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Power limits of RB25det bot end

Shibby

By Shibby,
in Engines & Forced Induction

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matlowth Proficient

matlowth

Posted
Posted

I know of a GTR making near on 400rwkw on stock rods (racepace dyno) which have been running in that tune for quite a while. It should be running @ Calder tonight. Not sure whether that car is just a freak, but it gets track raced very frequently, although I think that's running less boost at the track.

Emre & PH1's GTR's both make over 340rwkw and have been running around for over a year without any probs...

In any case, I haven't heard of anyone bending a rod on a GTR motor.

Cheers,

matt

so geoff how much rwkw power u recon u can get with your gtr rods before they start to bend?
rob77 Veteran

rob77

Posted
Posted

My engine died at somewhere between 340-380hp. I'm not sure as it wasnt dyno'd fully before the compression went on cyclinder 6 and 3 when the ringlands failed. Boost was around the 1.1-1.2bar (probably spiked to 1.3bar early on in the rpm limit and then settled down to 1.1-1.2) Pulling apart the engine we found that all the engine components were in excellent condition it was just a couple of weak ringlands that spoilt the fun. Just goes to show that you should always service the engine with good quality synthetic oil and regularly :P

FLYGTR Contributor

FLYGTR

Posted
Posted
!

 

I've just got shot peened, nitried rods...  They are series 3 VL rods though - apparently they were slightly thicker at the big end than the series 2....  Doubt that's gonna make it much stronger though...

 

 

matt

matt , while i dont doubt your expertise i didnt know there was a series three VL rod . Ive had a 11 sec vl a few years ago ( its now in the 10s ) and it used the std rod ( still does) with no dramas , it was just a 87 mdl turbo . In all the years of being in the VL scene ( ive moved on ) i never noticed a difference between rod thinkness and rods where never an issue at the time .

adam.

Actually RS500 would also have a fair amount experiance with vl rods as we had our cars at the same time.

GTRgeoff Grand Master

GTRgeoff

Posted
Posted

Ring lands are a real problem in 25t's stock, but like everyone else I was chasing too much power on a stock setup and intercooler.

I have to say the engine is a smooth as silk now and has great power on stock boost with the new Hybrid 800hp FMIC. I put the temp probe back in after the cooler and it was static 34 deg then during a couple of power runs Dropped to 28... the ambient temp with no water spray on the cooler. I am really impressed.

Has anyone got any thoughts on the crank limit of the RB25, as well as the head for max rpm?

Sydneykid Grand Master

Sydneykid

Posted
Posted

Hi Geoff, I have yet to find an rpm limit for an RB crank, if the balance is good.

I am not sure what you mean by the rpm limit of the head.

Is that the lifters? Cause 8,500 rpm seems to be a workable limit.

Is that valve springs? We change to Isky's when we go solid lifters so I guess 8,500 rpm is all I can say.

Is that cams? Standard cams seem to be OK to around 8,000 rpm, but power does start to drop off at 7,000 rpm unless you run a lot of boost. I haven't found the limit of after market cams, HKS have used 11,000 rpm.

Is that the ports? Cause there is no difference between and RB25 head casting and an RB26 head casting in that area. So it purely depends on boost and air flow, but 12,000 rpm looks OK on our flow bench.

Ditto valves, you can go 1 mm larger but that is way over 1,000 bhp stuff,

Does that answer your question?

GTRgeoff Grand Master

GTRgeoff

Posted
Posted

SK, once again, just gold. I have to admit I am looking to have a few rpm up the sleeve since changing ratios is a bit of a drama. Just to add to track flexibility, but without knowing any better I would be foolish to overdo it.

I was well known for valve bouncing the good old 18RG in the toyota rally car, fortunately without catastrophe. I'd call 8500 sufficient. Damn this thing is smooth now. Might have to plagarise smoothline's quote.

Do the 25's have a problem with 'pumping up' the lash adjusters/lifters like the scoobs with more power and rpm? Stated that the valves were failing to close fully by a poofteenth. It was considered mandatory to go to solid lifters a'la RB26 if pushing over some magical power figure. Obviously not since you consider the standard items good for 8500.

Sydneykid Grand Master

Sydneykid

Posted
Posted

Hi Geoff, if you run too much boost, the standard valve springs aren't strong enough to close the inlet valves. That is more of a limit than pure rpm. The hydraulics will pump up, it get worse with age, regualr use of 8,250 seems to be no problem though.

GTRgeoff Grand Master

GTRgeoff

Posted
Posted

SK, thanks. I may start to tweak the rpm limit when I go for tuning.

Steve-SST, how long did it run at that rpm limit and when you say he drove it fairly hard, including track effort?

Roy, I was an AutoCad guy, but now have Solidworks 3D design tool and Cosmosworks for the FEA and am sold completely. $30K for the lot with a good notebook to run it all. Gives a full 3D rendered avi of the deformation. Solid, shells, thinwalled members, heat, animation of multiple objects with constraints, interference, design optimization. Just no computational fluid dynamics. Would have been handy when I had to wind tunnel test an armoured vehicle which cost 200K. Coulda CFD'd instead.

matlowth Proficient

matlowth

Posted
Posted

Hrmmm - that was just what my mechanic called it... Dunno the specifics on it, but I know it was "slightly" thicker than the normal ones...

My mechanic said he'd never come across them before...

If I remember correctly, I think the Nizpro guys said the limit for stock rods is around 500-550 ft/lbs of torque... Run less than that, and they're fairly reliable, much more than that, and the chance of bending a rod goes up exponentially.

Cheers,

matt

matt , while i dont doubt your expertise i didnt know there was a series three VL rod . Ive had a 11 sec vl a few years ago ( its now in the 10s ) and it used the std rod ( still does) with no dramas , it was just a 87 mdl turbo . In all the years of being in the VL scene ( ive moved on ) i never noticed a difference between rod thinkness and rods where never an issue at the time .

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