Rb25 Head Questions

[stiddy]

hey all,

Building an RB25. Build is in the process, bottom end is done, time for the head. (stock with tomei poncams and cam gears)

Now talking about the head. What would be the better option and why? What should I be weary of? suggestions?

1. RB25 head, ported and polished with a solid lifter conversion. Decent cams.

2. RB25 neo head, ported and polished. Decent cams. (have been told by several people that these are the best heads of the 3)

3. RB26 head, ported and polished, again decent cams.

by saying decent cams, im undecided on what I want at the moment, but am after that nice big angry lumpy idle) Procams 270s or so. After the new head is done am planning to spin to 9000rpm.

About the car. CP forged 20thou over pistons, manley forged rods, machined balanced etc etc few other odds and ends such as mains girdle, jun oil pump, lewis sump, ross balancer etc etc... Custom exhaust manifold, BW 63mm turbo(am going bigger turbo if need be), plazmaman plenum and t/b. Trust cooler, 3.5in exhaust. Haltec platinum pro ecu, supporting fuel system, running E85. Power, maybe asking alot BUT I want 650/700rwhp. originally made 510rwhp at 1.7bar. Love to see 2bar and 700hp. Its all still a work in progress.

Help and suggestions greatly appreciated.

Thanks in advance,

Matt

[FineLine]

I'm using the 25 head with a supertech solid lifter conversion simply because I already had the complete hot and cold side ready to bolt on. If I were starting from scratch I would probably use a 26 head Just to save on the cost of the conversion but given the hassle of getting rid of all the existing hot and cold side bolt ons and sourcing 26 stuff I found this the easiest way.

In saying that I am more than happy with the current setup, Once the conversion is done you have for all intents and purposes a 26 head which opens up a whole new world of cam shaft options etc. I am currently running tomei 10.25 lift with staggerred duration inlet and exhaust cams. Dan of ERD fame has now developed a vct setup for the 26 head and even better he can apply this to my converted 25 head because most of the gear is already there.

We will be pursuing this setup early in the new year.

There's my experience on the subject. Good luck with which ever way you go.

[NYTSKY]

I have a set of Tomei RB25 Procams with matching valve springs for sale. Brand new in box.

PM me if you are keen.

[The Dan]

Neo heads are the best if you are going custom plenum or staying with the stock inlet and plenum. Can make 1000hp on that gear if you don't want to change it from standard....just port match the inlet to the head you have. The neo heads are solid lifter already but the springs are not going to do the job so a set of supertech double valve springs (I'm 99% sure they do them for neo). You won't make 700hp on a 63mm turbo. You might almost maybe almost get there on a 67 but that would be pushing more than 2 bar I think.

Neo is better also because you can keep the VCT. We do a VCT camshaft set to suit and will be better than any other bolt in option for a Neo for that turbo setup.

Forget port and polish, most people don't know wtf they are doing and the ones that do won't tell you how. Just clean up the intake and make the bowl area less sharp and daggy, most benefits from smoothing the edges of the combustion chamber area around the valve entry and exit to remove the high point that Nissan put there. Don't touch the squish area. It's there for a reason. Removing it is not only a waste of time but you will lose HP. If you want a good V8, port the squish area, those pushrod dinosaurs are so inefficient they'll shit hp out the doorhandles instead of the wheels.

Turning the boost up will not net you any more gains from the amount you made previously. The valve springs just cannot handle the pressure and you will lose efficiency there until new springs are in.

The rest of the setup looks good. By mains girdle do you mean one of the aftermarket billet ones?

They are truly a waste of space. Japanese and Local RB's have been making reliable 800-1500 hp on standard girdles for decades. Don't fix what isn't broken. I have only seen two main bearing failures on an RB. 1 was when the girdle wasn't tightened down and 2 was someone clamping a gearbox up against clutch assembly then forcing the crank to turn when it was seized due to improper fitting. 10k and the mains were shagged starting from the thrust outwards.

It has never been a problem on RB's and never will. If you are busting main bearings, then you have some other problem that needs fixing

If the bottom end is already build with this then leave it, it costs too much to wind back the clock now.

The trust cooler - is it a ~100mm item?

Apart from the aforementioned changes you sound like you are on the right track. I love seeing a good RB25 crack 500kw. Go with the bigger turbo

[stiddy]

Neo heads are the best if you are going custom plenum or staying with the stock inlet and plenum. Can make 1000hp on that gear if you don't want to change it from standard....just port match the inlet to the head you have. The neo heads are solid lifter already but the springs are not going to do the job so a set of supertech double valve springs (I'm 99% sure they do them for neo). You won't make 700hp on a 63mm turbo. You might almost maybe almost get there on a 67 but that would be pushing more than 2 bar I think.

Neo is better also because you can keep the VCT. We do a VCT camshaft set to suit and will be better than any other bolt in option for a Neo for that turbo setup.

