Intake Plenum

[jcisworthy]

Factory dual plane intake for the fast series , sharp edges at the transition to the runner below the carb mounting

Anyone ever test on any intake to see if a sharp edge at the transition makes more power over a blended edge?

I was thinking the sharp edge could act as a fuel shear but the porter in me wants to shape and blend them

[Erland Cox]

Sharp edges should give you a vena contracta making the air believe that the area is smaller than it is.
Sharp edges kan be good on valve seats to help air turn but not on the entrance.
You don't need much radius though except for in the roof.

Erland

[jcisworthy]

Thanks Erland

[mag2555]

The air speed in the plenum is not FAST enough if the carb is BIG enough to feed the level of Hp looking to be made and in fact a bit more.

I have always found that duel plane intakes and a motors power band is never harmed by running a carb even 60 cfm bigger then the old standard that we have heard for decades.

You may need with the bigger carb to use one fitted with high gain boosters to still meter low speed fuel as needed.

Leave it to act as a fuel sheer point should it be doing such.

What helps the most in a fuel plane intake manifold especially for the upper plenum is to add a spacer .
This will give the air mass more room to make that turn plus not jerk and bend around the air mass coming out of the bottom of the carb Venturi that feeds that plenum

[jcisworthy]

Carb spacers are not allowed and it may be a 600 CFM on a 431 CID. Trying to get a 750 approval but may not happen

[1972ho]

The way you can possibly get around that spacer rule is to get yourself a couple of those 1/4 inch gaskets and glue them together.https://teamc.com/images/F145485905.jpg

[Carnut1]

You don't need fuel shear you need as much flow as possible with that carb and intake. I always make as big a radius as possible into plenum. If you mount the manifold upside down on the bench and fill the unused ports with foam from a pillow packed very tight you can flow each runner in exhaust mode. I did a video on it a while ago. Plenum work pays nice dividends.

[jcisworthy]

Thanks

I'm only porting the intake. I believe he can run only one 1/4" gasket.

The engine is an AMC 390. Anything is allowed on the inside. He has a 3.9" stroke crank he wants to use and 4.195 bore

He said there is a possibility they will allow a 750 Edelbrock carb but no answer on that yet. I believe he has an AFB carb now