I've been posted this tread in difference places hoping to get answers that could help me... To make a long story short. This winter I change from Mopar M1 dual plane intake mainifold to the manifold that all recommended for my mild 383 .030 over, decked block, Lunati 256/262 @050 213/220, Speed Pro flat top pistons @about 0.0 in the hole, 915 heads, 650 AVS2 and Mopar HP exhaust manifold with wideband AFR meetering about 40" from the closest exhaust valve. All recommendations where the Edelbrock RPM intake manifold. So far so good. With the M1 IM it ran pretty good and AFR was very satified, about 14@cruise and 12-13@WOT. With the RPM I need to rod and jet up quite a bit to get a decent AFR@cruise. Well, so far so good. But then I floor it (and all of the information below is when I floor it), a major bog and totaly lean out then reading 16-17 AFR@WOT I was running .098 as main jet with M1. As it was way to lean my first step was to jet up to .104, not much difference in AFR. I then tighten the AVS one full turn, not much difference. I then jet up to .110, still not much difference in AFR, first bog then about 14 AFR area but stil too lean. Is there really that much difference in flow between the RPM IM and a "standard" dual plane IM?