[lintmann]

I'm just wondering if anyone can tell me what the difference is between these two heads and was the #76 head ever used on the 65 GTO?
Thanks

[Jerry H.]

Slight difference in CR. And no the 76 head was never used on a GTO engine. Period.

[lintmann]

Thanks Jerry. I had a hunch that the #77 was a GTO only thing but now I know for sure.

[Old Goat Racer]

The #77 head was also used on the 389/421 in Cats & Bonne's

[440sixpack]

Is there any visible difference between a 421 and 389? and you're saying the 77 heads will work on either?

I have to find a date code correct 65 engine and so far I've found more 421's than 389's. but I don't want it to look wrong.

[Jerry H.]

OK, maybe some misinformation can be taken from some of the above posts. The 77 head came on the 389 in the GTO, never a 389 that came in a big car. The 77 heads also came on the 421HO that came in some of the big cars, but not any of the regular 421's or 389's in big cars. The non HO 421 head was a 76 as were most of the 389 heads. There was also a low compression head for the 389, I don't remember the casting code for it offhand.

There is very little difference between a 421 block and a 389 block. The 421 has a
'triangle-like' lug near the distributor hole that the 389 block doesn't have. Also the front of the block fits flush with the bottom of the head on a 421. The 389 block has a little 'dip' or valley that shows when you have the head mounted. And yes, the heads are interchangeable between the 389 and 421.

[440sixpack]

Thanks for the info, looks like I need to find a set of 77 heads.

Is there a visible difference between the 400 and 389 or would the 421 pretty much discribe the 400? but then I couldn't use the closed chamber 77's on my 400 block anyway I guess. better just find the right 389/

[Old Goat Racer]

I stand corrected on the 389/77 head in the Cat/Bonne.
I used to know these answers like the back of my hand. No one has asked me these questions in years. Good to know there is still a thirst for knowledge.
My info shows the 421 356-376 HP with 3x2's used the 77 head.
Not sure where the 20 HP diff was. Exhaust manifolds?
#75 was the 8.6 head.
I just sold my set of #77 heads after 29 years, so they are still out there.

Never too old to learn, or to be retrained.

[lintmann]

Thanks for the clarification Jerry. I've been looking for a while now for some April 65 #77 heads(block too) without much luck so I got to wondering if those #76 heads would be okay but I see now that they aren't right.

I can't believe that it's so hard to find these heads. I know it's some 40 years ago but I mean they made like 75,000 of them so there should be some around.....right?

[MIke L]

Lintman
I also have an Apr '65 [4th week] built GTO with the 389 and #77 heads!

I hope you find yours

Mike

[geeteeohguy]

Mine was built April 29, 1965 at Fremont. It has the "77" heads as well....and is a 360HP car. (the original block is long gone, though).

[MIke L]

Hey we got 2nd cousins!
On my Car Billing History card I got from PHS 19yrs ago, the only date on it is the Invoice Date of 5/5/65. Built in Pontiac

Mine is as well, the tri power was gone tho when I got it.
It came with a 4:11, but changed to a 3:55 for better cruising. [still have all the pieces

Mike

[lintmann]

Mine is a Fremont car too built the second week of May 65. The original engine is obviously gone and it has a 66 WT block with late June #77 heads.

I was suprized to see them on that block so last summer I pulled the valve covers hoping that they were the originals but I wasn't that lucky.

Mike, are you saying that you have a spare April 389 and #77 heads or that they are in your car?

[MIke L]

No, that's what in the car.
Sorry, I wish you luck in your search

Mike