# Cylinder Heads



## hyfye (Jul 15, 2013)

I purchased a 67 GTO about a year ago and the care does not seem to have the power that I would expect. I put on a new quadrajet, HEI ignition, and Headman Headers. The Heads are stamped 46 and I want to replace them with 670 Heads. I have seen remanufactured 6X heads for sale. I have 2 questions; am I doing the right thing and is there a difference between the 670 and 6X heads?
John


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## geeteeohguy (Feb 2, 2008)

670 heads make great power and are original equipment for your car. That said, you can't really use them anymore on a street car. They have too much compression and need too m uch spark advance to be viable. Unless you have an unlimited supply of 100 octane fuel. You want a cylinder head with about an 84-90cc combustion chamber to bring your compression down to around 9--9.5:1. That, and a decent cam will help you in your quest for power. The Wallace Racing site has a list of head casting numbers, and their combustion chamber volume. It's a ballpark list. Some heads vary from others, and the thing to do is to measure the chambers yourself. I use a graduated syringe and ATF, but there are other ways to do it, as well. Also, what are you comparing the power to? These cars, while screamers, are not as fast as some of the new muscle. When I first started driving GTO's in the '70's, I was the king of the street. I'm still driving the same cars, but I'm no longer the top dog....the new supercars simply have more power. Expect a well sorted out streetable 400 Pontiac to be pretty impressive, though, with about 300-400 reliable horsepower readily available.


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## hyfye (Jul 15, 2013)

Thanks for getting back with me. I don"t think that the 400 is original. I even switched the transmission to a 700r4 with 2500 stall and that helped a little. I still can"t even spin the tires. The motor runs smooth, sound great but can't get out of its own way. I had a goat back in the day and could smoke most cars on the road like you said. I did a compression check and each cyclider is measuring about 150. The motor has a cam in it and I think its a mismatch with the heads


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## Instg8ter (Sep 28, 2010)

What rear end gear are you running, some are as tall as 2:54 and will not be light to light screamers, but will perform well on the highway all the way up past 120 MPH.


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## geeteeohguy (Feb 2, 2008)

My de-tuned (low compression small valve heads) bone stock '67 400 in my ragtop will smoke the tires in the rear (2.56 posi) with no problems at all. I am running the original points distributor, carb, intake, and exhaust manifolds. Something is wrong with your engine set up.....150 psi is about perfect for compression, so it's not the heads. 46 are small valve, but work well on the 400. My suspicion is that the cam is installed incorrectly, probably very retarded. You need to degree the cam to verify that. Pontiacs tend to like an advanced cam. Throw a vacuum gauge on it and see what the manifold vacuum is. Should be 20-21" at idle. Also, snap the throttle in neutral....is it sluggish or does it pick right up? Again, my bet is that it has the wrong cam, or a mis-installed cam. And that will make or break how an engine runs.


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## BearGFR (Aug 25, 2008)

It should run better than that even with one cylinder tied behind its back 

Start with the basics. Tune-up, ignition timing (total, not initial), carburetor, etc.

Bear


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## hyfye (Jul 15, 2013)

Thanks all of you I think I will take it up and get it dyno'd and see what is in iy


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