Intake Plenum design

[Nero]

Warpspeed there are a few things that you have missed but I don't think that I have the ability to explain them very well. What happens within the plenum is very complicated with not only the changing mass of air but also with the changing pressure waves etc etc that it beyond my ability to work it out. I have not seen a computer program for the plenum design as I think that there are too many variables. Perhaps it would be best to make a variable size plenum and change it on the dyno to see what works best and then fix it at that size. Don't forget the second set of injectors pointing into the runners...shame not to try...probably has a greater effect on HP?
Prosche use cross ramming of the pressure waves as doo some other manufacturers with very good results at certain RPM. Nascar engines make more than 110bhp/lt with two valves and a carbs...at certain rpm their VE is supposed to be up to 110, which is outstanding. BUT lots of dyno time and lots of head scratching...I can afford to scratch my head (and my balls on a payday) but that about it for me!
Also look at stepped headers as the intake peformance does occur without similar tuning of the other side.

[Maadmike]

Hmmm...

Thankyou very much for the replies guys, keep emcomin! great help.

I'd be aiming at the performance car market, so i'll be designing a plenum that delivers the torque high up.

I'm also very interested in the variable plenum subject, i may look into it if there is a good enough advantage. If it was put to good application, and i had access to a dyno, a plenum could be designed with valves etc to give a flatter torque curve, kinda like variable valve timing, but this time around it could be 'variable Plenum size'. Like i said in theory i could be intersting to find out what advantages could be had, and if they are worthwhile?

My main aim atm is to get a look at designs of different plenums in high performance engiens and work from there, and, if it proves that it may be worth while i might just experiment with this variable plenum size thing...

[Warpspeed]

As Nero says thre are a few things I left out concerning plenum design.

The actual size (volume) is only going to have a weak effect at the resonance point with the runner volume, so it is probably not worth bothering with trying to tune it to a particular RPM.

I have never tried it, but these days there is fairly cheap software available to design bass reflex loudspeaker boxes. Maybe you can enter plenum volume as box volume, and runner diameter and length as port tuning parameters. You might be able to extract some meaningful numbers, I really do not know, just another nutty idea perhaps?

The main plenum function will be to distribute air evenly between the runners, and it is here that a large plenum will help because the velocity inside the plenum will be lower.

Also the plenum to runner junction is absolutely critical, there MUST be a good smooth bellmouth shape.

Injector location is a completely different subject as is valve timing, but both must be part of the overall development package as well.

This must also work in harmony with exhaust tuning, which is another subject altogether.

[Ben Wilson]

Unfortunately, speaker design software won't work, you need a lot of specific parameters for the speaker before you can go anywhere.

Take a look at winISD for some excellent freeware speaker design software if you're interested.

[Warpspeed]

True Ben, if you were designing a speaker box you would need all the Theil and Small motional parameters for the particular driver and enter these into the program. You the tune the port to 0.707 of the modified cone resonant frequency as mounted in the intended box.

But you could possibly fudge the numbers, and reverse engineer the whole thing to work out what port resonant frequency would result with given plenum and runner dimensions.

I have never used the modern software myself, but many years ago built several bass reflex boxes based on the original thesis of Theil and Small. The original research work carried out at Sydney Uni is now famous, and should be available on the net somewhere.

Another way if mathematics is your thing, look up Helmholtz Resonators, or Helmholtz Resonance on the internet. It will explain the principles.

http://www.phys.unsw.edu.au/~jw/Helmholtz.html