5.0 heads...


Active Member
Nov 16, 2004
San Antonio, TX
Hello! I'm considering purchasing some stock '91 Mustang heads for my '66 302 that is undergoing the EFI conversion process. It's an '80 block, with '78 heads, 8.9:1 compression, slightly mild unknown cam specs, L/T headers, and I'm curious as to your opinion whether or not I should purchase these '91 heads from someone I know for $200 - is their asking price.

Does anyone have any #'s I could use for these, so I could plug them into the desktop dyno just to get a feel if there would be any potential or whatnot? Such as valve specs and cyl head cc? I don't want to spend $200 if it's not going to be worth it at all. Maybe I can have them P&P and add roller rockers? I'm also curious to know if I could still use my current headers? Any information on this?
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Depends. I have run 78, 79, and 94 iron Gt40 heads on a 78 and a 68 block. If the price is ready to run, probably not a bad deal. If you have to do a valve job, buy springs, or stuff, I would pass. They are better than the D80E's or 70 cc chamber heads you have, but can easily suck up enough money to pay for serious heads. They have the same 1.78/1.48 valves you have now, with about 64 cc chambers, I think.

If it takes an $250 in valve job costs, $200 in springs, retainers, and milling, etc, plus the gaskets, it may not be worth it, you are at about $600, just to get them on.

The headers, etc, will fit fine.

The iron Gt40's were a great improvement over the D80E's that I had.

One option would be the Thumper versions of that head, with the porting done.
"you have the heads for 200 and ill just give you the fuel regulator, and intaketube and filter. The heads are stock.. should be complete they have the stock rocker arms..you could get some roller rockers..1.6s I think that would work fine."

I'll ask if they need milling or anything. So these are GT40 iron heads that came out of a '91 Mustang? Also, going from 70cc to 64cc would raise my compression a little - say 9.2:1 or so and give me more HP? I'm trying to learn all this information about heads, and it's sure taking awhile.