Forget port and polish, most people don't know wtf they are doing and the ones that do won't tell you how. Just clean up the intake and make the bowl area less sharp and daggy, most benefits from smoothing the edges of the combustion chamber area around the valve entry and exit to remove the high point that Nissan put there. Don't touch the squish area. It's there for a reason. Removing it is not only a waste of time but you will lose HP. If you want a good V8, port the squish area, those pushrod dinosaurs are so inefficient they'll shit hp out the doorhandles instead of the wheels.

Turning the boost up will not net you any more gains from the amount you made previously. The valve springs just cannot handle the pressure and you will lose efficiency there until new springs are in.

The rest of the setup looks good. By mains girdle do you mean one of the aftermarket billet ones?

They are truly a waste of space. Japanese and Local RB's have been making reliable 800-1500 hp on standard girdles for decades. Don't fix what isn't broken. I have only seen two main bearing failures on an RB. 1 was when the girdle wasn't tightened down and 2 was someone clamping a gearbox up against clutch assembly then forcing the crank to turn when it was seized due to improper fitting. 10k and the mains were shagged starting from the thrust outwards.

It has never been a problem on RB's and never will. If you are busting main bearings, then you have some other problem that needs fixing

If the bottom end is already build with this then leave it, it costs too much to wind back the clock now.

The trust cooler - is it a ~100mm item?

Apart from the aforementioned changes you sound like you are on the right track. I love seeing a good RB25 crack 500kw. Go with the bigger turbo

Yeah I figured the BW 63mm will be too small, ive started looking at the EFR 91-80 after talking with a mate.

The trust cooler is 100mm thick.

Im leaning toward staying with the stock RB25 head because ive already got the exhaust manifold and things for it. Unless the exhaust manifold is interchangeble with the neo?

the plazmaman plenum bolts onto the lower half of the stock inlet manifold so if that bolts onto the neo thats half the battle won.

As for springs am looking at a set of tomei spings. Another mate also has a set of race springs and 290* camshafts that could be interesting, but i'd be interested to hear on your VCT set up??

Yeah its a billet mains cap girdle. I only got it figuring it will help with keeping the thing together, first time (well now 2nd) ive built a jap motor. Its still in its wrapper and might stay there lol. Was a peice of mind type thing.

Id rather a highly strung RB25 instead of a RB25/26/30 conversion or stroker. standard stroke/displacement carrying 30psi and big revs is just the way to go.

Thanks for ya help Elite.

[The Dan]

Yeah I figured the BW 63mm will be too small, ive started looking at the EFR 91-80 after talking with a mate.

The trust cooler is 100mm thick.

Im leaning toward staying with the stock RB25 head because ive already got the exhaust manifold and things for it. Unless the exhaust manifold is interchangeble with the neo?

the plazmaman plenum bolts onto the lower half of the stock inlet manifold so if that bolts onto the neo thats half the battle won.

As for springs am looking at a set of tomei spings. Another mate also has a set of race springs and 290* camshafts that could be interesting, but i'd be interested to hear on your VCT set up??

Yeah its a billet mains cap girdle. I only got it figuring it will help with keeping the thing together, first time (well now 2nd) ive built a jap motor. Its still in its wrapper and might stay there lol. Was a peice of mind type thing.

Id rather a highly strung RB25 instead of a RB25/26/30 conversion or stroker. standard stroke/displacement carrying 30psi and big revs is just the way to go.

Thanks for ya help Elite.

Exhaust manifold is the same, inlet manifold is different at the head but same a the plenum so you should be sweet there.

Having it already solid lifter makes things a lot easier.

What lb specs are the Tomei springs?

[GTSBoy]

You probably shouldn't put a Neo head onto pistons that were chosen to suit a normal RB25.

[stiddy]

Exhaust manifold is the same, inlet manifold is different at the head but same a the plenum so you should be sweet there.

Having it already solid lifter makes things a lot easier.

What lb specs are the Tomei springs?

Sweet, thanks for the info mate. Might have to whack the car on a trailer and bring it up for a visit lol.

I was looking at Lewis Race engines, at his RB heads.. http://www.lewisengines.com.au/category25_1.htm

Seems like a fairly good base to start with. Am also looking at oversize valves. I just want the head done once and done right.

I've got the Tomei B type springs. not sure on lb specs off the top of my head.

Does cam selection change with neo heads? I want big cams, as i said in previous posts atleast 270s if not maybe the 290s from my mate. (hes not using them)

Why would the neo head have any affect on the bottom end? they are a generic RB 86.5mm CP piston.

[GTSBoy]

Why would the neo head have any affect on the bottom end? they are a generic RB 86.5mm CP piston.

Because the combustion chamber in a Neo head is ~10 cc smaller than in a normal RB25 and they use different pistons.

[kitto]

Yep, GTSBoy is correct. Neo uses different pistons.

[JustinP]

Yep you need to get CP to make you custom pistons to suit the Neo engine, none of their off the shelf items will work.

Because the combustion chamber in a Neo head is ~10 cc smaller than in a normal RB25 and they use different pistons.