Here is a REAL LIFE test to help answer your question:
My friend, Justmoparjoe, had a 408 with aftermarket heads in his cuda and ran 7.2's at best in the 1/8. He went to the 400, stock crank, with aftermarket heads and went 6.8's if I remember correctly (could have been 6.7's)???
So, the 400 gave up cubic inches to the small block and ran faster. Same car, same gears.
