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-   66-67 GTO Tempest & LeMans TECH (https://forums.maxperformanceinc.com/forums/forumdisplay.php?f=430)
-   -   compression (https://forums.maxperformanceinc.com/forums/showthread.php?t=412829)

copierfixer 07-13-2005 08:12 AM
i have a set of '67 6x and 670 heads. what are the compression ratios of these? i think pretty high. can they be made to run on pump gas? thanks in advance for your help.
paul

Brew 07-13-2005 03:39 PM
The 670s are considered a little small for todays pump gas, for the most part. You'd have to be a heck of a tuner and have exactly the right cam to make them work without fear of detonation. Or you could have your pistons dished to get to a more pump gas freindly compression ratio. Mid-70s 6Xs should be fine for a 400, or a 455 for that matter.

Brad B. Hillebrand 07-13-2005 06:09 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Brew:
The 670s are considered a little small for todays pump gas, for the most part. You'd have to be a heck of a tuner and have exactly the right cam to make them work without fear of detonation. Or you could have your pistons dished to get to a more pump gas freindly compression ratio. Mid-70s 6Xs should be fine for a 400, or a 455 for that matter. </div></BLOCKQUOTE>

What? Can you explain the 670 a little further?

karl emerick 07-13-2005 07:56 PM
the 670's would come about 10.75 : 1 CR on a 400 with std pistons. believe they CC in the high 70's.
the 6X's come in at least 2 chamber sizes - 91 and 101 CC. with the 6X '8's (101 cc) I'm running about 9.2 : 1 CR on a 455.

racerboy 07-14-2005 05:43 AM
670s had a factory listed cc of 72, but that was probably optimistic. My wife's uncle used to race Ponitac stockers all through the 60s-70s, and said they never got set of Pontiac heads (not even RA IVs) that delived the advertised ratio. They always had to mill them.

I run 670s on my 67 428. I have a small dish in the piston with a 744 cam. Car doesn't ping on 94 octane, but I do mix toluene with my fuel. Whe I rebuild the orignal 400 HO for my '67 (with 670s), I plan on dishing the piston enough so I don't have to mix fuel anymore.

Perses 07-18-2005 08:35 AM
racerboy... how much Toluene do you mix into a tank of gas with your '67 ?

racerboy 07-18-2005 09:06 AM
Scott,
I have the formula at home (I took it out of a Buick GS Facts and Fugures book). I will post it later this evening.

RJGTO67 07-18-2005 05:48 PM
I would appreciate that formula because my 400 sure doesn't like the 93 octane we have here. Are you guys also using a lead additive?

racerboy 07-19-2005 03:38 PM
Check out:
http://www.gnttype.org/techarea/misc/octanebooster.html


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