Rb25 neo bottom end rebuild

[vxsr33]

My r33 gtst has no compression in one of the cylinders and low compression in the others, so i have purchased an r34 gtt bottom end to put in. Ive never done something as big as a rebuild myself (will have mates to help out though).

My goal at the end of this is a freshened up motor and a safe and reliable 250rwkw.

just after a list of parts i will be needing or any advice in general. Should i get new piston rings?

And with headstuds and gaskets should i go for aftermarket performance parts or just standard nissan?

Thanks guys

[Manuel Kasko]

Stock engine can easily handle 250rwkw, been running the same power and 20psi in my R33 for like 4-5 years now.
I wouldn't bother doing anything, save the time and money and just buy a neo engine or a stock Rb25.

You will probably get the same answer from a lot more people.

[GTSBoy]

Don't try to use the Neo pistons with a 33 head though....

[vxsr33]

Don't try to use the Neo pistons with a 33 head though....

why cant you use the neo pistons with the r33 s2 head?

[GTSBoy]

Um....Neo pistons suit a head with a 51cc (or something like that) combustion chamber volume and R33 pistons suit a head with 63cc (or something like that) combustion chamber volume.  Horrible compression ratio problems will ensue if you try to use one with the other.  In one case you get compression like in a 1932 Fergussen tractor.  In the other case you need to use rocket fuel to stop it from pinging itself to death.

[vxsr33]

Oh damn[emoji54]
So the only issue is the pistons? Would swapping them to aftermarket ones make it compatible?

[GTSBoy]

Well, yeah, you could.  But once you get to that level (ie dismantle, machine the bores, get pistons, balance rotating assembly) you are no longer doing the simple "buy this half and bolt it to that half" build that your OP looks like describing, and you are now into a build that has enough work in it to justify doing stuff more thoroughly.

You'd be better off getting a Neo head or getting a whole Neo (or a whole 'nother R33 engine) and selling on the short motor you already have.

[vxsr33]

Thanks heaps for the input. I think i will keep my eye out for a neo head for a while and if not sell the shortblock.

[admS15]

Thanks heaps for the input. I think i will keep my eye out for a neo head for a while and if not sell the shortblock.

Or rb30 bottom end and bolt your head on. Will gain a heap of torque and probably work out cheaper overall.

[vxsr33]

Or rb30 bottom end and bolt your head on. Will gain a heap of torque and probably work out cheaper overall.

Hmm, would consider doing this, but how hard is it to do? im assuming there is a fair bit of machining and custom work involved? I have a budget of around 2k max. I will check out the rb30 conversion threads though.

Thanks

[AngryRB]

Its very easy, find a running RB30 and do it, the guide makes it straight forward, will start mine soon hopefully, is from working RB30 so im confident..

[vxsr33]

Anyone know if i could bolt my standard 33gtst gear up to a neo head?

[Dose Pipe Sutututu]

why not?

[WMDC35]

Yes you can

[vxsr33]

Would the intake manifold ports on the r33 line up properly with the neo or are they different?

[AngryRB]

The runners on the R33 intake manifold are larger so would create a step, pretty sure the Gasket is identical on both heads though.

[vxsr33]

The runners on the R33 intake manifold are larger so would create a step, pretty sure the Gasket is identical on both heads though.

So i would probably need to get an r34 plenum and intake manifold aswell then? Seems like it would negativey impact the performance of the motor otherwise.

[KiwiRS4T]

Get rid of the step with some kind of grinder or dremel.

[AngryRB]

Yeah im not sure if its an issue or not, maybe the head can be port matched or just go the R34 manifold.

You'll need top feed injectors and rail if going neo manifold, plus possibly an adaptor plate for the IAC ( i did), plus R33 throttle body needs modified.

[WMDC35]

42 minutes ago, AngryRB said:

The runners on the R33 intake manifold are larger so would create a step, pretty sure the Gasket is identical on both heads though.

Ports are the same, seems strange they'd bother to make the head/ports different but then use the same gasket?