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The jury is still out regarding whether I build a stock stroke RB25DET engine, or build an RB30 based unit for my track R33 GTS-t. I fancy a short stroke engine, the RB25 seems a lot smoother than even the RB26 DETT, and that appeals, I was wondering if anyone has built a seriously high RPM RB25DET engine? Maybe around 9000 RPM, built to last at those revs on the track? Is any commercially available stock stroke steel crank available for the RB25 engines? Thanks.

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The jury is still out regarding whether I build a stock stroke RB25DET engine, or build an RB30 based unit for my track R33 GTS-t. I fancy a short stroke engine, the RB25 seems a lot smoother than even the RB26 DETT, and that appeals, I was wondering if anyone has built a seriously high RPM RB25DET engine? Maybe around 9000 RPM, built to last at those revs on the track? Is any commercially available stock stroke steel crank available for the RB25 engines? Thanks.

Your kidding right, do you reallly believe that 1.35 mm extra crank throw would make an RB25 smoother than an RB26? The resulting 2.7 mm extra stroke is a non event in balancing terms. More likely is the individual tune of the engines you are comparing.

Moving on, 9,000 rpm is no problem for the standard crank. But the cylinder head ancilliaries are not as easy (read cheap) to upgrade to handle that sort of rpm as an RB26. Other than the crankshaft, everything that goes up & down or around & around needs to be upgraded. Sure you can do it, what is required is well known, the parts are available, no rocket science there. But why bother? When you can do an RB26 for less cost. Why bother when you can do an RB31DET for similar cost and it will make more power using 7,500 rpm than the RB25DET will using 9,000 rpm, Why bother, when in comparison, it will do very few K's between rebuilds.

My 20 cents worth:cheers:

Just my own feel for these engines suggest the RB26 is NOT as smooth as the RB25, dynamics wise. Same as the 2.5 Soarer engine is FAR smoother than the similar, but longer stroke 3 litre Supra TT engine, or even the N/A 3 litre 2JZ-GT units. Anyway, I take what you say about capacity = torque and lower stress, but I am from a race background and I just love the sound of a high revving straight six. For sure, a long stroke 3 litre will pull great torque figures, at low RPM, but there's more to building a special car / engine than practicalities, and I would consider additional cost and leser intervals between rebuilds maybe a worthwhile downside for the "excitement factor" of something that sounds more like a race engine than a diesel, no offence. I may well end up going the "diesel" route, but I feel I should explore bothe options fully before comitting. I just like short stroke engines.... :P

Sydney kid

At what rate does engine wear increase with RPM?

Wouldn't an RB30DET have a longer life between rebuilds than a high reving RB26DETT?

Or would it be neglible on a highly boosted motor anyway?

If ALL other things are equal, the higher the RPM, the higher the wear rate. It's not a straight line either eg; 8,000 rpm is NOT twice as stressful as 4,000 rpm, more like 20 times in my opinion. But I have no hard numbers on it, I can't say a 7,500 rpm RB30 will last "X" and a 9,000 rpm RB25 will last "Y". What I can say is a 7,000 rpm RB30 (standard internals 475 bhp) will last a long time, we service one that has done over 50,000 k's and 4 1/2 years and it gets USED.

The real issue here is cost, for the same power, it is a hell of a lot cheaper to build (and maintain) a 7,500 rpm 3.1 litre than it is to build and maintain a 9,000 rpm 2.5 litre. Of course the 3.1 litre will have better response and higher average power at lower rpm. If you look at using a 9,000 rpm 2.5 litre properly, you really need to considering gearing. The standard gearbox ratios are going to be too widely spaced, it will drop off the power band on upchanges if a close ratio gearbox isn't used. In addition some consideration may be necessary into using a lower final drive ratio (9,000 rpm is 20% higher than 7,500 rpm). This adds substantially to the cost.:P

Just my own feel for these engines suggest the RB26 is NOT as smooth as the RB25, dynamics wise. Same as the 2.5 Soarer engine is FAR smoother than the similar, but longer stroke 3 litre Supra TT engine, or even the N/A 3 litre 2JZ-GT units. Anyway, I take what you say about capacity = torque and lower stress, but I am from a race background and I just love the sound of a high revving straight six. For sure, a long stroke 3 litre will pull great torque figures, at low RPM, but there's more to building a special car / engine than practicalities, and I would consider additional cost and leser intervals between rebuilds maybe a worthwhile downside for the "excitement factor" of something that sounds more like a race engine than a diesel, no offence. I may well end up going the "diesel" route, but I feel I should explore bothe options fully before comitting. I just like short stroke engines.... :D

Hi Chris, I agree with you on the 1JZ versus 2JZ comparison, but there is a 14mm difference in their strokes. This is not a reasonable comparison with the 2.7 mm difference between an RB25 and an RB26. Having dissassembled quite a few, I can say that the RB26's seem to built by Nissan with much tighter tolerances than RB25's and the standard balancing is far superior. In my humble opinion, any smoothness advantage in an RB25 is purely their state of tune, nothing to do with their 2.7 mm shorter stroke.

At this point is is worth noting a couple of things. Firstly, there is plenty of evidence to suggest that a square engine (same bore and stroke) is the best compromise between rpm capability and torque development. Secondly, the RB30 has a demonstrably superior stroke/rod length ratio of 1.8 compared to the RB25's 1.6. So not only does the longer stroke give power benefits, the better stroke/rod length ratio accentuates this. As a bonus there is less side loading wear on the pistons, conrods, bores and bearings.

Similar to you, I have a liking for high rpm, the 18,000 rpm of an F1 engine is very pleasing to my ear. Have a read of my previous post and then tell me if the $10+K you spend on transmission and top end upgrades to make an 9,000 rpm RB25 effective and reliable wouldn't make an RB31 sound pretty nice. Hell, for the extra money I could get the RB31 to rev to 9,000 rpm and then you would have the best of both worlds.

There are many layers to this sort of discussion, the stroke comparison is really only scratching the surface.:P

i dont know about RB25 engines....but i have recently lightned/knife eged the crank on my rb26 and boy did this make a diffrence....while i had the engine apart i installed hks pistons,rods and metal head gasket.The engine now produces a huge wailing sound from about 4500 through to 9000 rpm and pull sooo much stronger between these figures,the revs build very quick aswell...might be worth you lookin into it

What is the piston speed of an RB25 at 9000rpm and an RB30 at 7500rpm? ETC ETC.

The piston speed of the RB30 piston at 7,500 rpm is slightly lower than the piston speed of the RB25 at 9,000 rpm (ie; 21.25 versus 21.30). :cheers:

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