[Murf'sDad]

Originally Posted by ITSBACK

That was my reason for starting this thread. Whats the deal? Do I really have to use dished pistons with my 670 heads. I was at a car show Friday and talked to a couple of guys with 670 heads on their 67 GTO's like mine and they said they run great. I was reading Jim Hands book last night and he said the advertised 10-3/4:1 was an advertisement and that they where more like 10:1 maybe a touch higher. Did they not run great back then and my 428 put out 376hp. Why then with a bigger cam and my un ported 670's, headers, x-pipe,aluminum intake and 750 double pumper and bored .030 wont my motor run and put out 400-450hp? Some say 10.1:1 is optimum and others say 9:1.

I have a set of ported #13's on my engine. They cc out between 79 - 81. The block has been "zero decked". I measure it as about .002" "out of the hole". AS best as I can calculate is will come out at 9.8:1. With the UD cam I don't foresee having any problems with detonation on the 91 I can get around here, and get about 450 hp. If I could get 93 octane Sunoco I'd be truly golden.

Every engine is different. If you do a search you will find references to 11:1 aluminum head motors running happily on 87 and 9:1 iron headed engines that won't live on 91 with octane booster.

For the difference of 1 compression point you aren't going to lose any noticeable hp. From what I understand you pretty much can't run a 670 headed 428 on pump gas. If you want to keep the 670's, pull them off and open up the chambers a bit and drop from 10.5:1 to about 9.5:1. You'll be happier and you won't have to dish your pistons.

And while todays gas is cleaner it doesn't run nearly as good as the old stuff and it doesn't have quite the octane rating.

JMO, Stewart