making a 4 hole intake into a dual plane type

[olman]

I have a C7AE-9425-E intake and was wondering if there were any benefits of making it a dual port style base. I did this to a 292 y-block manifold on a well prepped engine and was pleased with the results. I went down in the port runners and ground out a lot of the sharp turns and restrictions to make it flow better. Later on I put on a Blue Thunder intake and REALLY woke it up.  If anyone has done this, is it worth the effort or should I just buy an Edelbrock Performer manifold? This is on a cammed up '67 428 with some head work on the C7AE-A heads. Also running cast long tube headers. Thanks from the ol man.

[Drew Pojedinec]

Should be simple, it's already a dual plane intake.

[jayb]

You are talking about changing the top of the intake so that instead of having four holes, it has two long oblong holes, like a police interceptor intake, right?  I know a guy who did that with a Cobra Jet intake, and it worked out pretty well for him.  He was able to get in there and port in the plenum areas, and then combined with some porting in the runners he picked up about 15 horsepower on the dyno, over a stock cast iron intake.  One thing I would say is that the four hole top on the manifold actually adds to the vacuum signal that the carb boosters see, so if you do this, you might want to run a 1/2" 4 hole spacer under the carb, to avoid losing that vacuum signal.  May or may not be necessary, but it couldn't hurt...