Building A 25 To Spin To 9-10k

[Simon-S14]

hypothetical question here but whats involved in building a motor to spin to such RPM? Would be using a neo head for solid lifters but what about the bottom end?

and go....

[zebra]

throw it in the bin and use a 26,

Not saying it cant be done with a 25, but easier to do using a 26.

9000+ will need huge cams which the NEO head cant take

The bottom end will need to balanced to within an ich of its life, be light weight etc, can be done on stock crank but not sure I would do it

[Sheriff Wan]

For the price you would spend on building an engine like that you cant go past the 26 head.

Other than that you would need a very well put together bottom end and supporting mods i.e. oil supply etc.

[Roy]

Well, at those revs nothing in the std RB26 head is going to be all that flash either. So the NEO head is later model, from reports flows perfectly fine. Has variable timing on the inlet cam, something the RB26 does not have. And there are people that can adapt the inlet plenum to the Neo head.

So, I dont think its all that far fetched... i think the bigger issue is if you are spinning the thing that hard is you will have to look at the pulley sizes as your PS and water pumps will be going like crazy and that probably wont be great

[GTScotT]

I dare say that the reason the RB26 gear is interchangeable between RB25 heads is that there is stuff all between them. You can swap the cams, the springs, the shims, the buckets, the caps. I dont see why you couldnt do the same port work and mods to the NEO head as the RB26 and do the same revs.

From some reading, head wise you will be looking at port matching/springs/retainers at a minimum. Valve sizes could use some work, AFAIK the exhaust valves are a little small on the 25s. Im not sure what is done to the cranks to get them to rev, yet rods and slugs would be off the shelf items for this application. Lubrication mods would be a MAJOR point to cover.

You may want to look at well documented cars such as the Mines R34 for specs to see what they did to rev to 9. Remembering that the bottom end of the 25 is not far from the 26. This has been done to death Im sure, just the sort of information that those who know are never willing to give up .

GL, your cars a machine as it is.

[N1GTR]

What's required? Money.

My rb30 spins to that sort of number (well, a bit over tbh), there's really no need to spin that hard in 99% of situations you'll find yourself in.

Regardless of that, what I did to get it to spin that hard;

26 head

Tomei buckets

Tomei procams

Tomei springs

N1 R33 balancer

JUN oil pump

ACL bearings

Rods pistons etc

The rotating assembly was very carefully put together after being balanced with clutch.

Then there's oil/fluid mods....

[R31Nismoid]

10,000 or 9,000 Steve? Big big difference

Drawing on a big assumption here, given Simon is drifting etc, i would assume the intention is the motor will see a lot of time @ that given RPM rather than the odd flick

The crank will need some serious attention IMO, any lighter it can be made the better, lighter everything basically.

The head stuff is a given and pretty well documented. Tomei pump would have to be the choice as well if you stuck with that type of pump setup.

As an example there is sooooo much meat that can be taken off a RB30 crank.

Having seen a RB30 crank myself that went on a very serious diet for a certain car seeing very similar work to what Simon would be doing (assumption again), and it stood the extreme test for quite some time without issue.

This is long term, constant high RPM life, not the odd expedition into the upper RPM. Such work would see 5k burnt just there, so costs do add up rather quickly.

Could the same be said for something that didnt have such treatment? Who knows and its highly subjective like most things with limited volume examples.

[Simon-S14]

drift does see some large rpms sometimes... its always handy to have a few more rpm to extend the drift cause not every situation you are able to change up. changing the diff ratio doesnt always help either.

i am looking at building an engine as a spare over a period of time and im just looking at ideas to what i can do with it. sure i could just put forged pistons and rods in it and be done with it but would be nice to go a little bit wilder on the set up. i do realise that this = money as well.

as roy said i think one of the biggest issues is going to be the overspeeding of the ps pump, alt, water pump etc which should be easily reduced by a set of reduction pulleys.

[zebra]

Well, at those revs nothing in the std RB26 head is going to be all that flash either. So the NEO head is later model, from reports flows perfectly fine. Has variable timing on the inlet cam, something the RB26 does not have. And there are people that can adapt the inlet plenum to the Neo head.

So, I dont think its all that far fetched... i think the bigger issue is if you are spinning the thing that hard is you will have to look at the pulley sizes as your PS and water pumps will be going like crazy and that probably wont be great

I dare say that the reason the RB26 gear is interchangeable between RB25 heads is that there is stuff all between them. You can swap the cams, the springs, the shims, the buckets, the caps. I dont see why you couldnt do the same port work and mods to the NEO head as the RB26 and do the same revs.

From some reading, head wise you will be looking at port matching/springs/retainers at a minimum. Valve sizes could use some work, AFAIK the exhaust valves are a little small on the 25s. Im not sure what is done to the cranks to get them to rev, yet rods and slugs would be off the shelf items for this application. Lubrication mods would be a MAJOR point to cover.

You may want to look at well documented cars such as the Mines R34 for specs to see what they did to rev to 9. Remembering that the bottom end of the 25 is not far from the 26. This has been done to death Im sure, just the sort of information that those who know are never willing to give up .

GL, your cars a machine as it is.

The problem with the NEO head is that it cant take over 9.1ishmm lift, so while you may be able to take 10000rpm it would prob make 100 less horsepower than it would at 8000.

My rb25 saw 9000rpm once..it survived...but did it make any power...nope! probably made less than what it did at 3000

[FineLine]

Been there done it. Unless you're prepared to throw some serious coin at it forget it.

If i were to do it again It would be built around a counterweighted crank of some description.

And, as most have already said. it takes a very developed head to make it worthwhile. revving to those numbers without a head built to take advantage of it is a waste of time.

[STATUS]

yours is a neo so its not a real hard thing to do.

[lachlanw]

rips have had the 30 to over 11000 and it survived . think it gerularly sees over 9 . just need a big can of first class engineering .

[Simon-S14]

yours is a neo so its not a real hard thing to do.

my neo is currently limited to 7000... should i be reving it higher??

[R31Nismoid]

7500 is where i had my stock RB25 (not a neo, older etc) for a good 3 years before it failed, i would do that to a NEO no problem.

No more though without rod bolts being changed IMO.

A few dyno graphs of NEO's have them 7500rpm in the RB25 thread im fairly certain.

But then depends as you are giving it a lot of curry more-so than my daily driving would.

[Simon-S14]

yeah i found it strange that the factory revlimit for a neo on my ecu was 6900 seems aweful low heh

[R31Nismoid]

Ye it is a bit odd.

oh and my motor didnt fail because of 7500 (just thought id clarify)

was poor tune