Some M1 porting pictures and flow numbers

Should horsepower potential be based on flow with the intake instead of heads alone?
You can guesstimate HP based on cylinder head flow. The old layman’s way is cfm X 2 = approximate HP for a good street strip engine. It’s a basic formula that is not accurate but ball parks potentially what can be done.

The trick is using an intake that will allow the head to flow its maximum.

If you have a set of heads like what John ports these aluminum heads to, let’s round it at 300 cfm. It has the potential of 600hp.
It’s not getting there with a cast iron TQ intake. With the OOTB M1 bolted to the ported heads, he came up with 271 cfm @ .650 lift. This has the potential of 542 hp.

Can more power be made? Yes.
If all becomes how and what the combo is consisting of.

To reach 542 hp on a 360, it will need a reasonably sizable camshaft and compression to back it up with a good exhaust. Etc, etc, etc…..