[north]

I suspect the fact that they couldn't sell the 455 in the F bodies was a reason they didn't make a true high-performance version of the 1970 455. Also, the long stroke of the 455 on the stock bottom end of the 1970 455 wasn't compatible with the high rpm characteristics of the RA IV cam and valve train.

The closest to that was the 73-74 455 SD, it doesn't take much to imagine what 25% more compression and the high lift duration of the RA IV valvetrain would have done to the power band.

[scott70]

Originally Posted by north

I suspect the fact that they couldn't sell the 455 in the F bodies was a reason they didn't make a true high-performance version of the 1970 455. Also, the long stroke of the 455 on the stock bottom end of the 1970 455 wasn't compatible with the high rpm characteristics of the RA IV cam and valve train.

The closest to that was the 73-74 455 SD, it doesn't take much to imagine what 25% more compression and the high lift duration of the RA IV valvetrain would have done to the power band.

My 70 455 has its original 64 heads ported to 254 cfm, port matched iron intake and a ra4 sized hft cam. Made 490hp at 5200/570 trq. I would think that’s well within the rpm safe range ,,, no need to spin anymore the 5500 rpm’s.

[Baron Von Zeppelin]

RoundPort heads and IV cam with 1.65 rockers will spin past 6,000+ rpm
That's why most Ram4 cars have replacement engines.

Guys would have been doing the same thing with their 455's if Pontiac put all the goodies with them.
Which they should have, and had plans to, but didn't.
Would have been a lot of warranty repairs even with better rods.

067 and 068 camshafts with stock springs were like built-in rev limiters