[pnondahl]

Hi everyone. I'm new to the board. I have a 65 gto 389 tri power 4 speed 3.55 posi. My question is this. I have a chance at a pair of 6X heads. Will they bolt up to a 65 389 block? Will the 65 intake bolt up to the heads? These are the good heads with the screw in studs and guide plates. Any and all answers and opinions appreciated. Looking forward to being a board member. Thanks.

[pnondahl]

Hi everyone. I'm new to the board. I have a 65 gto 389 tri power 4 speed 3.55 posi. My question is this. I have a chance at a pair of 6X heads. Will they bolt up to a 65 389 block? Will the 65 intake bolt up to the heads? These are the good heads with the screw in studs and guide plates. Any and all answers and opinions appreciated. Looking forward to being a board member. Thanks.

[gtoric]

6X heads are low compression heads, 7.6cr (101cc), 2.11"/1.66" valves, with the 350ci and 400ci engine, from 1976-79... If you're looking for a low comp head, this is the last of the breed.

[b-man]

There are 2 different 6X heads. The 101cc 400 6X has a a secondary stamp '8', the 94cc 350 6X head has a '4'.

You can see the '8' or '4' stamped on the side of the projection next to the valve cover rail on the sparkplug side of the head. The 350 6X heads would be ideal, with a little milling you would have a nice 8.5:1 compression engine that is pump-gas friendly.

The 400 6X heads can be milled to get compression in the low 8:1 range. You may get a bit more compression if your engine has been bored oversize .030" or .060".

If you keep the head milling to .030" or less you will have no troubles fitting the intake, otherwise you'll have to mill the intake side of the head to compensate.

Yes, the '75-1/2 -'77 6X heads will bolt onto the '65 389 block (or any other Pontiac block). The '65 Tri-Power intake will bolt up as well. You will have to fill the 'dead hole' above the exhaust crossover on the right head with steel filler epoxy and use the '65 -'71 intake gaskets to seal the crossover.

Here is some info on crossover matching by Jim Hand.

[pnondahl]

Thank you everyone for the advice. Sure is a lot to think about when you want to make changes. Will try to put it all to good use

[engineer]

what is wrong with the heads you already have?

[65goatman]

Has anyone else used a set of 6X-4 heads on a 65 389 block? I'm considering the same combination as I want to drive my GTO more and currently have my motor apart and waiting my decision of heads/pistons for the rebuild. The advantages that I see with the 6X heads are: hardened valve seats, screw in studs and guide plates, 2.11 intake, better flowing head. My dilema is what kind of piston to use. Several people have told me that I can use the 389 piston with a mild cam. Does anyone know if this will work?

[Ron Landis]

You will need to utilize the later {'67 & up} pushrods. as 20 degree heads take a different lengt than the later 14 degree heads.

[Ron Landis]

PS...Sometimes a different piston is required or at least modify the early originals for valve clearance.