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RB26 vs RB30 crankshafts

khezz

By khezz,
in Engines & Forced Induction

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khezz Rising Star

khezz

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I am in the process of building an rb2630 combo. I keep getting conflicting reports about the strength of the rb30 crank. There's plenty of examples of rb26 cranks spinning past 9000rpm and making a 1000hp. I know the rb30 has a longer stroke but does it really effect the strength that much?

I have had two well known workshops tell me that you can't spin an rb30 crank to 9000rpm and it won't make 1000hp. 

Rips (love em) said, no worries. Machine, balance, grub screw and it will do it easy.

The block will use a prp  race/caps combo and an ATI balancer to help keep things in place.

What experience have people had with standard rb30 cranks?

Edited by khezz
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Duncan Grand Master

Duncan

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Are you aiming for a rev limit or power/torque output?

The key difference is not so much the longer stroke, but the taller block. This means rb30 block has a better rod/stroke ratio which is more efficient. RB26 block, particularly with a big stroke crank leads the piston to rock around in the cylinder way more.

Yes, longer stroke (which ever block) gives larger capacity but more piston speed for the same rpm which is theoretically a downside (nothing for free in physics) 

Having said that, I don't have a 1000hp RB30 or a 1000hp RB26.....neither of mine make more than about 600hp which is pretty tame these days. I would like both to last more than a few events though....

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Old man 32 GTR Proficient

Old man 32 GTR

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I’ve got a built 26/30 with a 68/70 turbo, last tune (with the new head setup) which is shimless set up, 1mm oversized valves cam tech 10.8mm lift cams, etc, was spinning to 8500rpm. Tuner said it would of revved higher but he capped it there to try to preserve it (somewhat). 
I’ve also heard conflicting information, some people say they are not safe past 7500rpm, others say they constantly rev to 8500+ with no issues. 
as for power, mine is making 580ish kw at the hubs, and there are plenty of examples of stock crank 30’s making 1000+ hp, but how long will it hold together? 
Ill let you know when mine lets go! Lol

khezz Rising Star

khezz

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Goal is to build a car that can be daily driven on 98ron fuel. Be able to run low 9s and go past 300kmh (once my balls grow big enough) at racewars on e85. For street I need responce/drivability. For drags I need outright power and for speed I need revs. Similar to what motive did with their r32 but better. Head will get the full treatment from Rams. Yes, I could go billet but I just can't see an extra $6000 value in 200cc capacity. I am not aiming for 1500hp+ either. 

Edited by khezz
Komdotkom Rising Star

Komdotkom

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Posted

It's about piston speed, your RB30 crank at 9k rpm has 17% more piston speed and load due to the increased stroke. Granted this is helped somewhat by a superior rod angle and ratio from the taller block, but you are still putting the additional load through a bearing with the same surface area.

Use RB30, more boost, less RPM

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khezz Rising Star

khezz

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I've been given some more insight as to why some people are hesitant. Aparently once you get to 8000rpm, the crank will start marking bearings. Some workshops try to get around that by increasing clearances or keep the revs to 7500ish.

I might have to just bite the bullet and go billet crank.

khezz Rising Star

khezz

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6 hours ago, Komdotkom said:

A billet crank won't make any difference unless you are going for larger journals and wider big ends to provide a greater surface area.

You could just buy a 2JZ....

Barra the world

BK Grand Master

BK

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On 23/09/2020 at 7:44 AM, Komdotkom said:

 

 

Back to the RB30 crank, some interesting comments from Lewis engines, make of it what you will:

"Every second phone call involves a discussion on RB pump failures. It is a dilemma that faces the unaware RB builder but can be addressed in several ways.

Basically the 6 cylinder inline engine is not a balance friendly item to deal with at high rpm. The crankshaft harmonics through the inline 6 crank are inevitable and increase in magnitude as crankshaft stroke increases.

This is no new engineering fact but has to be dealt with and manicured as per each individual combination and customers budget.

The Nissan RB engine will go 'past' or 'through' its harmonic periods very quickly and this will interprate the success or the destruction of most combinations. Some turbocharger combinations will find a huge ammount of rpm per time and these are the 'oil pump killers'. The cranks especially the long stroke RB30 will not be happy in these situations. We find in most race /high rpm engines to stick with a 25 or 26 stroke and when using the RB30 to be limited to max rpm of 7500rpm.

When using an RB30 a constant check of the balancer bolt tension is necessary.The first sign of crank harmonics and too much rpm for a combination, is the loosening of the harmonic balancer bolt in operation. The bolt must be done up to 400nm. This cannot be achieved unless the flywheel or crank is held with appropriate tools. A knocking type hammer or torque wrench and car in gear WILL NOT achieve sufficient tension."

Darren doesn't appear to be saying the crank won't do it (well implies it saying "won't be happy"), just more pointing out the extreme harmonics that are created and the effect of them when going past 7500rpm with a 30 crank. I know my Nitto 2.8 crank came with a balancing test report of being tested in 1000 rpm increments to 10000rpm, and would expect their 3.2 cranks to be at least tested to 9k rpm.

Ben C34 Grand Master

Ben C34

Posted
Posted
5 minutes ago, khezz said:

I wonder if the new oil drive systems or an external oil pump would help the issue. Great point that most people (me included) would have missed.

How is a different oil pump drive or external pump drive going to stop harmonics?

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khezz Rising Star

khezz

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12 hours ago, Ben C34 said:

How is a different oil pump drive or external pump drive going to stop harmonics?

It won't. But the previous post seems to suggest that oil pumps get damaged because of harmonics before bearings. If oil pump stops pumping, so does the rest of the motor soon after.

BK Grand Master

BK

Posted
Posted
14 hours ago, Old man 32 GTR said:

Nitto rate the 3.2 to 10000rpm

Yeah I know Nitto "rate" the 3.2 to 10000rpm and they "rate" the 2.8 to 11000rpm. As my 2.8 crank came from them with test results balanced up to a confirmed 10000rpm, I bet the 3.2 is only "tested" before delivery to 9000rpm to be safe, knowing realistically no one is spinning a 3.2 past 9k and a 2.8 past 10k.

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