Street Car Peak Power Where Is Best

[GTSBoy]

I say it again.  It doesn't matter what shape or size you make your plenum.  The range of different runner lengths amounts to precious little.  You can go short, like a Greddy style, or you can go as long as the original lower manifold like the Plazmaman plenum....and that's just about the extent of it.  The difference in tuning for peak torque between that lot is noticeable, but only a few hundred rpm really.  Nothing like the choice between your lower and higher options with 2000 rpm between them.

The only option you would have would be to rhink way outside the square that people already work in and make some really long runners that go up and over the cam covers to a plenum that runs along the length of the exhaust cam cover.  Would be a bit ugly, and would probably be a squeeze, and would probably suck with a high mount turbo.  But at least then you could push the peak torque rpm down.  (ie you could at least work toward offering people a real choice as per your original post).

But really, we're talking about turbo engines here.  The turbo is far more important.  Making the boost threshold as low as possible by correct exhaust manifold design and turbo selection is far far more important and effective than tweaking the inlet manifold.

Do not get me wrong.  I am totally in favour of well designed and proven equal distribution inlet manifolds.  It is just that 99.9% of people who design their own have no idea how to make the flow spread evenly, and no idea how to fix a poor design if they bother to test it and find out that it sucks.  Internal aero treatments are a black art.  It is quite likely that the Greddy, HKS etc plenums are not even that well designed.  I haven't looked at what results people get from them (in the way of correct mixtures as shown by per cylinder exhaust temps), but it's a fair bet that they're really just designed to look good and be as big as can fit in the space available.

Edited December 1, 2011 by GTSBoy

[Bsa]

I'll run the stock tb and see what happens. Just did the calculations and plenum will be 4.9 in volume which is more then big enough. I totally understand what you saying gtsboy I'm not trying to achieve a mirical if I can get results like the plasma man I'll be happy

[wolverine]

I say go for it.

[Bsa]

Thanks mate

[GTR_JOEY]

Yep do it, if u fail who gives a fu$k,

I sure as hell aren't going to pay you out for having a go

Keep us updated

[Jeremy93]

Just do it man, no one knows how long the plazma man plenums etc took to design and get right, all it takes it one person to change a car scene, you might be that one person who can make cheap reliable and proven manifolds, but only time can tell.

Will favourite this thread, I say pics

[Tony de Wonderful]

So is runner length and width pointless on Forced induction? I didn't know that?

What about off boost torque? It's good to have low down torque I reckon off boost.

For my R33 on the street I have the OEM turbo at 0.85 bar. It works really well as a responsive street car because I get full boost and a flat torque curve from just under 3k to just slightly dropping off at red line.

So for street speeds. i.e doing 2nd gear pulls it is full of win, really snaps the necks of passengers from the bottom of the rev range.

[Bsa]

Runners are a major factor and plenum size for that matter. You can't just bolt any plenum on and expect it to work cos you have a good turbo setup everything has to work together. For a stock setup I'm sure you can't beat the stock plenum 1000s of hours went into designing it. When you start changing turbos and exhaust manifolds induction will change so a bigger plenum will benefit your setup if you can get more air in your engine will love you for it

[blk94r33]

But really, we're talking about turbo engines here. The turbo is far more important. Making the boost threshold as low as possible by correct exhaust manifold design and turbo selection is far far more important and effective than tweaking the inlet manifold.

+1

Stock exhaust manifold, stock R34 turbo, DE+T R33 here, and other mods yield a boost threshold of ~1500rpm. 7psi by 2000-2250rpm. Not a power house, but having bulk bottom-end that pulls through to red-line is awesome fun on the street.

So 3000-6500 is where it's at....

[ARTZ]

lols @ the hero who chose 5000 to 8500 rpm

[Tony de Wonderful]

Thread should be peak torque not peak power BTW.

[Bsa]

Even the stock exhaust manifold can see improvements. Iv modified one with great results allowing it to flow better by adding a external gate. People where not jumping up and down saying it can't be done more intrigued to see results. This is the same sort of thing just on the cold side

[R31Nismoid]

RE: initial question, you are talking RB25 so 5000-8500rpm is out of the question for a stocker

Only two choices, and those two choices will depend on turbo selection over and above anything else.

It's funny you see people save $700 on a turbo/manifold, so they can spend $700 on a plenum.

