we'll have any problems with it.

 

I've personally seen three failures, all three at the rear of the crank between the #6 rod pin and the last main pin, two of which destroyed a lot of the engine. All three were in GT-R's leaving the line at the clutch drop with ATTESA lock-out. Talking with friends over at HKS, they've failed a few during R&D. I've also seen the data sheets showing the difference in deflection and runout between stock and full-counter 4340. Not in a million years would I run a stocker in a 10,000 rpm $20,000 customer engne.

[RIPSNZ]

Interesting, and I suppose what you describle could happen although I havn't personally seen it.

 

We've run some pretty low times (8.7) on a stock crank without issue and have never heard of the type of failers you talk about.

 

Obviously most people wouldn't be leaving the line anywhere as hard as perhaps these cars were, any idea of the 60ft times and weight of these cars?

 

Will keep it in mnd,

 

Rob

[johnc]

The real question regarding how much horsepower a part can handle is: How long does the part last at x horsepower. I'm sure a stock RB26 crank can do one dyno pull at 1,500 horsepower. Can it do two?

[RIPSNZ]

I've been thinking about this some more.

 

The cranks described above didn't actually fail from the high rpm, or the power they were making at the time, ie, if they were on a dyno or in a different situation they wouldn't have failed.

 

They failed due to a very sudden shock loading applied to them in a way that is not always the case for alot of high output RB engines.

 

If they were in a 'locked' 4wd situation, with a very strong clutch and alot of traction, when they launched there would be tremendous loads on the rear of the crank, hence they broke there.

 

Obviously a good billet crank will cope with this situation better, no dought about that, but it still doesn't actually mean that under different circumstances, ie a launch without 50/50 lock up, a high speed road car, an auto drag car or other applications that the stock crank would have failed.

 

I agree, in the sitautaion described above a billet crank would be better, but I still maintain that a stock crank in other applications is still fine with 1000hp+ and 9,000rpm+ and is still reliable as we have it in our own car doing just that.

 

Rob

[Booztd 3]

Stock Block, tomei head gasket, head studs, stock head

 

Mileage unknown.....

 

 

Been running around on a daily driven tune making ~540-550rwhp and beating on it daily with no issues

[stony]

What PSI were you running there Andy??

[Careless]

I've been thinking about this some more.

 

 

 

Me too, and to bring something into consideration:

 

cheftrd, you mentioned in one post in another thread that the bump-sticks on top fuel dragsters have their timing phased out of sync with the other lobes on the same cam because of the torsional forces applied at WOT off the line, causing the cam to twist violently in a instant.

 

I think this is the same thing that's happening to the crank right when the clutch grabs hold...

 

cranks, having offset crank pins, would make it hard for torsional forces to travel down the entirety of the crank and flatten out along the axis which it spins. Since the 6/rear pin area is closest to the clutch and has no where to transfer the load from the immediate grabbing of the disc... twisty = snappy.

 

That sounds like a believable reason to me.

[stony]

causing the cam to twist violently in a instant.

 

 

 

 

You meant crank right?