Custom Gtr Drag Plenum ** Pics Inside**

[Roy]

Well based on the pics you have posted here, it will be interesting to read the results, a before / after would be great. Unless there are photos missing from the series you have posted, there are areas that i would think could be improved. Have you dont any testing/numbers based on engine displacement, rpm, runner lenght and diameter?

Plus the ID of the runner to the std flange looks like it could do with a bit more work as there appears to be a shoulder there...anyway, these manifold debates always cause arguments...

Edited August 22, 2005 by Roy

[JDMfantasy]

I'm sure the owner of the car will post some dyno #'s once the motor is back in the car, so we'll have to wait and see on that.

We wanted to use velocity stacks, but at the time we could not find any in the size we needed. I've located some now of course, but...too late

What areas would you improve on Roy?

I agree with you on the runner to stock flange, it is a bit of a step down. The head has been ported significantly, so the stock flange will be opened up to match, and that will take care of the step.

I hear ya there....intake manifolds are one of those areas that are still up in the air. Stack vs no stacks, plenum volume and so much more....we do the best we can to make a quality product, but there's always someone out there who can do it better. Does that person then make somthing better?...nope. Even if they did, who's going to test the two back to back? I guess we'll never know. All I can say is that for the goal of the car, I think this manifold will get the job done.

[discopotato03]

If anyone seriously wanted a twin plenum RB26 type inlet it could be done before the six throttles , its function I guess would be slightly better air distribution to 5 and 6 .

Like Roy , not here to flame , I wonder about the plenum form of the Jap style manifolds as in where they curve in half way down the master side . From what I've seen of factory manifolds and intercooler tanks they go to a fair bit of trouble to follow an outside radius to distribute air over a large area ie intercooler core or inlet manifold runners .

I guess you build what people ask for and many think if it works on Terrakumis 1500 hp planet mover its just apples . This is not intended to be an insult just one persons view of the drag fraternitys monkey see monkey do thing .

Cheers A .

[r33_racer]

Plus the ID of the runner to the std flange looks like it could do with a bit more work as there appears to be a shoulder there...anyway, these manifold debates always cause arguments...

<{POST_SNAPBACK}>

That is true, and true again, manifold subjects are very controversial and debatable...everyone has their different 2 cents.

Parts like that can either lose power or help make it or reduce restrictions but there is always another area to help make more power and there is generally no perfect one item that will give power through every range of testing..eg big HP turbo with NA response

[JDMfantasy]

Discopotato, I see what you're saying...but you question the shape of the plenum based on what? There are no back to back dyno numbers on any manifold, so what can you really compare? Obviously this manifold will do what is supposed to do....flow lots of air. Is there a better design? No question. What is the better design? I don't know the answer, do you?

We could build any number of different style manifolds, but who is going to test them back to back on their car?

Also, saying that stock manifolds and endtanks are the best at distributing air is almost comical. The stock RB26 manifold is a tube with a slight taper in the rear, not a shape for ideal distribution of air. Like I stated before, we build our manifolds around a goal, and we build what we feel will best meet that goal.

It is a generally known and accepted fact that a taper toward the rear of the manifold will speed up air velocity, allowing the runners furthest from the TB adequate air. For that reason, our manifold gradually tapers toward the rear. It has gradual curves compared to other manifolds. The TB directs air towards the center of the plenum, not down the backbone, nor the first few runners. It has large runners to flow lots of air. I guess what I'm getting at is how is this manifold simply "monkey see monkey do." There's only so many ways to shape a manifold, everything looks similar.

What would you suggest that would make for a better manifold for a drag motor? (obviously twin TB's may be better for air distribution, like I said, thats what I wanted to build...)

Again, our manifold is not "perfect". What is perfect? Without knowing any facts as to what truly is best, how can you complain about ours? Question the design all you want, but without any evidence to support anything, who cares....

I hope you can see my point. Here goes the controversy

[r33_racer]

Hopefully you will achieve the goal adequately then. I think the general expectation is that every a/m manifold made is required in everyones mind to be practical, easy to construct/fit, relatively cheap (-1500) and will increase response, hold more air, flow faster and distribute air to each runner perfectly even thus satisfying almost every aspect of 'the perfect plenum' for every situation. Cause most tyre kickers want their car to drift, drag and circuit to the level of D1, Top fuelers and v8 supercars which wont ever happen.

However maybe in 10 years when fuel costs $10-15 a litre, the perfect plenum will be available, when were all driving around in oversized remote controlled cars!

Hope it works out for the car its going on..would be good to see any sort of info on it when its tested out.

[WHITER33GTS-T]

I am interested to see how this goes. Is this just a one off or are you going to make more?

[Turbine]

I would not build a manifold based on looks. It is a large capacity plenum with large runners and TB because a ton of air is being moved through it. The runners are 51mm ID, and they taper down to the stock flange (this speeds up air vel.) which will be port matched to the ported head. The opening of each runner is radiused out to from 2" to 3.5" for max flow and smooth transition. This is not going on a street car.

Thats sounds all very well. But when I look at the direction that airflow is travelling, your biggest problem is making the air turn a corner (90* in fact, relative to the intake port direction). Also their looks like their is no internal ducting in the plenum, so the rear cylinders get more air than the front cylinders. You can add more fuel to the rear to even up the mixtures in the cylinder, balance it that way but it's a band-aid approach for a physically (aerodynamically) balanced engine. If its a drag race only car, why dont you use all that engine bay space and redesign it. So what if nobody else can use it in a street car, at least it will work.

Just my opinion buddy

Turbine

[discopotato03]

Fantasy I am not complaining about your manifold , if it does the job for its owner then its a success . The fact that I might approach it in a different way is merely subjective .

A .

[ISL33P]

i just found this after being on a US site and seeing them there. are there any flow results especially variance between runners.

looks like they would weigh a tonne using 8-10mm alu plate. i use 3mm pressed sheet and have not had one blow apart yet.

[33SOM]

Its looks exactly the same as my subzero built one but with a different throttlebody.

[RichyR32GTR]

Wouldn't the easiest way to test plenums be to rig up 6 individual high temp sensors in each of the exhaust ports straight after the head? After getting each injector flow tested and calibrated for exactly the same flows. Same flow from injectors + different cylinder exhaust temps = bad plenum. You'd need to know how your plenum is working / not working to be able to change it though. Then you have different pressures (diff turbos) affecting ait distribution. Hmmm.. like you said before... Too hard basket

[ALL GTR]

Hmmm looks alright nothing special.

Wait till I get my engine back in the car and we'll show you a decent looking plenum. 8-10mm alloy is a waste of time. No more than 5 ill be using 3mm on mine it'll be stainless though.

The trumpets are a much better idea like the ones I have on mine it flows better into the ports. A spreader plate also straight down the middle to divide 3 cylinders helps too.

[ISL33P]

those trumpets need to have a completely rolled bellmouth/bead to be even better than what you claim.

stainless is not the most friendly material when building inlet manifolds. its tendency to retain heat would be the most unattractive feature, especially on the inlet side of a force fed engine.

as for the single divider, good in theory, but they have a tendency to reduce flow to the runners either side of the ports. but best of luck, something new is always good. if you were to run splitters i would recommend two spliters and pair the cylinders as there will be sufficient area either side of the splitter (and bellmouth) for the port to draw air from, which would not be available with a splitter between 3 & 4. a little bit more work would be required but the end result is what counts.

Edited September 4, 2005 by ISL33P