Plenum Theorum

[Paradoxx]

Hehe nice! I think mine was the std 16G turbo, but I had RX7 injectors, EVO cooler and no cat... came second at an RPW drag wars one year. I had that thing up to about 22psi without going lean.

[Nizpro]

This could turn into a long post as this subject has a Hugh amount of variables. Firstly there are two ways that people can go. One is to make the plenum monstrous this is to simulate no plenum at all. By doing this you will be trying to make the inlet think its N/A. F1 style. In a perfect world if the engine bay was big enough and the engine was to be kept at a constant designed engine speed this would make the best outright power. Guess what this is not the real world, so by the time you facture in throttle response, idle quality and the fact you need to fit the thing in the engine bay that pretty well rules out the monster plenum

Now inlet runner length is very important and needs to be matched to the desired rpm range that you would like the engine to work best in. For best power you try and match the desired rpm with the primary pulse of the inlet runner. As this will have the strongest effect as the pulse in also the strongest. So on a standard Barra 6 the lower half is of the intake manifold is around 12 inches long our plenum adds around 1.5 inches to this making a total of 13.5 and finally the intake port itself. In theory this length will give us the great influence at around 6200 rpm. I believe this is around the rpm that most guys will use once hotting up there XR6T’s. Of course this gives a little leeway either side with regards to the rpm range.

You will also get a pulse at half that rpm range although it to will be half the strength of the primary pulse. Once again this gives you a fairly good result at approx.3000 rpm for good torque in the mid range.

Now this would be occurring with no plenum, the problem is that the torque curve would have a peak spike at 3000 and then again at 6000rpm.This is seen on V8 super cars and any engine with straight muti butterflies style inlet manifolds and is a bit ordinary for road cars, although peak power once again would be greater.

The intake plenum needs to be designed to try to even out the pulse’s that are occurring from the intake runners. Now once designed correctly the torque curve will be flattened out giving a more constant [although less peak] torque curve. It achieve s this by the refection of the primary pulses inside the plenum. Because of this the plenum does need to be made from a ridged material as any flex will absorb the pulses like a shock absorber. This is why we cast our manifolds and not fabricate them. This is also the reason why expensive race engine that are looking for a reduction in overall engine weight run carbon fibre plenums. In fact our new plenums for our new 6.0 quad turbo v8 race engine are carbon fibre.

Hope this helps a little and besides my lunch break is over and people are yelling at me

[Guest]

I read this and laugh

the fact that people quote this theory and that theory tells me they dont have enough brain to see logic them selves

bens coments in the first post in great part make sense as does the last sentence in driftpigs post

if turbo is involved money is better spent on other mods as plenum will only give minor gains.

preasure and airspeed is whats to be considered along with air density!!!

the old kiss theory works best

the engine is an air pump the more air you get through it the more torque you make the more torque the more power

power is torque x speed so you want max torque all the time

to aheive this you need max air flow (oxygen content)

to acheive max airflow you need ideal air speed & density

and finally once you have calculated the ideal airspeed for your engine combo then you can find the volume of your plenum and so the vicious circle starts

ill bet 100% of plenums and manifolds are way of your own particular needs its not some thing you can get right mass produced

saying this re read this

if turbo is involved money is better spent on other mods as plenum will only give minor gains.

[Guest]

In fact our new plenums for our new 6.0 quad turbo v8 race engine are carbon fibre.

←

Any info on this setup, what engine/car/class is it racing in and what sort of power is it making.

[Nizpro]

We are however only talking about one vehicle type here with a common opperating range,of up to about 6500rpm. Diameter of pipe dose not effect pipe lenght. Boost pressure, air-temp to a degree do, the theory dose not work out exactly but it dose give a close idea of a good starting point. Without knowing how to work this out you will spent lots of extra time doing R&D.

Of course a different or bigger turbo will make bigger top end gains than a new inlet, or a badly designed one. So if a dyno queen is what you are after dont touch the std one just pile in the boost. On the other hand if you want a nice responsive engine that uses less fuel and makes the same power on less boost and all the gains that come along with it, then inlet,exhaust manifolding will help.

Ben I believe this is a good topic and one that should continue,it is one that I'm am still learning about every day.Blazz on

[Nizpro]

Our new engine development project is a 6.0 liter quad turbo 32 valve V8.It develops 1 megawatt and has been designed for off shore and ski racing boats.We give it a full warrenty for 25 racing hours. Not quite sure if this fits this post. There is more info on it if you are interested in our newsletter and forum.

