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289 Heads on a 302?
Anyone ever put 289 heads on a 302? The previous owner of my Mach1 said that it has 289 heads in order to take advantage of the smaller compression ratio? Just wondering what the pros and cons are by doing this?
[Image: 1gq8uo.png]
1971 Mach 1 - 306cid/C4 Bright Yellow
1972 Coupe - 306cid/C4 Gold Glow (in restoration phase)
The previous owner was probably referring to the smaller head volume on the 289 versus the larger head volume on the '71 302 motor. This equates to a higher compression ratio for the '71 motor when the 4V 289 heads are used.

With higher compression, you generally get more power. The '71 mustang 302 had a compression ratio of 9.0:1 while the 289 4V head ranged from 9.8:1 - 10.0:1, dependent upon the year.

I have not personally effected this changeover.

Hope this helps.

So it's a good thing! Should make it run better on regular grade gas! I know the guy at Ford Racing said that my new crate motor was a higher compression ratio and could run on regular gas better than the lower compression engines. The crate is 10.0:1 also.
[Image: 1gq8uo.png]
1971 Mach 1 - 306cid/C4 Bright Yellow
1972 Coupe - 306cid/C4 Gold Glow (in restoration phase)
Actually, the higher the compression ratio, the more likely one has to use premium gas.

I do not believe you will normally have a problem running regular gas with 10.0 compression. A lot of other things come into play with the primary one being ignition timing. You can also generally run a bit more compression with aluminum heads than the iron ones.

When the octane ratings begin to drop a couple of decades ago (has it been that long?), many of us went to dual or triple head gaskets to lower our compression ratio in order to run the available gas. Oh, to see the days when you could run 12 to 13 compression ratios without having to use race gasSmile?

Hope this helps.

Good to know! These gassers are kind of new to me! I'm an old diesel dog! LOL
[Image: 1gq8uo.png]
1971 Mach 1 - 306cid/C4 Bright Yellow
1972 Coupe - 306cid/C4 Gold Glow (in restoration phase)
I know my girlfriend has 305 heads on her 350 {aaahhhh chevy talk}Blush But her valves were oversized. It makes sense when you think about it because you might get better compression but you get less air and fuel from the smaller valves.Sometimes a good set of after market heads is a better option especially if your planning on putting roller rockers because then they have to machine the heads. Well at least on Cleavland heads but I'm thinking probably all stock heads.And don't forget that if the 289 heads come off an old engine sometimes the valve guides need changing and the exhaust seats.I know all this because all that work had to be done on my Cleveland heads. All in all it might of been cheaper or at least the same to buy after market heads.I don't mind because my goal was to start with a mostly stock engine and see how much I could get out of it with just a cam change .hahaha far from that now Tongue

[Image: a58hgh.jpg]
I'm gonna say its not worth doing--you might gain some low end but mid and upper will suffer with 289 heads. If your looking for a good/cheap swap try some E7TE (HO) heads from a 1987 to 1995 mustang 5.0
I don't know about the v8's but the on the 300 inline's the favorite upgrade is to stick a 240 head on it in order to raise compression.

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