jackandjules2011

I have a pair of 1965 289 heads. The casting code is C5AE, and the date code is 4M21 and 4M16. They have screw in studs, and have been rebuilt and tested by a machine shop. The shop told me they have Chevy valves and would have at least 13:1 compression. Does anybody know how much I should sell them for?

001mustang

C5AE should have 54.5 CC comb chamber volume and be closer to 9:1 on 289 w/ stock block deck height, stock head gasket and stock pistons.

Are the heads milled to less than 54.5CC?

67mustang302

13:1 compression in what engine with what piston? 13:1 in a 347 with a pop up maybe.

As far as what they're worth, depends on whether they have port work, what kinds of springs/valves/seats etc.

jackandjules2011

Well the shop built a 302 for me, bored over .40, stage 2 cam, and they decked the block. I was going to use these heads but they said I couldn't run pump gas with them because of the 13:1 compression. They have been ported and polished, and have bronze guides. They also have been modified for the bigger Chevy valves. I also was questioning the date code, the 4M21, would that mean they were actually built January 65? Sorry for these questions, but this is my first restoration and build. Thank You guys for taking the time to reply!!

kalli

ya, 13:1 on what bottom end? ignore that statement. does not make any sense.
i wouldn't want that high compression anyway

what size valves? to make sure they are not hitting stock 289 piston.
have the exhaust ports been ported?

2+2GT

4M21 is December 21, 1964.

The Chevy valves have no effect on compression.

Unless they decked the block all the way to the water jacket, you don't have 13:1.

Pity about the bronze guides. Cast iron is superior. They'll run OK, though, porting and polishing, probably overkill, but 289 heads really gain from this.

Use flat-top or dish-top pistons (the latter if you want to run regular gas) and you should be fine. They'll have to be clearanced, due to the decking. As above, 13:1 is only seen with pop-up pistons. Stay away from them.

TexasAxMan

I'd question a shop that told you the heads would give you 13:1, compression ratio can't be determined without knowing the piston type, gasket thickness, deck height, etc.