I have one on my 440 right now, and I'm not very impressed. Like everyone has said the runners are tiny! It is probably done by 5000 RPM. Fuel injected 1968 Charger, 1976 or 78? truck/smog 440, A-833 and a Dana 60 with 3.54 gears. Averaged 11 or more MPG last year, would improve to 14 or so on the highway. I could get better mileage, if not consistently, out of another 440 with the Street Dominator. I would think my application would be good for this manifold but that's not how it's working out. Any 440, even a low compression one with a broomstick for a cam would demand and benefit from more air than this manifold can provide. I can only imagine better sorted out 440 in a motorhome would be strangled by the SP2P440. It might work okay on a 413 but not a 440. I mean a factory 4 barrel intake blows this thing out of the water torque wise.

I would use almost anything else, if this 440 makes it back onto the road, I'm definitely putting a Performer RPM on it