I only have one question for now. What the hell do you do with the stock primary injector ports or are they still used along with the 4 injectors on the new setup?

if you want better driveability use the stock primary spots. mazdas got some graphs, they used the stock primary location on the 787, where fuel efficency was important. the higher location gives 1-2% more power, but it takes more fuel and driveability is worse

*sigh* No, wrong answer.



A well designed plenum-style intake manifold is actually capable of outflowing any ITB setup. Period. Through harmonic tuning, you can get a lot more energy to help force air into the ports than with an ITB and you can do it over a much broader set of RPMs. The plenum and whatnot helps recover a lot of the little shockwaves bouncing around, and there's no real reason it would have any more flow restrictions than ITBs aside from lousy design.



The reason ITBs are used on race cars is pretty simple; throttle response. There's very little volume between the throttle body and port, so that when a change in throttle position is made, the engine responds almost instantly because there's less air mass and thus less inertia. Oh, and they're also easier to fabricate and package. Of course, these advantages sort of disappear with forced induction cars; with a turbo, you have to wait for the air mass in front of the throttle plate to catch up, so the air mass between the throttle and port isn't much of a concern. Another downside is that throttle control is a bit more edgy; below something like half throttle the ITBs will flow quite a bit less than a single butterfly for a given throttle position but they suddenly start catching up closer to WOT. To put it another way, a lot less control over part-throttle, which is where most people spend their time driving.



That said, ITBs *are* easier to fabricate and sometimes off-the-shelf intake manifolds are just completely unsuited for an application. It's dead simple to make velocity stacks coming out the side of an engine, but a well designed plenum manifold takes a bit more thought... sometimes more than the manufacturers can manage. https://www.nopistons.com/forums/pub...#>/biggrin.png

Wow, thanks for the information. https://www.nopistons.com/forums/pub...IR#>/bigok.gif



That was just my guess, obviously, because I don't know anything about this kind of stuff.



So who makes intake plenums for 13bs?

Heh, sure... gotta learn sometime, or something like that. I get bored between classes and write stuff, so... pardon the verbosity. https://www.nopistons.com/forums/pub...#>/biggrin.png



As for who *makes* plenum style manifolds... well, that's an interesting question. I don't know that anyone really does off the shelf. I mean, you can get them built, but...



Everything I've heard though says that the Cosmo 13B has about the best intake manifold Mazda stuck on a factory car (except maybe the RX-8 one) so personally I'd just be looking at options for a bigger throttle body on it.

What about using these ITB "kits" on na's?

Not sure where you are coming from on the apples to apples comparison here. If you take 2 setups, both with optimally tapered runners terminating in a volume with decent bellmouths to get a good reflection, but one has butterflies in each runner and one has a single butterfly in exit of said volume, then as far as the air is concerned you have identical systems and both will flow the same.



If you are saying that plenum is short runners and the main resonance being due to the airbox/inlet tuned system vs a long runner IR setup, then the IR setup will flow way more, simply because the reflection pulses off a closed exhaust valve have a far higher intertial supercharging ability than a helmholtz resonance due to a plenum. However the length of that runner is critical and in most cases is way too short to get the main reflection coming in at a useful time.

damn that guy has a lot of money for his age

Excellent.



Thanks for the info. Although I don't have the motor yet, I'm already thinking about stuff to do to it. https://www.nopistons.com/forums/pub...IR#>/bigok.gif

Well, on NA motors they make some sense... and you could make the argument that they will flow more because the stock manifolds are crappy. I won't say whether that's true or not because it depends on powerband the engine's tuned for, and I don't really have numbers anyway. I personally am building an IR manifold for the motor that's in progress, probably fed by a Weber IDA. It's going on a peripheral ported engine though, so... https://www.nopistons.com/forums/pub...#>/biggrin.png





Well, the specific apples to apples thing I was looking at were some Honda tuners. Another one to look at is what kind of manifolds various drag racing classes are building; sheetmetal "tunnel ram" manifolds being the norm. I know there's others out there but I can't point at them quickly; I apologize for this being briefer than I'd like, but I have studying I have to do.



Taking two setups like you said, you're right they are about equivalent. There's small differences because of how much port area is being taken up by throttle shafts and butterflies, but we'll ignore that. https://www.nopistons.com/forums/pub...DIR#>/wink.png



You were pretty much hitting it comparing a short runner plenum setup to a long-runner IR setup. If you can *make* an IR setup with long enough runners it will flow the same (at reasonable RPMs) The trick is, to do that the runners start getting impracticially long. You're getting the 2nd and 3rd order harmonics to help out, but 1st order harmonics aren't doing anything unless you're running Formula 1 RPMs... quick and dirty calculations suggest a pipe length of around 800mm to get 1st order harmonics to be useful at 8k RPM. With the plenum you can tune it to get those lower order harmonics and still package it.



This is off the top of my head; specifics might be off. An interesting note though is something I saw at the SAE World Congress; Opel had one of their V8 touring car race motors there. It was using 1 throttle body per cylinder *AND* a plenum for each bank of 4. Best of both worlds?