# 670 heads



## harleynut45 (Nov 22, 2011)

This might be an old subject but I continue to be confused about it. This past week my GTO club sponsored the GTO 50th Anniversary National Convention in Pittsburgh. I worked the Convention and I saw a lot of cars both trailer queens and drivers with 670 heads. I drive a 67 GTO with heads off a 73 GTO. I don't know what the compression ratio is on my heads but I do know they have to be lower than 670s. Question, can I use 670 heads with the crummy ethanol gas? If I cant and they do.....what's up with that. What would be a good compression ratio to run on the street with out giving up to much HP. Might be old subject some might consider dumb but so be it.


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## pjw1967 (Mar 10, 2014)

I have been running premium pump gas for 20 years in my '67 with 670 heads. For awhile I would put in different additives. Stopped doing that about 5 years ago. I put about 1,200 to 1,500 miles yearly on the car. The only noticeable effect of $h!tty gas has been the deterioration of the carburetor(s) over time. The ethanol seemed to eat the gaskets. I got a rebuilt Q'jet last year from Ames, which they promised me was made with ethanol-resistant material. So far, so good. I have the timing set at about 9 BTC. Aftermarket temp gauge shows a steady 200 degrees on a hot day, rising a little at higher speeds. Might have to fiddle with the timing to stop that. So my conclusion would be get the 670's if you want, and don't worry about the rest. I don't.


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## harleynut45 (Nov 22, 2011)

After trying the search menu, 
I learned a lot from Bear and GeeTeeeO. Should have tried the search in the first place. Live &learn


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## geeteeohguy (Feb 2, 2008)

Yep. My 670's have been off of my '67 for over 25 years. Sitting in a corner of the shop. Even 30 years ago, they had too much compression for me to run them on then 94 octane low lead pump gas with no ethanol or MTBE, etc. Best to run an 85-95cc chambered head if you have the stock pistons.


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