Intake aerodynamics 1

[futteen]

Have a dual plane intake which i have some thoughts about the designs of intake how it can maybe be improved, I know a 90 degree /single plane intake would better but not that easy to come by for this engine i was wondering if i fill in epoxy in certain areas to smooth out the entrance to the runners or just file some on the narrow section

http://smg.photobucket.com/user/futten/library/my car/intake?sort=3&page=1

 

[tbuelna]

Is this manifold intended to be used with a carburetor? When using this type of intake manifold with a carburetor, even fuel/air mixture distribution between all of the cylinders is of more concern than maximizing airflow. If you want to improve the performance of this manifold by altering the runner geometries, you'll need some way to measure the effect of these modifications on distribution of the fuel/air mixture to each cylinder.

 

[futteen]

sorry shoulda said it was a turbo blow thru carb setup

 

[BrianPetersen]

The point still stands. Watch out for the wet-flow effects.

 

[futteen]

so even just adding epoxy to smooth the entrance could create problems?

 

[tbuelna]

Maybe or maybe not. As I pointed out previously, when using this type of manifold with a carburetor, the most important thing is to get a uniform A/F mixture at each cylinder under all conditions of speed and load. If your manifold produces a lean A/F mixture in a single cylinder it can result in damage from detonation.

Of course, sand cast manifolds typically have a fair amount of geometry errors. So reworking the runner surfaces to balance their flow properties by machining, or adding epoxy and hand working them, should usually improve things.

 

[140Airpower]

"...reworking the runner surfaces to balance their flow properties by machining, or adding epoxy and hand working them, should usually improve things...". Really? I think this relies on changes being small (not significant).
If the manifold is very well designed with respect to mixture distribution, you can use more boost before the leanest cylinder limits you.
I think significantly changing things should make distribution worse... unless you check mixture flow as you go along. Not easy. Ideally it would require a dyno.
Here "significantly" would mean the changes make a worthwhile difference in total airflow. But if the distribution gets worse you may have to limit boost and end up with less power. If your manifold is very good wrt distribution, IMHO it might be best to just increase the boost if you want more power.

 

[futteen]

one way of improving is i already know of is to either slot or remove the plenum devider

 

[RossABQ]

one way of improving is i already know of is to either slot or remove the plenum devider

On NA applications that is usually a bad idea for a street engine. Can't say on a blow-thru but I'd be wary.