# 77 heads on 1966 block



## Tony Arnold (Apr 26, 2014)

Rebuilding a 1966 gto. Engine builder has told me that my 093 heads due to previous rebuild and grinding of valve seats cannot be rebuilt. 093 heads seem to be fairly expensive. Is there any reason that 1965 #77 heads cannot be used instead. Are there any issues with the 66 tripower intake mounting to the 77 heads? Thanks. Tony


----------



## PontiacJim (Dec 29, 2012)

Intake pattern is the same for 1965-1979. It'll work. Seeing you are not going original, why not bore the 389 out to 400CI size, use 400 pistons, and use some 1968 and up open chamber heads with bigger valves, and lowered compression (9-9.5) to make your engine pump gas friendly with iron heads. The 093/77 heads are rated at 10.5 compression unless you are using a piston with more cc's to lower the compression. If you bore the engine, mill the heads, it will go up a slight bit more.

It may be possible to save your 093 heads if you want to keep the engine original. The 421 Super Duty used a larger 2.02" intake and larger 1.76" exhausts. The Ferrea stainless steel valves catalog offers custom ground valve sizes. If your machinist thinks opening up the valve seats to the 2.02" size will get into some better material so he can perform the valve job, then this might be a consideration. Same on the exhaust as long as the heads have the room for them. You are going to use new valves anyway, right? Might only be a few more dollars to have a set of 2.11" Pontiac valves cut down for 2.02". You could also contact/email Butler Performance and run the same question by them. They do nothing but Pontiacs and am sure they can give you an answer or possibly supply you with large valves if that will work. Butler Performance - Specializing in Pontiac Engines Heads and Performance Parts or KRE at Kauffman Racing Equipment I bought my SS valves from KRE and they were $88 a set. So custom ground might not be so bad when measured against buying another set of heads that you will have to most likely want to rebuild with new valves.


----------



## Tony Arnold (Apr 26, 2014)

Thanks Jim. Block is fresh 30 over and I have a new set of dished pistons to lower compression to around 9.3-9.5/1. The builder wants to install hardened valve seats but is concerned that he may cut into water jacket. He mentioned that he would need to cut around 6-7/32" for placement of the new seats. Is there enough iron to support new valve seats in these heads? Thanks. Tony


----------



## geeteeohguy (Feb 2, 2008)

The #77 heads are identical to the 093 heads with the exception of the AIR galley on the 093's. Same exact head, combustion chamber wise. They will bolt right on a '66 389 and perform exactly like 093's: great power and throttle response for what they are. With all due respect to Pontiac Jim, whom I agree with 99.9% of the time, the overbore to .060" simply to use easy to find pistons is a mistake. Once bored to .060", you can not rebuild again withour sleeving. Also, the factory .093 and #77 heads were rated at 10.75 CR, not 10.5....the 092 heads in '66 got the 10.5 rating, and it was a 'big car' head. Hardened valve seats are not needed on these heads, unless you are pulling a trailer or a boat a lot, or cruising at 3500 rpm for extended periods of time. I have the standard seats in my '65 389 heads (#77), with no issues in.....34 years of service and about 50,000 miles. Up to you.


----------



## PontiacJim (Dec 29, 2012)

Tony Arnold said:


> Thanks Jim. Block is fresh 30 over and I have a new set of dished pistons to lower compression to around 9.3-9.5/1. The builder wants to install hardened valve seats but is concerned that he may cut into water jacket. He mentioned that he would need to cut around 6-7/32" for placement of the new seats. Is there enough iron to support new valve seats in these heads? Thanks. Tony



I have had no experience with having any heads fitted with hardened or standard (cast iron like the heads?) valve seat inserts. I do recall that installing the seats in a Pontiac head can be tricky. If not done correctly, they can bust into the water jacket -so your machinist's concerns are valid.

.030" covers the pistons. Geeteeohguy is correct that a .060" overbore might later require sleeves IF there is not enough metal in the cylinders to go any larger. Sonic testing would let you know for sure. It is indeed better to go as little on the overbore so you have metal left to go the next size when the time comes for another rebuild. You can also get pistons in .040". The machinist I used said you can get custom pistons made to any size, but it will cost you.

Geeteeohguy is the expert on the '65-'67 engine combo's so what he is saying you can take to the bank. I was just trying to offer up a solution not knowing you had the dished pistons to lower your compression -so you are good on that. Bigger '68 and up open chamber heads would lower your compression too much with your pistons, so you want to go with '66 or '65 heads with the smaller chambers to match your new pistons.

So, it is your call & your machinist. You could let your machinist attempt to install "standard" valve seats and keep your fingers crossed that he does not bust into a water passage. If he does, then you will owe him for the attempt and then you will have to get another set of heads. It seems to me IF the 093 heads can't be used in their present condition, you will have to get a different set of heads anyway -so it might be worth the gamble?


----------

