R33 GTST Plenum/intake manifold.

[Guest DON91E]

Heya Sexy ppl, (yes and the ugly ones too )

I have a R33 GTSt, im planning on making a custom intake manifold with the help of my dad the tig welding maniac

Just need to know first but,

Would a R33 GTR plenum fit rite onto a R33 GTST?

im planning just drill a hole @ the bottle of the plenum and weld up a 2.5inch/3inch stainless pipe to the newly drilled hole.

Could be worth it? could be a disaster?

Only time wiill tell

anyone else tried to be a hero? any storys? anything i should avoid?

Donnie

[TTT]

Isn't that going to make the back pistons f**K up cause they won't get as much air?

The standard one is there cause it is in the middle and distributes the air evenly.

You're choice though.. However, I don't think that it's as easy as blocking the original hole and drilling a new one at the front.

I think that this is going to end up in tears.

[Warpspeed]

Nizpro in Melbourne make an inlet manifold top half that has the throttle body at the front. Sub Zero in Queensland can supply a similar (but different) setup. If you can find a GTR six throttle body setup complete, this will also bolt straight on as well.

I think you should be able to do any of these for around $A1,000 to $A1,600, or as you say, fabricate someting up yourself.

The Nizpro system has long intake runners, about the same as the original. The Sub Zero system has a very large plenum with shorter runners. The GTR has very short runners, and a mid sized plenum.

Which is actually best for power, and off boost throttle response depends on what else you do to the engine, and what you want.

[Guest DON91E]

o so the gtr plenum will bolt straight on?

See i heard alot things like No they won't and yes they will with some modifying,

I mite look into this further

Donnie

[Guest Nismo_Freak]

Longer runners are better for off boost response and torque. Longer runners also will give better low rpm torque but will sacrifice top end power that can be had with short runners. By tapering the manifold into a tear-drop shape you can effectively speed up air flow to the two rear cylinders to ensure they are getting enough air. The plenum needs to be about 1.5 times the displacement in volume. I would go with a moderate length runner to maintain low-end and give decent top end gains. While your at it polish the head's intake ports but dont port them, its too easy to mess up. Be sure to match the port diameter with your runners. And get some DYNO #s on your design!

[Warpspeed]

Some very wise words from Nismofreak.

A lot of guys have done this, and I already have the full six throttle body setup myself ready to go onto an RB25. In my opinion it is by far the best and neatest solution.

Beware though it comes in several pieces. There is the plenum, three dual throttle bodies, a short inlet manifold which holds the injectors and thermostat housing, and the fuel rail. Make sure you get the lot together though.

There are people replacing the six throttle body setup with the Trust super plenum, and large single throttle body. You see the plenum and six throttle body setup advertised for sale, sometimes with a fuel rail, but never with the inlet manifold part.

Some poor bastard will buy this, and then find he is missing a vital part which is difficult to obtain separately.

[Guest DON91E]

Hmmm,

But i noticed on my mates CA18DET that his one is similar. Rather than runnin across the engine his one drops rite down Not unlike the SR20DET.

So this being so, woudn't this fudge up the back 2 pistons as GTST was mentioning?

How can this be so on the SR/CA but not the RB?

So this is going to pose a problem?

(can't wait to hear response)

[Warpspeed]

You can be sure that an end throttle body plenum designed by the original manufacturer is going to have reasonably good air distribution between cylinders.

If you look inside you can often see ridges, humps, steps, and all sorts of design features to ensure equal air distribution. The designer is interested in emmissions and fuel economy, if not absolute maximum power.

The air velocity in the plenum will also not be extremely high in a stock motor.

Trouble starts when you try to get twice or three times the power out of the same motor using a stock plenum. The air velocities go up a fair bit, and things start to wrong with the air distribution.

That is why very large plenums are often fitted to high power engines, and work well, even if the individual port runner sizes are no bigger.

Any serious engine is going to have a fair bit of airflow work carried out on the cylinder head, and matching the airflows with the plenum fitted is all part of this.

[Guest DON91E]

So should i or shoudn't i?

[Warpspeed]

My first choice would be a GTR setup, which is what I now have.

