Pontiac GTO Forum banner

1 - 5 of 5 Posts

·
Registered
Joined
·
93 Posts
Discussion Starter #1
Gents,

I have run across a 66 389 (YS) block that has been bored .40 over for a decent price and from a guy I trust. However, the heads are not coming with it. There is a set of 670 heads for sale that I have thought about picking up until I can save up some $$$ for a set of heads. I do have a set of bare 093 heads that I'm thinking I might have rebuilt in the future.

I have read many, many, threads regarding compatible heads for a 389 and I still don't have a definitive answer. The engine I'm looking at has a stock cam (according to the owner). Would the 670 heads fit?

Thanks for any feedback.
 

·
Registered
Joined
·
3,761 Posts
Yes, but you will most likely have to "notch" the cylinder bore due to the larger valves and different valve angle. You will also have to use the 400CI piston UNLESS you get 389 pistons with the correct 400CI valve notches in the top of the piston. You will also wind up boring the block to .060" over in order to use the 400CI pistons.

So the question becomes, if it cleans up at .040" and you can use the block as is, you still have the option later to overbore the block again rather than going .060" now and having to sleeve it should you want to rebuild the block in 30 years.

Just read this article which should clarify things for you: http://www.gtoforum.com/f12/389-400-conversion-118561/

Ask and you shall receive. :thumbsup:
 

·
Registered
Joined
·
93 Posts
Discussion Starter #3
Jim, you rock! I guess I'm going to pass on the heads. Might as well put up the $$$ for some Edelbrocks.
 

·
Registered
Joined
·
634 Posts
DSS makes pistons for use in 389 with late iron or E-heads.

https://butlerperformance.com/i-24453706-dss-forged-pontiac-flat-top-pistons-389-3-75-str-4-080-or-4-100-bore.html?ref=category:1234874

Can probably buy custom Auto Tec pistons in whatever bore size & pin height you want. For less than $600.

Might also wanna consider a stroker assembly, with custom Ross pistons.

https://butlerperformance.com/i-24591340-butler-performance447-454ci-balanced-rotating-assembly-stroker-kit-for-389-block-4-250str.html?ref=category:1234862
 

·
Registered
Joined
·
93 Posts
Discussion Starter #5
Thanks bigD. Right now I'm just looking for something that will work with the engine without throwing further $$$ at it at this time. I'm still trying to finish up a mustang project that's sitting in my garage.
 
1 - 5 of 5 Posts
Top