80_cutlass

Perusing some OLD posts and came across this:

"just don't use the 3A heads...."

more to the post in regards to 5a heads which I know about.

But why the dislike of the 3As? Poor exhaust port flow? What else?

sb

70 cutlass s

3A heads where late model 350 which was a low compression engine. 5A heads are early 80's to mid 80's 307 heads. Your talking about small valves. They don't flow the greatest. For a 350 build it is better start off with 5, 6,7, or 7A. Just better heads easier to get more power out of something that was built when engines where built for higher compression. 3A you can use them it just cost more to get them the way you want them. Keep in mind if using older heads on a late 70's engine you have to get the bolt holes drilled out to 1/2 inch.