Plenum volume?

[Walter R. Malik]

If your manifold's too big for your heads just bolt it on, tapering the heads port entry could kill it.

Witnessed that phenomena happening, many times.

[hoffman900]

If you have seen the animation of the fluid motion of the plenum in a tunnel-ram, you will know that the pulses are quite local to each port.
That is part of why shape matters.
You can add all you want to the end of a tunnel ram plenum, it means very little to the other end.
Even on a singe plane, it is far too complex to define by a volume dimension.
The way a pulse reflects off the walls of a box is very different than how it reflects in a sphere.

I think plenum volume is one of those things that became a dimension to measure and discuss, because it is an easy dimension to measure, more so than because it is the most important.
The frequently used formula for plenum resonance don't relate well to common plenum shapes.

Roush Yates / Converge cfd sectional view of a carburetor and plenum:

https://www.facebook.com/RoushYates/vid ... 7S9Ucbxw6v

Obviously this is slowed down greatly vs reality and the pressure waves are in a constant flux (because rpm isn’t static).

[David Redszus]

I used a log plenum as an example because that is the shape used on the
BMW engines that I have tuned for fifty years. I tried to show that plenum
volume may not be an adequate indicator of performance improvement.

A box shaped plenum would produce waves of various frequencies and
amplitudes that I am not able to predict.

That said, any attempt to predict performance without considering the
total induction system, will probably result in dubious results.

[SchmidtMotorWorks]

Roush Yates / Converge cfd sectional view of a carburetor and plenum:

https://www.facebook.com/RoushYates/vid ... 7S9Ucbxw6v

Obviously this is slowed down greatly vs reality and the pressure waves are in a constant flux (because rpm isn’t static).

That converge software looks very interesting, I have been meaning to learn more about it.

[hoffman900]

Roush Yates / Converge cfd sectional view of a carburetor and plenum:

https://www.facebook.com/RoushYates/vid ... 7S9Ucbxw6v

Obviously this is slowed down greatly vs reality and the pressure waves are in a constant flux (because rpm isn’t static).

That converge software looks very interesting, I have been meaning to learn more about it.

https://youtu.be/ZHTSQWwrmjU

Check out the full exhaust stroke at the 1:00 mark (and play at 1/4 speed). I believe Brian Kurn is now doing his own thing, might be worth reaching out to him on Linkedin. He was there CFD guy and has a really interesting background (RY, ECR, Hendrick, Barton, Reher Morrison, etc).

[SchmidtMotorWorks]

https://youtu.be/ZHTSQWwrmjU

Check out the full exhaust stroke at the 1:00 mark (and play at 1/4 speed). I believe Brian Kurn is now doing his own thing, might be worth reaching out to him on Linkedin. He was there CFD guy and has a really interesting background (RY, ECR, Hendrick, Barton, Reher Morrison, etc).

Thanks for the tip.
I have a couple contacts at Converge, I'll ask if they will support some of the demos I do here.

[BLSTIC]

Roush Yates / Converge cfd sectional view of a carburetor and plenum:

https://www.facebook.com/RoushYates/vid ... 7S9Ucbxw6v

Obviously this is slowed down greatly vs reality and the pressure waves are in a constant flux (because rpm isn’t static).

That converge software looks very interesting, I have been meaning to learn more about it.

https://youtu.be/ZHTSQWwrmjU

Check out the full exhaust stroke at the 1:00 mark (and play at 1/4 speed). I believe Brian Kurn is now doing his own thing, might be worth reaching out to him on Linkedin. He was there CFD guy and has a really interesting background (RY, ECR, Hendrick, Barton, Reher Morrison, etc).

exhaustflow.jpg

And that right there is likely why Calvin/exhausted preaches smaller pipes off the head, and hasn't had issues with large reductions in size at the header flange. Even in this near perfect curve the inside is under-ultilised. And if that change in diameter near the blue spot is evidence of the header flange it's basically pointless having a pipe there at this particular part of the stroke.

[1980RS]

I know in my testing the Vic Jr. I used had a pretty big plenum and the car was slower with it on the car. Same thing happened with my BBC peanut port engine, ran the Dart oval port intake and the car was a dog. Put on the old Team G intake I had and that engine was a lot happier with the smaller plenum.