Reply to "Air gap manifold"

I'd like to add 3 comments in regards to manifold design.

(1) The 351C 4V cylinder head has a ramp built into the floor of the intake port, placed there to increase air flow and therefore horsepower. The runners of the Edelbrock Performer intake manifold direct the air stream high, and thus the air stream avoids the intake port ramp as it flows into the 4V cylinder head. Edelbrock's Air Gap manifold on the other hand directs the air stream low, making full use of the ramp built into the floor of the 4V intake port.

(2) Edelbrock's Performer manifold is equipped with an exhaust heat passage, whereas Edelbrock's Air Gap manifold is not. Every 10 degrees F the air temp is lowered shall result in a 1% increase in horsepower. Blocking exhaust heat is normally worth a gain of 20 to 40 horsepower. The exhaust heat passage of any manifold can be blocked, and thus realize the gain in horsepower achieved by reducing air temperature.

(3) Edelbrock's Performer manifold has a full height plenum divider, whereas the plenum divider of Edelbrock's Air Gap manifold is significantly cut down. As fsr as I'm concerned the Air Gap manifold is a single plane manifold that "looks" like a dual plane manifold, with both the low rpm disadvantage and high rpm advantage of single plane manifolds. A person must ask themself which is more important, the peak horsepower number on a dyno sheet or the improved low rpm performance of a "true" dual plane manifold.

I consider the first two items to be advantages in favor of the Air Gap manifold, the third item I see as a disadvantage; I feel the whole reason for purchasing a dual plane manifold is for it to perform as a dual plane manifold; i.e. the time between pulses within the manifold should be doubled. I don't expect everyone to feel the same way, and I certainly mean no criticism of another's choice.

However, I would also point out that if down the road the owner of an Air Gap manifold decided they would prefer it to function as a true dual plane manifold it can be easily modified to do so, via welding a strip of aluminum plate onto the manifold's plenum divider to raise its height. An Australian company named Torque Power sells a manifold identical to the Air Gap manifold except their manifold has a full height plenum divider. This is the manifold sold by CHI to their customers wanting a dual plane manifold. The Torque Power manifold performs great ... even with its full height plenum divider.