Safe Rev Limit For Built Rb25

[Rolls]

Just wondering what you guys think is a safe rev limit for my motor, the tuner set it at 7500rpm but I want to make sure it is likely to last hitting these revs.

it has been build with acl race bearings, stock rods, arp rod bolts, arias forged pistons and everything else has just been freshened up and is standard. Running 18psi which drops down to 15 at the top end on a gcg highflowed rb20 turbo making 236kw and dropping off after about 7300rpm

Would you guys set it lower at say 7-7.3k? or you think with decent bearings and better rod bolts it should be fine hitting 7500?

It is a street car and only occasionally tracked, if I do I will aim to keep revs below 6500-7000 just to be kind to the motor.

[The Dan]

Just wondering what you guys think is a safe rev limit for my motor, the tuner set it at 7500rpm but I want to make sure it is likely to last hitting these revs.

it has been build with acl race bearings, stock rods, arp rod bolts, arias forged pistons and everything else has just been freshened up and is standard. Running 18psi which drops down to 15 at the top end on a gcg highflowed rb20 turbo making 236kw and dropping off after about 7300rpm

Would you guys set it lower at say 7-7.3k? or you think with decent bearings and better rod bolts it should be fine hitting 7500?

It is a street car and only occasionally tracked, if I do I will aim to keep revs below 6500-7000 just to be kind to the motor.

The factory redline is 7500 isn't it?

Plus the turbo wouldn't make more power past 7000rpm I would imagine so there is really no sense shifting after that point

[Lithium]

Doesn't sound like there is much point revving it past 7000rpm anyway.... crank collar and oil mods been done to it?

[Rolls]

Doesn't sound like there is much point revving it past 7000rpm anyway.... crank collar and oil mods been done to it?

Not that I know of, would have to speak to the builder. I try and shift around 7000rpm but with the crap tyres I have it hits the limiter half the time as it doesn't get traction.

Makes peak power from 6300 - 7200rpm basically flat there at 236kw

Edited September 17, 2010 by Rolls

[R31Nismoid]

Ask whoever built it - they would be in the best position to make that call

[s13-steve]

i think 7200 rpm would be ideal

[KiwiRS4T]

Stock will run all day at 7000. Is it fully balanced? If you want to change at 7K then 7200 sounds like it would do.

[Dose Pipe Sutututu]

I had my stock motor set at 7500rpm when I had the PowerFC in it, I just shaved off 4 degrees of timing rows 18, 19, 20

[Rolls]

Stock will run all day at 7000. Is it fully balanced? If you want to change at 7K then 7200 sounds like it would do.

Yep that was part of the assembly everything was properly balanced and all tolerances double checked.

Whilst I don't have any need to rev it over 7000 I guess I am more curious about the mechanical strength. I'm sure someone has done the calcs of where bits tend to let go and which parts need to be strengthened to overcome this.

[The Dan]

Yep that was part of the assembly everything was properly balanced and all tolerances double checked.

Whilst I don't have any need to rev it over 7000 I guess I am more curious about the mechanical strength. I'm sure someone has done the calcs of where bits tend to let go and which parts need to be strengthened to overcome this.

We rev our race cars to 8500 and 8800rpm. I have friends who rev their RB26's to 10k and the Nitto R34 would have to rev somewhere close to 11 or 12.

Forged crank if you wanna go over 9000. Harmonic balancer upgrade, oil pump upgrade...etc....etc...where do you want to stop?

You should just tell us how far you want to rev your engine and we can tell you what you need to upgrade to safely do it

[rad100]

yeh im setting mine to 7200-7300 with a 3076r.

n1 pump, metal jacket balancer, jun collar, spool rods, pistons etc..

[NYTSKY]

^^^^ What Dan said.

I really really miss the sound of my 25 at 8000rpm

[andymoocow]

^^^^ What Dan said.

I really really miss the sound of my 25 at 8000rpm

I miss the sound of your engine too mate, what a cracker it was!

