From my experience, these engines are not making more horsepower at the higher rpm above 6K. About all you are going to do shifting up there is drop a valve, if you are running stock valve springs. A friend's L78 with more cam shaft and head work, ETs best shifting at 6K. Our L78 and L72 are both 4 speed with 4.10 gears. The 427 is a ton stronger in all rpm ranges. The bottom end torque and the extra hp on the top end make a bigger difference than the 31 cubic inches would indicate. Perhaps the bigger bore unshrouds the valves allowing for better breathing. The minor differences in cam shafts would make an insignificant difference. I wouldn't put much credence in factory ratings. The numbers look good on the breather though.
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Chevelleless after 46 years......but we did find a low mileage, six speed, silver 2005 Corvette. It will just have to do for now.
