Q: 670 Heads
Should I use my 670 heads or switch to something else. I have heard the 670 are closed chamber heads and the valves are shrouded. You would do better with some 62,16,12,13, or 48’s.
A: While you are right about the shrouded valves, I find it interesting that Pete McCarthy writes the following in his “Pontiac Racer’s & High Performance Handbook”:
“The 670 heads are unique in a number of ways:
I was and is the only late closed chamber design.
The intake port is the best flowing of any production head including the Ram-Air IV.
It is the only big valve head with exhaust port air injection holes, although a number if Eastern cars didn’t have them.
It was the first in a long line of high performance Pontiac heads with screw-in studs and stamped steel pushrod guide plates.
If one obtains these 670 heads, and opens the chambers ala the 1968 and later 400-428 heads, and adds the good valve prings, you will have as good a high compression head as is possible to find. The 670 head is one of the great junkyard buys available.
That’s pretty impressive. I imagine that the removal of the material shrouding the valves, plus enlarging the chamber to match the better quench area of the 1968 and later heads, one would also shave a couple 10ths off the compression ratio, ending up somewhere in the are of 9.75 or 9.5 to 1. Remember that Pontiac overestimated compression, so a rated 10.5 to 1 was closer to 10 to 1.
If you were looking for a decent head to use without modifications, and found the 670s at a good price, they are worth buying. If you were interested in making the above modifications, you would end up with dynamite heads.
By chance, the 1968 YS block (GTO/big car) in my car came with these heads. After reading McCarthy’s comments, I decided to hang on to them.
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Content last modified: January 16, 2014 at 1:16 pm