# head casting # question advice



## scoob (Jul 18, 2011)

just had heads pulled on my 66 and worked # are 9778776 they are 65 389/421 heads my questions are will the performer intake i bought for a 66 fit and what are the advantages or disadvantages of these heads not sure if they were done factory as left over from the 65 run or done sometime in the past. car was all 99% mechanical origional when i bought her under 90,000 miles. please give me opinions and ideas


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## geeteeohguy (Feb 2, 2008)

The 76 heads are 1965 big car heads. The GTO 389 and big car 421 heads were 77 casting number. The 76 heads are 10.5 compression, the 77's are 10.75. The disadvantages of these heads (76 and 77) are the closed chamber design, (prone to pinging), small valves, and press in rocker studs without pushrod guide plates. Both heads have small chambers, and require 95-100 octane to run with standard flat top pistons. That said, they work quite well on the 389's and 421's....my '65 has the original spec 77 heads, and runs super strong...but it needs race gas. A little while ago, put a 389 together with a friend using the 76 heads and dished pistons (for a 9:1 CR) and his engine pulls like crazy with an XE 268 cam...it feels as strong as mine, and runs on 87-89 pump gas! The intake you bought will bolt right on with no issues. Stock intakes tend to work better on these engines than aftermarket, however. The 76 head has a slightly bigger chamber, at about 69cc, than the 77's, which usually cc out at about 64-66. The valves are the same in both heads. So, 76's would actually be preferable on today's poor gas.....


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## BearGFR (Aug 25, 2008)

:agree Nailed it.. he did.

Bear


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