I have a fully rebuilt RB25, my tuner set the rev limit to 7200, only ever hit it at Texi days when its wheel spinning and boosting and then WHACK, limiter. Does not make any more power from roughly 6800 onwards, but it does sound hot

[Rolls]

Forged crank if you wanna go over 9000. Harmonic balancer upgrade, oil pump upgrade...etc....etc...where do you want to stop?

You should just tell us how far you want to rev your engine and we can tell you what you need to upgrade to safely do it

I don't really need to or want to rev it any higher due to the turbo setup, just trying to get an understanding of where it would fail and why with the current parts. A lot of anecdotal evidence with peoples personal rev limits but I haven't read much about where they will actually fail and what parts will go.

Also providing a perfect tune what actually does kill them, limiter bashing, outright power, or just spinning the rpm too high no matter what the load is?

Edited September 17, 2010 by Rolls

[FineLine]

I don't really need to or want to rev it any higher due to the turbo setup, just trying to get an understanding of where it would fail and why with the current parts. A lot of anecdotal evidence with peoples personal rev limits but I haven't read much about where they will actually fail and what parts will go.

Also providing a perfect tune what actually does kill them, limiter bashing, outright power, or just spinning the rpm too high no matter what the load is?

Revs is the biggest killer. As you increase revs the bearing load increases exponentially. I did see some figures somewhere but it escapes me atm, what they were claiming was that to go from 7500 to 8500 rpm actually doubles the load or something along those lines.

[R31Nismoid]

I think it was 500rpm wasnt it? Either was it's massive

And what actually lets go can vary as it depends on what parts are inside.

poor rod bolts would mean a rod lets go. if not it could be bearings. Its all subjective in many cases as to what the 'specific' weak point is.

Even if you address a specific weak point, nothing to say it wont fail from just simple bad luck - nothing is perfect.

[ARTZ]

I reckon it will be fine, not like your running heaps of power, So all though its revving hard theres not the strain that say 300kw would put on the enigne..

I wouldn't worry too much, just drive it and remember to shift before 7500 and it'll be fine.

Id say your tuner knew there was more power up top so gave you the ability to use it..

Sounds like you've built a nice revvy motor that will have very snappy acceleration, be great out of corners...

[paulr33]

i think you are best keeping it low as possible where it still makes good power and doesnt drop off

if the boost is already dropping off, thats a sign its becoming in-efficient already

ive had my 33 for about 7 years now on std turbo and engine still with 230k on the clock (got it at 53k)

and i never see the limiter and usually short change the gear around 6500rpm as you can feel the power trail off

so i think this is a good insurance policy as a general practice, it may even make the car overall quicker vs letting it rev out to 7500rpm

[ARTZ]

Not that I know of, would have to speak to the builder. I try and shift around 7000rpm but with the crap tyres I have it hits the limiter half the time as it doesn't get traction.

Makes peak power from 6300 - 7200rpm basically flat there at 236kw

Sounds like the perfect limit it, holds 236kw at 7200+ so if you want to hold it in gear for a long corner for any reason you can without hitting the limiter...

hitting the limiter is nasty but holding it right near it is great and thats where all the power is..

If a 300kw car can hold 7000 no worries i reckon a 236kw one, handbuilt with good bearings will have no problems at all at 7500 as long as it was built properly..oil cooler would be advisable if your up there all the time though..

Edited September 17, 2010 by Arthur T3

[jarrod83]

i could be wrong but i remember reading in one of the magazine that that if you double the rpms you increase the load by 10 fold..

off the top of my head if you were spinning twice as quick, your pistons would be moving twice as fast, 4 times the energy with half as long to slow down, so thats probably 8 fold right there.. so from 7-8, thats roughly 50% increased load on the pistons n bearings.. but at 7300 thats only roughly 15% more.. if you take into consideration your forged pistons are probably slightly lighter than stock pistons, along with stronger bearings.. its probably a good compromise

Jarrod