Inlet plenum design

[zetecspit]

I have been pondering inlet plenum dsign for single throttle body EFI.

Very likely I am overthinking things, but rather than a simople log or rectangular box, what about a dual plenum? I found this bit of work

https://www.goengineer.com/blog/manifold-optimization-with-solidworks-flow-simulation-part-1

This has made me think, is it better to have a dual plenum, with the joining area having a long slot so air is more evently distributed over the length?

Ideas/views more than welcome!

[JohnD]

The paper you linked to is fascinating! Wish I had that software!    But did you notice the retrograde flow predicted (Pic.8) at the furthest intake bore?   Not good!

And, the objective of an intake plenum, IMHO, should be for it to be as big as possible, so that air slows down in the large volume and raises its dynamic pressure for better inflow.

To that end, the 3" diameter plenum for Pi is too narrow.   Some have found evidence that the far cylinders go rich from inadequate air.   I simply made the plenum twice as big, 6", which is as much as I dare in the Vitesse,as it scrapes on the wheel arch.  Resistance to flow varies as the Fourth Power of the radius, so double the radius, flow goes up SIXTEEN times! (2×2×2×2).

If you feel very ambitious, another inlet mod that works is to have variable length inlet ducts!    Just as resonance can improve exhaust extraction,  so it can intake.    The heat of the exhaust primaries makes variable primary length  difficult, but "trombone" inlets have been done, to extend the effect right across the rev range.    Search on Google for 'variable length inlet' for lots of papers.

John

[zetecspit]

22 minutes ago, JohnD said:

The paper you linked to is fascinating! Wish I had that software!    But did you notice the retrograde flow predicted (Pic.8) at the furthest intake bore?   Not good!

And, the objective of an intake plenum, IMHO, should be for it to be as big as possible, so that air slows down in the large volume and raises its dynamic pressure for better inflow.

To that end, the 3" diameter plenum for Pi is too narrow.   Some have found evidence that the far cylinders go rich from inadequate air.   I simply made the plenum twice as big, 6", which is as much as I dare in the Vitesse,as it scrapes on the wheel arch.  Resistance to flow varies as the Fourth Power of the radius, so double the radius, flow goes up SIXTEEN times! (2×2×2×2).

If you feel very ambitious, another inlet mod that works is to have variable length inlet ducts!    Just as resonance can improve exhaust extraction,  so it can intake.    The heat of the exhaust primaries makes variable primary length  difficult, but "trombone" inlets have been done, to extend the effect right across the rev range.    Search on Google for 'variable length inlet' for lots of papers.

John

It seems difficult to find definitive answers to stuff. Your PI plenum has the butterflys after it, wheras I want a single butterfly on the intake to the plenum. I believe the requirements re volume are very different, too big for me will loose throttle response.

The cylinders in teh animation get the most even airflow, which is important. Unless I fit a wideband to each cylinder and tweak each injector, which sounds complicated and well above what I aim to achieve.

 

Re variable intakes, teh ST170 my engine came from has those on teh std car. It has a stepper motor to move them, all contrlled by teh ECU. But again, beyond the scope of my project.

 

[JohnD]

Steal more from the donor car?!?

Your point about throttle before or after the plenum is most valid!   Id love to know more - can you lonk to anything that would educate me, please?

John

[zetecspit]

Have yoiu seen the compexity of "modern" car intakes. Saying that the ST170 is over 20 years old. Twice as old as my first spitfire!

I intend to use the KISS principle. It can work almost as well as the far more complex OEM stuff. I am not after the very lowest emissions, not the very maximum power. More very good torque. (power over 7000rpm is almost pointless, but a dollop of mid range torque is magic)

 

Edited October 1 by zetecspit