# Decoding Head 977877



## the65gto (Oct 9, 2008)

I got to "pokin" around with Bears spreadsheet trying to confirm my CI and calculated compression ratio. I am the original owner of a 1965 389 tripower, 360 hp and know that this is the original equipment. Anyway went to confirm the heads, there is no data on the center ports but 2 lines of numbers near cyl 2 and 7 and they are a "6" and underneath that is "77". So I am sure they are 9778777 heads. Went looking on the internet and what a bunch of conflicting information. Copied some of the data from the sources I found:
The valves 1.92/1.60,some say 1.66, others say both 1.66/1.60. 
The compression ratio is 10.5, others 10.75. 
The cc's are list as 68 or 70. 
These data list's show the 65 389/GTO as head "76" (assuming the 335HP 4 brl) and the "77" as 421/HO.

(Title missing an ending "7")


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## Roger that (Feb 6, 2010)

The 65 GTO came with head casting 77 and this head a special head that was part of the GTO package for the 389. The head was a 421 cid head. This raised the compression up for the 389 compared to the non GTO 389s. Pontiac advertised the valves as 1.92" intake and 1.66" exhaust. I have some GTO valves that I just measured for you and they are 1.925" and 1.64". They will vary some base on the manufacturer process.

Pontiac also advertised the GTO 389s with 10.75:1 compression. But if you do math with a 68cc head on a 389 it really is a little over 10.0:1 compression.

So some of your charts your looking at might be doing real math and other might say what the brochure says.


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## Lemans guy (Oct 14, 2014)

know what you mean. My 66 lemans 326 has 094 heads....

Wallace Racing says they are 9,2 compression. So does my factory 66 manual

other sites call it 8.6cr, and the valve sizes vary from 1.92 to 1.88, on various sites, some sites list both sizes.

There was a HO head that had 10.5..........I don't have that

but it sure is confusing, some sites list the 66 094 and the 67 140 as the same compression, although different closed and open chambers.

some call the 094 62cc, some call it 68cc and others confuse it with the 94 later heads i think.........

Right now I guess wallace Racing and Factory manual are leading!:nonod::nonod::nonod::nonod:


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## the65gto (Oct 9, 2008)

I just plugged in my info into Bears spredsheet and got 10.366 SCR and 400.435 CI (I am .060 over)


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## geeteeohguy (Feb 2, 2008)

What Roger said is dead on. No difference between the 4bbl and 3x2 heads. Same head was used on every '65 GTO: the 421 head. With, what were then, the biggest valves available. The '77' heads on my '65 cc'd at 64 or so after a valve job and clean up many years back. Not good on pump gas!


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