Spending the money on the turbo/manifold will always reap better benefits as its the most critical part of the setup on a FI application as the low-mid level modification marker. Only once you start making serious beef do things like head work and so on come into the equation, and that is simply to the the substancially larger budget.

Not saying this is a bad idea, i say go for it, especially if you've got the tools to make it economically (of course the time as well).

*BUT* if it means you are going cheaper on turbo selection to fund it, that is going backwards.

Tell me how many tests have been done on a 300 dollar eBay special fck all it works so people buy it.

Remember they are generally a copy of someone else who's already done it

Or so similar there really isn't anything in it design "difference" wise.

[NoFigJamHere]

Mate i agree with your comment re:they dont get what your trying to do! And not saying people in here aren't really qualified to answer the questions your asking but i wouldn't take to much of it in. Just by saying its Made in OZ will get you attention due to the majority of Chinese made crap knock off's. I suggest you take a good look at an OEM RB26 intake manifold, there's something inside those a good eye can spot thats really quite trick,and theyre very good. ;-) as for power range/band the engine specs/mods and tuning will control 95% of that. Trumpets for each cylinder (if u can do and keep witin your desired budget) will help off boost response. I like the fact your having a go mate and good luck.

[Bsa]

Thanks mate good to see not everyone condems new ideas

[GTSBoy]

If it was a new idea......

[Bsa]

What is your problem mate seriously? Did you fail to do it yourself so now no one else can have a go like seriously I'm done trying to convince you that this could work. Take your issues else where

[GTSBoy]

I don't think you understand what I'm saying. In reverse order (ie, taking the most recent issue first);

Point 1: It's not a new idea. Of course it's not a new idea. It's been done to death. There are all those expensive Jap ones. There are the cheap Chinese copies of the Jap ones. There are kits to put the RB26 plenum onto cut down RB2X runners. There's the Plazmaman plenum to put on the top of the lower half of the original. The list goes on.

Point 2: Not one of these options offers a significant difference in power really. The Greddy style ones hurt the bottom end for a slight improvement in the top end. The Plazmaman ones seem fairly neutral, although it doesn't seem wise to me to try to use the bottom half of the runners into a front entry plenum unless you spend a lot of time doing flow treatments* inside the plenum to make sure the distribution is good. This is because the bottom half of the original manifold was designed to work with the top half, which anyone who looks at an RB manifold should be able to work out is a pretty strange looking thing that looks like it shouldn't flow evenly but does. This indicates that the Nissan guys spent some time and effort making it work that way, because they certainly wouldn't cross their fingers and hope like most home plenum fabricators do. The only reason these plenums are worth having is that they allow you to put the bigger TBs on that are needed at higher power levels, make the pipework easier and shorter, and probably have bigger diameter runners to try to make them less restrictive at high power levels. There is really nothing else in it.

Point 3: At no time in this thread did I poo poo your idea to build a plenum yourself. I didn't even say anything to warn you about how hard it is to get right. I didn't even say that for the time and effort involved you would be better off to use a proven one because you are unlikely to do a better job and the proven ones won't need to be sawn open and fiddled with after the first build to start fixing the flow balance problems (assuming you know how to test for even flow and do so instead of just bolting it on and messing up the mixtures). I let other people say these very true things. What I did tell you is that you were wrong in thinking that you could have a significant influence on peak torque or power revs. You are most certainly free to make your own plenum. I didn't say you couldn't.

You either need to learn to read, or think, or both.

*If you don't know what I mean by flow treatments, then good luck getting the plenum to flow evenly.

[Bsa]

I'm trying to Design a plenum that is cost effective that give people the option of using stock parts so on. Without damaging flow and response. Also not spending 1000s of dollars to buy a jap one. I understand how they flow I also understand the runners are the main part that makes it work but not everyone wants balls out power most people are happy with a tidy looking bay and a nice responsive set up. Are you now going to bring me down for building a fuel rail saying I don't understand how it works. I'm not some young punk that thinks he can do whatever I'm actually putting mathamatics and science into designing it all. Tell me have you ever stepped out of the box and tried something for yourself rather then being like a sheep and doing what people say is best. Do you do or your own your or pay a mechanic to do it? You have said what you needed to say and I understand your views. But please keep your input out now rather then stirring up a argument. Oh there is a thread in the fab section regarding a external gate on a rb20 manifold y dont you go and tell me how to improve on that seeming your the expert

[GTSBoy]

If you only knew. If you only knew.