Originally Posted by dpjmw
I ordred a summit brand intake manifold for my street rod build. I notice that the intake runner openings that match up to the intake runners on the heads are not square with each other and they are a little smaller than those on the heads.
Is this a big deal ? or ? is that how they make them?
Unless you're a competitive racer needing every conceivable horsepower, this is fine. It's better to have the manifold a bit smaller than the ports such that the port never presents a 90 degree wall to the oncoming flow. The other direction where the manifold walls present a 90 degree surface to any reversion flow coming back up the port is beneficial to reducing this reverse pumping into the plenum and backward thru the carb where it causes stand-off.