My truck had been sitting for 10 years, had way too big a cam in it, had 7.7:1 compression and the 1970 manifold. I had the heads milled 0.080", ported the heads, changed the cam to a much smaller cam and installed the Air Gap with a 650 AVS2 all at the same time. It does run much better but still needs some tuning. I can't tell you how much difference the Air Gap made, but by looking and running my fingers through the manifolds I know it's a good bit better than the factory one.