If your going to fabricate your own plenum to fit on top of the existing manifold lower half, that would also be a very good setup. The most important feature is to have large well developed bellmouths, where the intake runners enter the plenum. And make the plenum volume fairly large as well.

This is exactly what you can buy off the shelf from Sub Zero, apparantly a very good modification from what I hear.

[turbomad]

Hey Warpspeed have you fitted the GTR plenum yet, I'm curious as I always thought the GTR head was different therefore the plenum and turbo manifolds won't fit, let us know ok.

[hungry6]

on my last set up was a modify of the existing plenum and it made a huge dif with heat soak and response. beside everything ppls say here u will also need to get custom throttle cable made and relocate where the cables hook up to. also the throotle body have to be turn upside down for it to work. and the gtr plenum

DOES NOT FIT

[Guest DON91E]

:confused:

Hmm ok, Can we get a final resolution to this.

Will a R33 GTR plenum fit on a R33 GTST,

Alot of diff answers from alot of diff ppl.

DOnnie

[Warpspeed]

Well I have the GTR throttle body setup, but no car to try it on.

My understanding is that it will not fit onto an RB20, as the head is quite different.

The actual head castings for the RB25 and RB26 cylinder heads are identical. Same ports, same valves, same water passages, same everything. There are a few very minor machining differences though between the two.

I have been told by several very reliable people that the inlet manifold will fit straight on, but the dual GTR exhaust manifolds will not. But because the castings are the same, four of the exhaust studs can be easily moved.

I have magazine pictures of an RB25 with the GTR inlet setup, this was a Nizpro project a long long time ago.

But no, I have not actually done this myself - Yet.

[rev210]

Originally posted by Warpspeed

Well I have the GTR throttle body setup, but no car to try it on.

My understanding is that it will not fit onto an RB20, as the head is quite different.

The actual head castings for the RB25 and RB26 cylinder heads are identical. Same ports, same valves, same water passages, same everything. There are a few very minor machining differences though between the two.

But no, I have not  actually done this myself - Yet.

It's not a bolt on mate. The RB20DET and RB25DET have the same inlet/zorst positions the RB26DETT is different on both sides.

You can 'make' it fit with a custom made spacer plate and some grinding. Cool if you have a workshop near you that has already done this, not cool if it needs fabrication and you can't do it yourself.

BTW. The position of the 3 (dual) throttle boddies is a bastard to get properly set if you have moved them from factory, but they usually mark them with a pen just in case. I would run a mile to avoid trying to reset the throttle position from scratch (carbies are bad enough).

[Warpspeed]

Thanks Rev, no worries on the workshop facilities. I have a bridgeport mill at home, so can make the bugger fit no matter what!

But, as this has already been done by others, it cannot be too hard.

Well aware of the throttle body synchronisation difficulty. These are an original matched set still locked with a dob of factory white paint on the threads.

Cleaned up with all the oil grunge and carbon removed, I can just see the faintest bit of light through each throttle when shut against the stops, so should be o/k. Thanks for the advice.

[CHCH_gtst]

i know for a fact that the rb20 and 26 are different, weve got both these heads at work at the moment, and ill have a 25 on my bench tommorow so ill do some measuring.

[Sil8ty]

Will the RB-25 with the GTR inlet manifold on it (if it fits) still be able to maintain the std management?? What about when you do a custom plenum, as i am half way building one myself, i guess it would if you maintained all the factory sensors/fittings etc??

[Warpspeed]

Well the six throttle body manifold does all the same things that a stock manifold does. It is just a totally different shape.

I bet all the standard features such as TPS, fast idle, PCV , air and water temperature sensors, and so on are all still there. I would also bet that the same sensors and plugs are used, but may need to be moved a bit. Same with the throttle cable and water hoses.

It may all look a bit frightening, but may not be that difficult to sort it all out one step at a time, if you can figure out what it all does.

[Sil8ty]

Warpspeed: When you use the GTR Manifold on your GTS-t are you using std management. Let me know how you go!!!

As i am very interested. Mate has a std GTR manifold in shed, doesnt use it so i might go steal it :lol: