Wed Jan 15, 2014 9:25 am by gt1cooper
I understand completely why you might not include it, it is a minor thing, but it can be a thing that will actually have an effect. High-performance, or high-rise, intake manifolds have wider, longer intake manifold ports with a higher vertical rise, all of which combine to increase fuel flow and fuel speed into a vehicle's engine, which in turn increases engine horsepower and performance. The greater amount of fuel, the lower the RON as you know, so that is how that effects the RON. Higher rise manifolds help mostly at higher rpm, when more fuel is being dumped in, while at low rpm, fuel molecules are not really obstructed by their predecessors. A higher valve lift will allow much more fuel into the combustion chamber when coupled with this. That is why, on my Mustang with it's 427 stroker, I had to pick between a low, mid, or high rise engine. I do not have the power charts available, but I picked mid rise for two reasons. One was because with the mid rise, a functional 2 inch hood scoop would fit the air filter for the dual 850 holleys, and the other was that with that intake, I had a flat torque band from 3000 rpm to 5700 rpm. The low rise intake's torque peaked at 4000 and dropped off at 5000, and the high rise had the same mid range power of the mid rise, plus an increase where the torque curve held steady to 6500 rpm, and did not fall off all the way to the limiter of 7750 rpm. However, the air filter would have stuck clean out of the hood, and I did not want to deal with the fabrication, forward visibility, and price of having such a setup. Resonance does also have an effect, and I understand the nightmare that is valve timing for the static Helmholtz resonance property of the air vs. the dynamic timing. Just, on carbureted engines, this is one of the many ridiculous things that, when you are building an engine for a car, must be considered. (It was a nightmare, trust me. I used to work for FoMoCo as an engineer and team manager focusing on the top end, from intake to valves.)