67 Pontiac 400 w/670 heads. Need Advice - Pontiac GTO Forum
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post #1 of 5 (permalink) Old 08-08-2017, 10:49 AM Thread Starter
 
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67 Pontiac 400 w/670 heads. Need Advice

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.

1965 Pontiac GTO
400CI
Turbo 400
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post #2 of 5 (permalink) Old 08-08-2017, 01:36 PM
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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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post #3 of 5 (permalink) Old 08-09-2017, 03:02 PM Thread Starter
 
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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

1965 Pontiac GTO
400CI
Turbo 400
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post #4 of 5 (permalink) Old 08-10-2017, 10:03 AM
 
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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

Last edited by 1968gto421; 08-10-2017 at 10:04 AM. Reason: spelling
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post #5 of 5 (permalink) Old 08-10-2017, 10:07 AM
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Quote:
Originally Posted by Nelson Musgrave View Post
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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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO General Discussion

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