OK, I am still preparing for the engine build in my 66. My engine has smog heads on it and I think I am planning on replacing with non smog and saving the originals. My question is I have located two sets of heads locally, one is 65's and the other are 66's. Are there any differences? I am thinking not but I want to be sure. Thanks

 

If you give me the casting codes, I can look it up in the bible. Generally, the heads will be basically the same. The smag heads (as discussed on another thread recently will have humps in the exhaust ports for the air injectors. But these can easily be removed. The valves will be the same size, butr there were three differnect combustion cahmber sizes. from memory there the norm was 58cc. one was samller one was larger, which will affect your compression ratio.
For me, the biggest difference between a 65 head and a LATE 66 head is the rocker system. The 65 will have close tolerace slots as the push rod holes, which act like push rod guides. Late 66 have the rail type system, which is prone to dropping valves when worn.

 

Thanks, my thought was rather than modify the smog heads, I could purchase used (cheap $50-60) and have rebuilt to avoid removing smog junk. A local guy has 65 heads, which I'm guessing will work on my car. Another guy has 66 heads he thinks are off a fairlane. I didnt know if all 66 heads had been changed somewhat, and I just want to make sure the 65's would work for my block. Thanks for any info.

 

I didn't know any '66s had "smog heads".

 

The 66 heads number c6oe

 

Straw, I'll look them up for you.
Texas, Yep some 66s had smog heads. Mine included. I think it was the Californian cars.

 

just remember those old heads will need hardened ex seats installed to use unleaded gas. you may want to look into a set of GT40P's cause you can get a set done with bigger valves and stiffer springs for 600 bucks. really, by the time you shell out for another set of 289 heads, pay for a vavle job and hard seats, you'll be @ 600 bucks anyways and the GT40's would be much better heads.

 

My understanding is the GT40Ps have a different spark plug angle and so require different headers, as the std manifolds wont fit. The gt40s will fit Ok though. Can someone else confirm this?

 

Yeah, P heads require P headers because of the plug angle. They barely flow better than standard GT40's, but P's seem easier to find.