Pontiac GTO Forum banner
1 - 8 of 8 Posts

·
Registered
Joined
·
10 Posts
Discussion Starter · #1 ·
My '66 is pretty much original and documented with 2 exceptions. First, the factory 2-speed Powerglide was replaced with a 3-speed TH350. The other big departure is the previous owner had the engine rebuilt and the engine builder put '67 "670" heads on a '66 "YS" block 389.

Why would he do that? Is this a common mod? I can assume that it breathes better, but what else?
 

·
Registered
Joined
·
453 Posts
The "670" heads are actually very good heads. They have the large valves, and they have pushrod guideplates. The 389 heads have the smaller valves, and do not have the performance potential of the 670's. Somebody either replaced the heads for the performance edge that the 670s provide, or the original heads had a problem and were replaced by what was available at the time.
 

·
Registered
Joined
·
321 Posts
:agree
Unless you're going for originality or date-correct parts, stick with the 670's. Some folks claim the 670 to be one of the best heads Pontiac made. They have 2.11 intake and 1.77 exhaust valves and a 72cc chamber, vs. 1.92 intake/1.66 exhaust on the 092 and 093 GTO heads. Main difference I know of between the 092 and 093 is the combustion chamber size...the 092 has a 68cc combustion chamber and the 093 has a 70cc chamber. Plus the 670's are kind of rare, only having been offered for the 1967 model year. I think the GTO actually ran a 093 head, but the valve sizes are the same as the 092. I've got a set of 670's on the work bench, just spent a wad on new Ferrea valves, hardened seats, Comp Cams springs, locks, retainers, valve guides, roller lifters, ARP studs, etc etc. They're going on top of the 461 stroker I'm building. But I'm always looking for another set.... I'm running a set of 092's somebody before me put on my '67 Lemans, they are correct for a '66 389, although I believe they are 2-barrel heads. Interested in trading for the 670's by any chance? :eek:

KB
 

·
Registered
Joined
·
454 Posts
the 670's are very good heads the only problem being that they are closed chamber,in 68 Pontiac went to open chamber heads which had much better flame travel
 

·
Registered
Joined
·
321 Posts
Jeffs386 said:
the 670's are very good heads the only problem being that they are closed chamber,in 68 Pontiac went to open chamber heads which had much better flame travel
True. I've read stuff debating the pros and cons of both open and closed chamber heads. Proponents of closed chambers claim they give you a better squish band, and better overall burn, but they also increase compression due to the smaller chamber size. To run on the crap they call gasoline these days, you nearly have to do something like dishing the pistons to lower compression. BTW, noticed gas jumped another $.10 today around here. Went by the car wash to rinse the pollen off my truck, it was $2.49. Rode back by three hours later and it's $2.59. Did some 3rd world dicator fart today and cause yet another panic among the oil speculators and traders? Maybe I just missed that one... I'm drifting off topic here, but what the hell... call it what you will, but it seems to me that globalization and the new global economy is just another term for a global fooking for the working stiff in this country. Stepping off my soap box now...
 

·
Registered
Joined
·
84 Posts
A major change between the 68 and 67 heads is the angle in which the valves are installed in the heads, which was changed to improve the flow in the mid lift ranges. Changing the valve angle improved the short turn radius in the exhaust port and killed some to the turbulence that the early heads had. I've seen some cases of piston to valve clearance issues, since the angle change makes the valve on the newer head miss the relief cuts in the early pistons. Unless you know that the pistons were recut, I'd keep it out of the valve float range.

Another post mentioned the round port heads that came out as the "68 1/2" heads in late 1968. They are similar to, but different from the true Ram air IV heads of the 1970's. The 68 1/2 heads looked pretty trick and had a the first round port version of the high output or H-O heads. In spite of their looks, the 68 1/2 heads did not offer significant flow improvements over the 670's
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #8 ·
Thanks for the help.

Got the carb rebuilt and an electronic ignition (Pertronix) installed, plus got the timing set right which was tough because the cam is an "unknown aggressive street cam".....picked it up from my buddy's shop today.

WOW.

Next improvement will have to be to add posi-traction to my open rear end.
 
1 - 8 of 8 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top