Comp Cams...trouble in paradise?

sence were taking about brand X cars that kicked but. my buddy had a 67 firebird that came originally with a 326. he found a wrecked GTO in the bone yard with a freshly rebuilt eng(old timing chain, piston and cam in the truck.
He broke two Munch 4 speed with it before he finally when with a turbo 400 auto.
We didn't race it much but every time someone wanted to we did. never lost a race. My 73 318 was one of those victims.
From the number on the block, we determined that it was a XX 400 or a xx 428 the letter that decide the eng was 400 one year and a 428 another year.
It would rev and pull to 6500, But ran faster shifting a 5500. was a real big torque monster.