# 67 Pontiac 400 w/670 heads. Need Advice



## Nelson Musgrave (Aug 8, 2017)

So, I just bought a 1965 pontiac Tempest Custom (GTO Clone). It has a 67 YT 400 w/ 670 heads. The guy that i bought it from said it had a mild cam (of course he didn't know the specs). He did not know of anything else done to it. Hell he did not even know that it was a 67 motor until i told him. So with all that said. I know nothing about these 670 heads. What fuel do i need to run? It is a street car, daily driver. i have drove it several times already with 92 octane. But please tell me if i am wrong or if I should get new heads for the street. Thank you in advance.


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## Goat Roper (Oct 28, 2014)

Welcome to the forum.
You don't know what the compression ratio is and usually if the compression has been lowered to 9.5-1 to run on the new pump gas it is done with the pistons not the heads.
Do you experience pre ignition?
My engine is built 9.5-1 and runs good on 89 octane.
You don't need new heads to run it on the street.


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## Nelson Musgrave (Aug 8, 2017)

No i do not know the compression ratio. Like i said i just bought the car and haven't torn into the motor. So far i haven't had any pre-ignition or detonation. I will find out the compression ratio soon


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## 1968gto421 (Mar 28, 2014)

Here's a thread about the 670 heads and discusses compression and other info you probably want to know. Hope this helps you some.

670 heads popularity ? - PY Online Forums


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## Goat Roper (Oct 28, 2014)

Nelson Musgrave said:


> No i do not know the compression ratio. Like i said i just bought the car and haven't torn into the motor. So far i haven't had any pre-ignition or detonation. I will find out the compression ratio soon


Does it run good?
No smoke or low oil pressure?
Why do you want to tear into the motor?


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