Andy is saying it's a 25hp difference for how he tested the heads, but I feel that's probably not representative of how the heads would get used by "most" people........ Meaning, I don't foresee many builds using the 240 heads being topped by an intake manifold with what's likely over $1000 worth of labor done to it.
I'm thinking on a typical "bracket race" 505" type build, where both the 240 and 270 combo would be run with what is more the norm...... A port matched single plane...... That there would be more like 50hp difference. The 240's using something like a TF intake with a 950-ish 4150 carb, and the 270's running a 440-3 with a 1050 4500 carb.
The added power comes from not only the bigger heads, but also the bigger intake manifold.
My 50hp guesstimate makes the assumption that what the heads got put on would have enough cam, compression, exhaust to take advantage of the larger induction system.
This is exactly why this test is misleading...b/c of the high dollar, very good flowing intake manifold used on the smaller heads. The bigger heads got saddled w/ a poor flowing intake (by comparison) and the numbers suffered. Not a true A to B test so we're left making assumptions.
