When the Eddys first came out, I bought a set for my 500" stroker project. At the time, I had a very worn 440 in the Cuda that only had a cam, intake/carb swap and headers. At the end of the driving season, I decided to throw the Eddys on the engine just to see what they would do. Some said that the car would actually slow down due to the low compression. To be honest, I don't know what the ratio was.

Anyway, with no other changes, from one weekend to the next, the car picked up nearly a full 2 tenths with just the head swap. That was obviously due to the better flow of the Eddys over the stock iron heads, but if the aluminum hurt anything in this case, it was not much nor noticeable.

Just my experience.