intake manifold ports are smaller than what's on the heads

[edmonds007]

Hi, I'm changing my intake from a Performer RPM to another one with Weber 48IDA's and when I removed the Performer manifold and looked at the one with the Webers on it I noticed that the ports on the new manifold are smaller than the ports on my heads. I would like to add that the manifold that I'm putting on the car was previously installed without any serious problems. I would like to know if anyone has any recommendations or suggestions for how I should proceed? As this is my first time really doing anything to the car myself I would welcome any advice about obtaining the best intake manifold gasket. The engine is a Roush stroker 392.

Thanks,
Bryan

[CobraEd]

Intake manifold ports that are smaller than the ports on the head help to minimize intake charge reversion.


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[LMH]

Some manifolds are designed to be ported to match different heads. Some need to be ported up and some down too, depending on application. I don't know about your specific intake but is there enough material to do some porting?
Larry

[edmonds007]

Thanks for your replies. It appears as though there is plenty of material around each manifold port. When you say "do some porting" I take it you mean that I could modify the ports on the manifold to make them a bit larger?

[Tangible Toys]

Small intake ports compared to head size is a plus, it helps to stop pulse back to the carbs and keeps the intake charge strong and dense. Also helps throttle response.

[bobcowan]

That's true, to a point. You want a small lip in the port, no more than about 1/8" or so. More than that creates a dead zone and turbulance in the port. That will cause the fuel to come out of solution and puddle on the bottom of the port. That's a bad thing.

You should make a pattern on the head ports, and transfer that to the manifold ports. SOme people just use a gasket. Cut out the port opening to match the pattern. Then work that back into the port to create a gentle transition.

Be sure to look down the carb barrels and make sure that port is big enough, too. You want a nice smooth transition there, too. But no lip.

[LMH]

Originally Posted by edmonds007

Thanks for your replies. It appears as though there is plenty of material around each manifold port. When you say "do some porting" I take it you mean that I could modify the ports on the manifold to make them a bit larger?

Basically yes. If you don't have much experience with porting, you might want to consider taking it to someone does. Not that I don't think you couldn't do it but it is kind of art to get it really right. There's a little more to it than just making the intake match the head.
Good luck!
Larry

[sllib]

I agree with Larry. I was wise enough to leave my pricey AFR heads alone but experimented on a Vic Jr. intake and overported it. Now I have a stock Vic on my engine and a expensive Edelbrock paperweight in my garage!!
Bill Stradtner