After spending a fair amount of time polishing the exterior of the intake manifold, I thought I might spend a little time on the runners. The ports didnâ€™t match the gasket real well when I started but using some abrasive rolls in the die grinder, I was able to relieve the passages to match the lines scribed in magic marker. The new manifold passages are closer to the gasket shape and location, which is a good match to the passages on the cylinder heads.
The friend who did the machine work on my engine back in the early 80s gave me an aluminum Edelbrock Streetmaster 2.0 manifold (it was off a work truck). At the time I thought it was going to be an improvement over the stock low-rise cast iron manifold and it would fit under the stock hood. This manifold was designed to produce low-end torque and to improve gas mileage, which was an issue back in the late 70s just like it is now. When I pulled the old intake off, I discovered a clue to the wimpy performance of this big block. Talk about mismatched runners. The oil splashguard must have been designed to keep the plenum cool (along with the heat passage blocking plates. Not sure if cool gas offsets the loss of a quarter of the runner cross-section.
The new Summit manifold on the left is more than 2 inches higher than the old Edelbrock. Thatâ€™s just about how much extra height the L-88 hood gives me so it shouldnâ€™t be too much of a clearance problem (yeah, right).