Jeff 32
I am so glad you started this thread. I have a pair of 420's that are due for a rebuild and I am looking to get 500+ out of each for my '89 Formula F311. Lets keep this discussion going.
See link - http://www.offshoreonly.com/forums/s...d.php?t=137967

I read your tread and there's good info there too. In fact it seems like my heads (don't know how many though) are cracked. Other than that I know I have a cam with 15 milimetre less than it's supposed to have on a lobe. But I'll keep the info coming here, I guess tomorrow I'll have the whole diagnosis and possible rebuild solutions. Besides, I certainly thought about 2 HP500...

Whats the difference between the 400 and 420?

The 400 had a dual plane intake and a Quadrajet. Also had those log exhaust manifolds with 3" outlets.