[Guest]

Ben I believe this is a good topic and one that should continue,it is one that I'm am still learning about every day.Blazz on

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I agree we all learn every day

[F6 UTE]

Thanks for the informative posts gentlemen..

I obviously, as I have mentioned have only theories, and other peoples/companies work to go on. Wog knows this, as I ring him with a brilliant idea, explain it, then say to him " Tell me why I'm wrong" and he does.. him or gramps.. They both bring my ideas back to earth with simple logic..

Simon G/Wog, how far from 'perfect' can a plenum be before it is a complete waste of time?? Would you expect similar results with a plenum like Rob - 'Mr Turbos' in conjunction with your stage II for example?

I'll have a go at this plenum and see what happens, if it's waaay wrong, I'll start another one, I have a few design floating around in my head.. It's enjoyable creating something, and working through problems.. Bit like fishing, It doesn't really matter if you don't catch anything, it's the experience as a whole..

I know I could go and buy 'x' plenum and be done with it, but my mind, and personallity don't work like that..

Edited 06/09/06 06:51 AM by F6 UTE

[Xtreme F6]

argh, This is some of the stuff ive learnt over the years. Before I started doing the tuning on these cars I was heavily involved in drag racing vehicles and some of the fastest cars in the country, My Old Boss and still one of my closest friends Is a Guy by the name of Greg Gower, for those who dont know who he is he was the first person to put an alky funny car into the 5's and is one of the smartest people you could possibley meet when it comes to engine design and performance.

Greg and I worked together in a company doing Cylinder head design and manifold's ect.

We had alot of engine simulation software at our desposil and had a very large volume of different vehicles and combos to do heads ect for.

We have talked about this very subject many times, Greg still is head crew chief for Kapiris racing on his door slammer and has a very good knowledge on forced engines and is someones whos advice I listen to , as is Simon G from Nizpro.

Firstly we had talked about runner length and design on a forced engine and came to the conclusion that once the car is on boost it wouldnt have alot of effect on the engine as the pulses wouldnt be strong enough to over come the boost pressure anyways.

secondly, Obviously the more plenum volume you have the more area you have to fill, the more lag.

You have to be sure the turbo has enough supply to feed it so it doesnt loose boost, you have to make sure the exhaust can dispel the gases away quick enough, you have to make sure the intercooler doesnt restrict the flow of air to much whilst still being able to cool the heated air enough, if you have these 3 right, your already most of the way there, Nizpros plenum works well for a few reasons, volume isnt to big, it bolts straight on and at no point would it be a restriction to the engine, Not to say the runners wouldnt be, they arent the best and nicest design but for what level we are at they do the job well.

There are always a couple of things that will make things "Better" from an air flow point of view, Never have square edges, always have radious's and try and keep the volume under control.

Runner lengths, well if you have a small cube motor with no natural torque off boost then the shorter the runner the worse it will feel off boost. If you have to long a runner the more volume you have to fill the longer it will take to come on boost so again you will have lag, Luckily we have a big engine so it has some natural torque anyways.

Edited 06/09/06 07:56 AM by Xtreme F6

[Xtreme F6]

I read this and laugh

the fact that people quote this theory and that theory tells me they dont have enough brain to see logic them selves

bens coments in the first post in great part make sense as does the last sentence in driftpigs post

if turbo is involved money is better spent on other mods as plenum will only give minor gains.

preasure and airspeed is whats to be considered along with air density!!!

the old kiss theory works best

the engine is an air pump the more air you get through it the more torque you make the more torque the more power

power is torque x speed so you want max torque all the time

to aheive this you need max air flow (oxygen content)

to acheive max airflow you need ideal air speed & density

and finally once you have calculated the ideal airspeed for your engine combo then you can find the volume of your plenum and so the vicious circle starts

ill bet 100% of plenums and manifolds are way of your own particular needs its not some thing you can get right mass produced

saying this re read this

if turbo is involved money is better spent on other mods as plenum will only give minor gains.

←

Airspeed is required in the ports and past the valves, not in the plenum. Airspeed in the plenum will be a fraction of that in the ports and will be chaotic anyway. I.e. constantly changing direction, swirling and tumbling, etc.

What is ideal airspeed ? It will change with RPM, throttle opening, etc - there's no such thing except at a single RPM point. So whats ideal air speed in a street car that is constantly changing RPM?