[Onebadjudge70]

I have a bone stock 77 400 engine with 6x-8 heads. It runs good and I only bought it to get my GTO mobile again. I have a good set of #12 heads that I'm thinking of putting on and maybe sticking in an 068 cam. I have a performer RPM intake and RA 2 1/2" manifolds which will be running into a full Pypes 2 1/2" system with an X-pipe. Will I need to run 93 octane? Worried about detonation, any thoughts on this combo?

[shaker455]

I would make a more modern selection on the cam, they are prone to detionation.

Yes 0n the 93

[zeebo]

im looking into doing something very similar with a 73 400--using 1970 #13 heads which in the books are 72cc, and if mine check out to be that, ill have them opened up a little to like 75-77cc, which according to the calculations for a stock block and piston 400 comes out to about 9.6:1 compression.

[Kenth]

Originally Posted by Onebadjudge70

I have a bone stock 77 400 engine with 6x-8 heads. It runs good and I only bought it to get my GTO mobile again. I have a good set of #12 heads that I'm thinking of putting on and maybe sticking in an 068 cam. I have a performer RPM intake and RA 2 1/2" manifolds which will be running into a full Pypes 2 1/2" system with an X-pipe. Will I need to run 93 octane? Worried about detonation, any thoughts on this combo?

It´ll work fine.
With the chamfered pistons and the late closing intake valves of the 068 you may use a lower grade fuel.

[Kenth]

Originally Posted by zeebo

im looking into doing something very similar with a 73 400--using 1970 #13 heads which in the books are 72cc, and if mine check out to be that, ill have them opened up a little to like 75-77cc, which according to the calculations for a stock block and piston 400 comes out to about 9.6:1 compression.

Most books are wrong regarding Pontiac cylinder head sizes.

You may be surprised measuring the #13 chambers?
They have been found to be around 80cc´s stock.

Stock #12 heads are 66-68 cc´s.

Also, your 1973 400 are using flat top pistons were TS´s engine uses the chamfered pistons, so the end result may end up similar between the two engines?

[zeebo]

Originally Posted by Kenth

Most books are wrong regarding Pontiac cylinder head sizes.

You may be surprised measuring the #13 chambers?
They have been found to be around 80cc´s stock.

Stock #12 heads are 66-68 cc´s.

Also, your 1973 400 are using flat top pistons were TS´s engine uses the chamfered pistons, so the end result may end up similar between the two engines?

well that could be good too if they cc out at 80cc..that would still make my compression around 9:1..and now id have room to mill them slightly if need be....

[rad400]

I have 12 on a 74 block stock bottom end Crower 60210 cam. No detenation must have good cooling system timing spot on. alittle rich on carb. Trw pistions .030 over.

[FrankieT/A]

Originally Posted by Kenth

It´ll work fine.
With the chamfered pistons and the late closing intake valves of the 068 you may use a lower grade fuel.

X2!

[geeteeohguy]

I ran #12 heads on the '67 400 in my '67 GTO with an 068 cam on 92 octane when it was available and it pinged and detonated as bad or worse than it did with the original 670 heads. Not even remotely workable for me, in CA, where it's hot and dry. And this was 20 years ago, when gas was better than now. Way too much compression for todays gas, IMO. Your luck may vary....

[tom s]

Dont guess!CC the heads.Tom