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I am getting ready to rebuild my 289 heads (hardened valve seats etc.)and I noticed some Mustang enthusiasts put 302 heads on 289 blocks. What is the advantage of using 302 heads? I guess I didn't realize they were much different, but I will definately go with the better stuff. This will be a "mildly modified" street car (not a drag car) Is it worth the effort to find some 302 heads?

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It is not an advantage to run stock 302 heads. In most cases it is worse. The reason is that 302, (particularly newer 5.0) heads have larger chambers than 289 heads, thus reducing compression by 1 to 1.5 points.

Aftermarket heads are also tailored to 302 (5.0) engines, thus to maintain you compression, you need to install domed pistons or have the heads milled. The aftermarket heads have much better flow characteristics over stock heads so the performance is greatly increased.

You might want to consider heads done by Powerheads. They are about $800 but are stock castings that have been CNC ported and have had larger valves installed.

Good Luck
 

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If you want to lower your compression ratio, say, if you're using flat-tops (which can give a pretty high CR with 289 heads) and don't want detonation problems, using 302 heads would be a good way to achieve this. The combustion chambers are larger.

Other than that, depending on year of 302, they're essentially the same as what you have. Only major difference I can recall, if you have early 289 heads, is that 302's (and some later 289's) have rail rockers and a large pushrod hole in the head. Early 289's have slotted pushrod holes which guide the pushrod, similar to this HiPo head

I ran 289 heads on the race car in the early years (ported) and achieved good performance (mid 11's) before going to '69 351W heads, which got me into the 11.20's. I never ran 302 heads so I don't have any practical experience to share, other than noting their similiarities from the core engines I purchased.

If you want to look for a "better" set of OEM heads, look for some '69-'70 351W heads....

Good luck!
 
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Because of their smaller combustion chambers, a set of J code 1968 4V 302 heads would be a nice addition to you 289. You could have increased flow, but not loose the compression you would with other 302 heads. Not an easy item to find, but good luck nonetheless!
 
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