GTR Plenum V Greddy Plenum

[sweetr33]

Hey i was ondering if anyone would be able to share some information on the gtr plenums and the greddy plenums in terms of flow characteristics and efficiency etc. I got the gtr plenum which we are adapting to my RB25 head. In long term chasing a max of 450hp at the wheels, im not really concerned about the gtr plenums efficiency as there ar many gtrs that make nice numbers still using original plenums so im assuming there good. Any advantages going greddy over gtr?

[GTS-t VSPEC]

What are you doing with the multiple throttle bodies, or are you converting to single?

[sweetr33]

converting to single.

[GTS-t VSPEC]

Ok, sounds like a good idea. I would think the GTR plenum will suit you fine for up to 450rwhp.

[sweetr33]

what plenum were u running gtstvspec?? U made that sort of power??

[GTS-t VSPEC]

I'm running a Greddy plenum on a RB25 head and making 450rwhp with a GT30 turbo.

[sweetr33]

well im going to have to stick with what i have for the moment, i cant see there being any dramas with the GTR plenum. Single 85mm throttle body is probably the choice too. Im not expecting to make any big power till i can upgrade from a high flow to a bigger turbo. I havent done much research on gt30's etc, im more hooked on TD06-25Gs or T04R but will see thats a fair way down the track as i spent all i could on the motor and motor accessories getting it strong.

[GTS-t VSPEC]

I'm sure it will work out fine, good luck:D

[N I B]

The plenum will work sweet but a GT30 will kill the TD06 for responce.

[Sydneykid]

Hi sweetr33, just in case you haven't seen or done the numbers for yourself, here is the comparison between a single 100 mm throttle body and the standard GTR multiple (6) throttle butterflies. Also following are some comments I wrote a while ago on this subject.

Butterfly = 44/2*44/2*22/7 = 1,521 sqmm

Spindle = 44 * 4 (from memory) = 176 sqmm

= 1,345 sq mm each X 6 = 8,070 sq mm

Compared to the big single.....

100/2*100/2*22/7 = 7,857 sq mm

Spindle = 100 X 6 = 600 sqmm

= 7,257 sqmm

So, the standard 6 throttle bodies are 11% larger than one 100 mm single throttle body.

But is this the right way to do the comparison? Since each cylinder fires individually (one at a time) then isn't each cylinder getting sole use of the 100 mm throttle body some of the time? Not all of the time because of valve timing overlap between cylinders and the volume of air contained in the plenum. So you would have to know the valve timing and the plenum volume and the engine rpm to work out each individual cylinders share of the 100 mm.

My opinion (for what it's worth) is that the main reason the Japs go to a single throttle body is so they can use MAP sensor driven ECU's. Multiple throttle bodies and MAP sensors don't go together very well, especially when you have big cams and lots of boost. Over some LARGE horsepower number, there is probably an airflow advantage, but I have no idea how LARGE it is.

What I can say for certain is there is far better throttle response for the GTR multiple throttle butterflies. Personally I have yet to see any power advantage from a 100 mm single throttle body and we are well over 625 bhp in our circuit race cars. I should also point out that the Brisbane Street machines R32 GTR runs 9's on radials with the standard GTR multiple throttle bodies.

Hope that helps

[Leewah]

I'm still running the stock plenum with multiple throttle bodies on my car and we made 617rwkw on my GTR at AutoSalon back in April.

The only reason I would use a single is for ease of tune.

The multiple throttle body is so much better for street response.

[BU5TER]

Good choice with the TD06 25G, I haven't seen any car with a GT30 come near my old TD06 set up

EDIT: sorry by any car I meant RB25 with GT30

[GTS-t VSPEC]

Buster, What did you get from your TD06 25G?

[BU5TER]

11.8@128mph in full street trim or 11.7@128mph with 16" rims/nittos and full street trim

[GTS-t VSPEC]

Oh sorry, it thought you were reffering to power output:D

Why would RB25's work fine with single TB and yet RB26 suffer from repsonse issues?

[BU5TER]

476rwhp on Shootout 03 last year 19psi, pump fuel

[GTS-t VSPEC]

Damn, that's impressive, I hope to do more than that with the GT30, but will be at higher boost.

Back to the single vs. multiple TB debate. Has anyone attempted it and recorded any useful info on the difference in response?

[sweetr33]

ok, the multiple v single tb thing. I am going to stick with the single, although i was referring to a 85mm single tb and the info was given at 100mm tb would the response be better from the smaller throttle body? I was reading on these forums that munro's street gtr is using a single 85mm tb insted of multiples???

[N I B]

Did you also work out what harm 6 10mm shafts do to airflow and the area they take up in your smallish intake runner or seen and heard them on a flow bench, The scream they make is amazing.Never seen any car respond faster than Pauls 100mm single on a Greddy manifold.Try before you knock it SK you WILL be amazed,then you can coment with athority.

[Sydneykid]

Did you also work out what harm 6 10mm shafts do to airflow and the area they take up in your smallish intake runner or seen and heard  them on a flow bench, The scream they make is amazing.Never seen any car respond faster than Pauls 100mm single on a Greddy manifold.Try before you knock it SK you WILL be amazed,then you can coment with athority.

Steve, I have "tried it" both with a standard RB25 throttle body and a Foulcan throttle body. I could fee lthe slowness instantly on the road, and on the track it was disasterous. With the dog box we have ~50 milliseconds for a downshift and you MUST match the engine rpm with the gearbox rpm. Otherwise you end up with twisted splines on the input shaft from the triple plate clutch and missing teeth on the gears, particularly 2nd.

It is quite simple to understand why this is the case. With the multiple throttles there is very little air between the butterflies and the inlet valves. So when you close the throttle the airflow to the engine stops instantly, therefore so does its power production. Compare that to a single throttle body with a plenum in between the butterfly and the valves. The usual rule of thumb is at least double the engine capacity in the plenum, so on a 3.1 litre that's 6.2 litres. Plus that 6.2 litres is under boost just before you close the throttle, so at 1.5 bar it really has 9.3 litres of air in it. In addition, after you close the throttle, the plenum goes under vacuum, around 0.25 bar is not unusual, that's another 1.6 litres.

So when you close and reopen the throttle 7.8 litres of air flow dulls the response. On a 3.1 litre engine that's almost 5 revolutions of the crankshaft, at 7,500 rpm that's 666 milliseconds. That's more than 10 times slower than the gearbox will handle. To translate that into distance, at Bathurst it would mean we would be lapped twice during the race distance

Another way to look at it, Nissan designed the GTR to win races on the circuit, if they thought a single TB was better then they would have used it. Let's face it, a single TB is simpler to make, therefore cheaper, easier to tune and maintain. But Nissan went for multiple TB's, why? Because for their stated aim it was superior.

Let me close off with;

I have seen articles on Jap GTRS that run low nines still using the original 6 throttle bodies & a std plenum!!!