GTR intake plenum on RB25

[Warpspeed]

Oh golly, what a bun fight.........

My take on it is this. Multi throttle bodies will give you two things, better transient throttle response, and better cleaner idle with large overlap cams. None of this is going to show up on a dyno at wide open throttle(s). On the road it might feel quite different, and that is where the advantage lies, not on the dyno, or quarter mile times.

For sheer balls to the wall top end horsepower, a single throttle body can be made as large as you want to make it. Throttle response and drivability will not improve. Drag cars have single throttle bodies, and the road racers keep the individual throttle bodies. What do YOU want to use YOUR car for ?

As far as inlet manifolds go, what else are you going to do to the engine, and what is most important to you ?

Long intake runners are a definite advantage for low end and mid range torque. At stock and moderate boost levels they are NOT restrictive as Sydneykid keeps on telling everyone. Air distribution is excellent. If you are planning absolutely massive boost and radical high Rpm power, something else might work better.

The GTR manifold was designed for less restriction, but it also is going to have less low and mid range torque because of much poorer cylinder filling off boost. That DETT engine relies totally on boost pressure to make it go.

I would bet that with stock boost and stock single turbo, an RB25DET will have reduced low and mid range torque, and it will not have the same top end power as the GTR simply because the stock turbo will run out of flow. Although I have not actually tried this myself.

It probably will work better if you are planning to upgrade everything else along with the intake manifold, the engine will then take on a completely different character.

At stock GTR power levels the factory GTR manifold will have near perfect air distribution. The Nissan engineers made it that way by putting in all those ridges, steps, and curves. But if you start increasing the air velocities greatly above what it was designed for, it will all start to go wrong, and the rear cylinder runs lean.

That is where all this nonsense started, guys start running 20+ psi and complain the stock manifold is rubbish. Well, maybe, but it was never designed for that.

Decide what you want it to do, and design it to do that job.

[N I B]

ND4SPD is a genuine road car that had to do everything and has run faster after the story was done near 1 year ago we how want to go for broke at the strip but it has run 142mph over the 1/4.

[Sydneykid]

That is where all this nonsense started, guys start running 20+ psi and complain the stock manifold is rubbish. Well, maybe, but it was never designed for that.

Excellent post Warpspeed, I would only like to add one little bit to the above para....

The Gibson GTR's ran the standard plenum and throttle bodies and the only engine dyno sheet I have seen showed 640 bhp at 1.9 bar (28 psi). So if 13 years ago they could get it to work perfectly, run 1,000 kms at race pace, up and down MtPanorama, surely it is not stretching the imagination for us to do the same now. Just the ECU improvement alone is light years ahead. :burnout:

[sweetr33]

WARPSPEED- Good explanation mate, The reason i have got the GTR plenum sitting in my shed over the Greddy on or custon one of stock runners is because i bought a big package when my engine blew, consisted of afew gtr parts including crank, rods, plenum, injectors and fuel pump n rail, also came with lots of other goodies, for me to get all these goodies at a good price i had to buy the lot. Everything is usable on my rb25 and therefor i have a gtr plenum that i am going to adapt to my head and see how she goes, thats why this thread was started. I understand that for the low-mid range torque its not going to be benificial and maybe not significant gains in top end power i havent a clue but since i got it i am going to use it seem logical? I got head port work, 256 cams therefor retaining vvt, to try n help with the breathing alittle. I think its better to put it on now whilst i have the engine out and in pieces rather than trying to swap manifolds over months down the track when the engine is in the car and driving.

[lukevl]

See through all this bickering, a lot of good points have come out. You just have to sift through some people's crap first

[Warpspeed]

Sweetr33, sounds like you have a plan.

Fitting the GTR plenum just by itself will probably make the engine feel a bit soft down low, and might be a disappointment. But if it is just the very first step in a long range plan that you have worked out, it is probably a pretty smart move.

