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post #1 of 15 (permalink) Old 07-21-2010, 10:51 PM Thread Starter
 
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67' 670 Heads

I've just purchased a great set of 670 heads. After reading the info you guys helped me out with(Exhaust Dilemma) Mitch made a statement concerning my heads needing to match cc's to avoid having to change my pistons. My 7H1 Heads are 80cc's, The 670's 67/72cc's. Was hoping someone could shed a little more light on the subject. Thanks.
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post #2 of 15 (permalink) Old 07-22-2010, 05:43 AM
 
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The new heads have a smaller chamber, raising your compression ratio even more. You need dished top pistons to run those heads, or racing fuel.. With a flat top piston that would be about 11:1 compression. The max a cast iron head can run on Premium fuel is 9.5:1.

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post #3 of 15 (permalink) Old 07-22-2010, 08:50 AM
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You could run them, but you'll have pinging and need to retard the timing a ton. Or like mentioned run race fuel. Which gets to be expensive. I drop about $50.00 for less then a half a tank to mix with premium.
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post #4 of 15 (permalink) Old 07-22-2010, 09:15 AM
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670 heads are one of the most effective heads for making power--they're excellent heads. That said, they are the last of the closed chamber, early style heads with the big valves. They were designed for 100 octane fuel, cheaply and readily available in the '60's. Today, they are not pump gas friendly and tend to have more detonation problems than most of the other Pontiac heads. If you run them, you need to run dished pistons so that your combustion chamber is about 80-90cc.
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post #5 of 15 (permalink) Old 07-22-2010, 03:39 PM Thread Starter
 
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Got it. Thanks.
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post #6 of 15 (permalink) Old 07-22-2010, 04:37 PM
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They need to make a shim like the 'head saver' shims for OHC 4 cyls. Used when you machine the head surface so far it messes with the valve timing. One the right thickness to drop the compression a point on a V-8 would be cool.
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post #7 of 15 (permalink) Old 07-22-2010, 08:08 PM
 
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Originally Posted by Rukee View Post
They need to make a shim like the 'head saver' shims for OHC 4 cyls. Used when you machine the head surface so far it messes with the valve timing. One the right thickness to drop the compression a point on a V-8 would be cool.
Right, I want the big HP heads, but between race gas and lead additive I'm leaning towards the 6X heads and letting the 60's head rot in the corner.

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post #8 of 15 (permalink) Old 07-22-2010, 08:27 PM
 
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Quote:
Originally Posted by Rukee View Post
They need to make a shim like the 'head saver' shims for OHC 4 cyls. Used when you machine the head surface so far it messes with the valve timing. One the right thickness to drop the compression a point on a V-8 would be cool.
They are cometic head gaskets, but that thick of a gasket can cause other issues.

No way will 670s run pump gas on a 455 for sure, maybe on a 400 if the slugs are down the hole and you are at a higher altitude in cool air, like Denver. I knocked the upper rod bearings out of a 400 on 93 with an octane booster, so I found out first hand what happens. They also liked lots of ignition lead, the 455 I used to run them on liked 52 total, that is a lot. It would slow down almost a full second if I dropped the total timing to 38. Not the most efficient chamber design.

I have a set or ported 670s I am putting on the 70 GTO's 455. Why would I do that you ask? Well I have E85 available all the way back to Nebraska where I grew up, and I make my own ethanol fuel too, so I can run lots more compression. Why not run as much as you can get if your fuel can handle it?

If you have E85 available in your area, it is way cheaper than race gas, runs cooler, and is usually even cheaper than 87 pump gas. You can get a Holley already set up to run it, or you can send me a Qjet and I will convert it for you, provided you have E85 near you. So far I havent found any problems with running it in my 70, but you cant switch back and forth from E85 to gasoline with a carb, its one or the other. The only changes I made were an electric pump years before I started running E85 in it, and modifying the carb to flow a bit more fuel. The rest of the fuel system is stone stock from 1970.

If E85 isnt available near you,then find some 6X or 5C heads and run pump gas all day with them. In some states its hard to find, but as a way to make lots of power on the street for cheap, its worth the effort to run it. E85 is the only thing that comes out of a gas station pump that you can run with that compression.
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post #9 of 15 (permalink) Old 07-22-2010, 09:35 PM
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A good friend of mine used to run the '67 we're putting back together now on alcohol back in the early 80's. He took the jets OUT of the carb. It got about 4mpg, but ethanol was cheap, and he was able to run a ton of advance and full compression. The car ran cool and had a TON of power. Ran it strictly on the street as his ONLY means of transprtation. The whole problem with these engines is that we're trying to feed them fuel they were not designed for. So, we can leave them stock, and de-tune them to the point where they barely pull the car but won't ping, or we can install new-technology parts into them so we can run 90ish octane fuel. (Or we can run av gas or alky). I run a stock compression 389 in my '65, and it's a stickshift with a lot of cam and decent gears. I have to use octane booster/race gas. I broke multiple pistons in a 428 I had due to pinging...and no, I didn't hear a thing. (And I have good hearing---or did then, anyway). I run low compression heads on my '67. Does it run as strong as it did 25 years ago when it had the 670's on it running leaded high octane? NO WAY. But it does run well, and I drive it everywhere on 89 octane pump gas. Pontiac engines hate having the piston "in the hole". They like a zero deck, and even if compression is higher due to this, they will rattle less because the in-the-hole motor has a crappy flame front with the piston below deck. Hot spots and uneven combustion. It's all about the research....A lot of guys seem to be putting together 9:1 stroker motors that make monster torque and run on regular. It's a brave new world......
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post #10 of 15 (permalink) Old 07-24-2010, 06:42 AM
 
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I have the same heads, and concerns. Someone mentioned dishing the pistons, how much, and would it effect the engine balance? I have TRW pistons and have been told they can be dished. I don't want to scrap the heads as this is an original 67 RA motor.
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