Big Block Cylinder Heads "915 vs 906"

From the factory,

The #2780915 Cylinder Head {closed chamber} came though at 78.5 CC's.

The #2843906 Cylinder Head {open chamber} came though at 88.0 CC's.

If you popped on a set of #915 {closed chamber} Heads on a 1968 thru 1970
440 Engine, you would gain approximately a 'full' Compression Point.

That was with 'no' machine work.

Based upon 'general calculations', you would increase Horsepower by approximately
4% to 5% {15 to 18 Horsepower}.

In a '1968' Dick Landy article about the 'new' 440, Dick stated that the new
1968 #2843906 Cylinder Heads were designed with the 'new' Open-Chamber
"strictly to aid smog emission at lower RPM's".

The 'open-chamber' design helped cylinder flow at lower RPM's, but at maximum
RPM's there was no difference in performance with both engines running with a
10.0-1 Compression-Ratio.