[BBQ]

WARPSPEED- Good explanation mate, The reason i have got the GTR plenum sitting in my shed over the Greddy on or custon one of stock runners is because i bought a big package when my engine blew, consisted of afew gtr parts including crank, rods, plenum, injectors and fuel pump n rail, also came with lots of other goodies, for me to get all these goodies at a good price i had to buy the lot. Everything is usable on my rb25 and therefor i have a gtr plenum that i am going to adapt to my head and see how she goes, thats why this thread was started. I understand that for the low-mid range torque its not going to be benificial and maybe not significant gains in top end power i havent a clue but since i got it i am going to use it seem logical? I got head port work, 256 cams therefor retaining vvt, to try n help with the breathing alittle. I think its better to put it on now whilst i have the engine out and in pieces rather than trying to swap manifolds over months down the track when the engine is in the car and driving.

Are you still running the stock ECU ?

[sweetr33]

power fc,

[BOOSTD]

Why not tell us who you are SK so we can see if you are what you claim to be as you have posted a few Facts that have been anything but so i feal its time you name your self.

LOL My tricyle would drift much better with a square frame rather than cylindric!

[DoughBoy]

Have a guess who has the fastest GTRs in WA?

Some drug son of rajab?

[BBQ]

power fc,

Ok what power fc are you running ? RB25Det ? Or Rb26dett ?

[sweetr33]

rb25det power fc, already spoke to matty spry from P.I.T.S and he said there wont be any dramas.

[N I B]

Seen how many Jap circuit race cars have single throttle bodys now.

AS for the oz race cars that was a very long time ago and to group A rules so even if they wanted to change them they can't under group A.

Ask John munro about ND4SPD and you will see its a genuine streeter but we are going to change the car around for a few months to show its tru performance as it has run 142mph down the 1/4 on basic dunlop road tyres wait till we set up the chassis and run semi drag rubber + good fuel and race tune.

[sweetr33]

Ok Updating, Me and dad went and had a closer look at the gtr manifold. Seems the gtr runners where they meet the head are round where the gtst inlet port shape is sort of like a butterfly shape, Our theory is to chop the standard gtst inlet manifold about 2 inches from the flange to the head, retaining the water cooler feature, which would also make the part where wer need to adapt the gtr plenum also round following so far?

There was going to be a drama fitting the injectors into the gtr plenum, meaning we had to drill holes into the runners and make alloy sleeves to fit the injectors and get the right angle of fire etc, but now with retaining the standard inlet flange we already have hoels for injectors and also a good spray angle with the aid of the inlet water cooling.

Another drama we came across with the initial thought of just making an adapter plate was that the gtst inlet ports are wider than the gtr plenum holes so we would have to somehow taper down the the correct size. Was going to be a hassle so we have decided this is the best way. Let me know what u guys think and know about our idea

[Warpspeed]

This has been done before by many people. The way they do it is as you suggest. Cut all the GTST runners off straight, just before the injectors, and either weld on the GTR plenum direct, or better still, weld on a flat flange plate, and then bolt on the GTR plenum.

There will be quite a bit of grinding and matching because the runners DO NOT LINE UP perfectly. GTST runners are almost evenly spaced, the GTR plenum has the runners spaced in three pairs to suit the three twin throttle bodies. Every runner needs to be moved sideways a small amount. This is not obvious just by quickly looking, but if you look very carefully you will see what I mean.

[lukevl]

You will come across the problem that cylinders 3&4 dip down on the RB25 lower runners to make them equal length. This to me seems like the biggest problem.

***Does anyone have an RB20 lower runner section that they can look at for me!!!****

[browny]

Do these help?

[lukevl]

I'm going to have a red face I can tell but... what is that? Some sort of wild mods to the 5th and 6th cylinder?

[Sydneykid]

I'm going to have a red face I can tell but... what is that? Some sort of wild mods to the 5th and 6th cylinder?

Nah, #5 and #6 are different to clear the master cylinders, brake and clutch. As you can see they are the same close to the cylinder head, so you can cut and weld on a flange.

[browny]

Thats the lower half of a std RB20 inlet manifold.

I think the last two runners are moved inwards to allow clearance for the clutch cylinder (someone with a skyline will be able to confirm or deny this).