There's no queation that the Edelbrock head combustion chamber is a copy of the 915 chamber, that's a 1967. Are the ports close? I don't know, but Steve Dulcich found that the 915 head had good swirl. That, added to the ability to build squish makes the 915 pretty desirable.

IMHO the 1968 chamber was a step in the wrong direction. I believe one of the problems was the MOPAR engineer's acceptance of low precision in the manufacturing process. Even though they had the area in place, the top of the piston was too far away from the head squish area. So, there was a large amount of cool, unburned hydrocarbons that never got taken care of. Remember that the squish area needs to be 0.040" or less, but the OEM design left at least 0.080" on most of the big blocks. The open chamber killed their "problem" which was caused by leaving the piston top too far down at TDC.

If you make sure to get the piston and the head squish area to be within 0.040" of each other, though, I think emissions will be better and depend more on camshaft and carb setup.

it is too bad that Edelbrock didn't put a better chamber in those heads, as was said before they had several examples of better chambers in production! Perhaps they were concerned about high compression dome fitment. Using the 915 chamber made sure that high compression domed pistons would fit.

R.