Neo Head Help...

[Damien2]

I wanted to use a neo head on my series 2 gtst. I've searched for hours on different forums but couldn't find the answers I'm lokking for.

1- will my greddy plenum and 6 boost manifolds fit onto a neo head?

2- what are the complications with doing the neo head conversion apart from the raised compression ratio?

Currently the car is running 360rwkw on stock motor and I wanted to start building an engine on the side to drop in when this one gets tired.

I don't want to start changing manifolds. I'm budget conscious but I also understand its not going to be cheap.

The head I was looking at was the lewis engines rb25 neo ultimate head package.

My application is mainly just eventually just a crazy weekend street car and monthly drag car.

I will eventually chase more power but for now I will just go to the limit of my gt3582r.

So basically I want to do it in stages as money becomes available.

Any help would be greatly appreciated.

[GTSBoy]

Ex manifold same. Inlet ports different shape. Would therefore benefit from correct inlet manifold.

Having to change manifold shouldn't be a problem. Simply buy new manifold, and sell existing one after the swap is done.

There are also various sensor differences that you will want to take into consideration, depending on what ECU you're using.

[discopotato03]

I have not seen them side by side but I seem to remember people saying that R33 and R34 RB25DET inlet manifold gaskets are the same , something to check on .

If I was building up another engine I'd leave the Neo head for that one and get pistons to suit it . Maybe even buy a complete Neo to rebuild .

A .

[Damien2]

Ok thanks guys. Much appreciated.

[GTScotT]

GTSBoy is correct.

Exhaust is the same, intake it different.

Be mindful that NEO's have a different piston shape to accommodate for the combustion chamber size. Simply installing a NEO head on a R33 RB25 will result in an unknown compression ratio, potentially making the motor more detonation prone and counteracting your efforts.

Consider the value in the swap before proceeding. The R33 head has proven a good performer all the same.

Edited April 7, 2014 by GTScotT

[too_much_boost]

I have a neo inlet gasket which seems to fit up perfectly with my Freddy R33 manifold.

[Griffin]

i have fitted r33 inlet manifold to a neo head. all bolted up fine.

[Damien2]

Wow... back to being confused. Lol

[LaurelPWR]

The bolt patten is the same but the ports are heaps differant

[Gillyr33gtst]

Hello this is my first post/reply early model neo engines 1997-1998 versions share the same ports and cas as s2 r33 so all manifolds are interchangeable only major difference is the rear oil seal seat you will need neo flywheel r33 flywheel fouls on it very easy conversion to do no wiring changes just flywheel hope this helps

[iruvyouskyrine]

Are you taking about the rear main seal? All RB's use the same rear main and I am running a RB20 flywheel on mine with no issues.

[Gillyr33gtst]

Rear main seal that bolts to back of the block when I converted from s2 25 to neo that was the only issue

[iruvyouskyrine]

So not the actual seal but the metal retaining unit?

[Gillyr33gtst]

That's the one mate sorry for the incomplete detail I'm in hospital on pain killers probably should have waited till I got home hahaha

[GTSBoy]

I'm running R32 flywheel on Neo also. No fouling.

That particular "early Neo" situation is a special one I think. I don't think that those engines are true Neos. These are the ones that were seen in some of the Stageas around that time, right? They look like a cross between a R33 and R34 motor, with nothing looking quite right.

[Gillyr33gtst]

Correct was unlike the s2 engine or for a fact any 25 I've worked on.i will post when the I pull engine out again this week for a kero build I'll take pics of rods pistons head oil pump and lifters just for reference purpose the block has two oil returns as well so will be good to see what you all have to say and what is meant by true neo

[GTSBoy]

Good idea. I'm sure the information on them is already around here somewhere, but finding it might not be easy. Another post with the info you plan to get will be welcome.

For reference, when I was looking for a Neo for my R32 a local Jap wrecker had one of these engines. I had a look at it, decided not to touch it. The concencus from a few people I asked, one of whom is my bro-in-law who runs a performance workshop and has played with nearly every such engine, is that these "not true Neos" are just that. I think they are old 25s with a few Neo looking bits and pieces on the outside. Not the small chamber, solid lifter head.

[Gillyr33gtst]

Cheers for putting me strait about this apparent gap filling engine I never pulled it down before I put it in was just a cheap thrash engine and copped it for a year so will be very interesting to compare pics of rods heads and generally the whole engine I'll hopefully post it by early next week my health will be the only hold up cheers GTSaboy for your input

[Toff]

I have just fitted a Greddy plenum to my NEO And the intake ports are the same, Bolt holes are in the same place, And sitting the gasket on both shows they are in the same place.

[iruvyouskyrine]

Yep that's correct. Everything fits except the IACV, of which you can contact Ben C34 on here for an adapter to use the neo one, or buy an R33 RB25 item and do a little bit of wiring.