GT40 Heads

Hg80Design · Dec 30, 2008

I am looking at adding some GT40 Heads to my 302 not GT40P. Its a 71' 302 block with rail rockers and an aftermarket manifold. I am curious if this is a direct bolt up, will there be any kind of gapping around the manifold? What kind of power gains can be expected from these heads over stock? Any help or advice on this would be greatly appreciated. Also besides being aluminum is there any other advantages to using the GT40X heads?

Decurion · Dec 30, 2008

The X heads have much bigger intake ports, about 185cc, versus the gt40s at about 135ish. If youre looking to stay with an engine thats "stock modified", the gt40 heads are great. The only real drawback is that the non-P heads have large combustion chambers, at about 65cc. The later P heads have smaller 60cc chambers, but the relocated spark plug angle. Rumor has it that the P heads will work with stock exhaust manifolds. If you go with the non-P heads, make sure to mill them .030 to keep compression reasonable, as this is what the 93 Cobras had. A little port work, mostly around the bowl on the intake, and all the way through the exhaust port will really wake up either head. They bolt up like any other head and will give you about 30hp or so over a stock E7.

Hg80Design · Dec 30, 2008

Does any one produce or sell the GT40 heads already set up as a refurbished one or new? Besides using something like ebay, have had bad experiences with them

dbfarr · Dec 30, 2008

This guy may be able to help you, though he really likes to massage e7's

Killer Ported Heads as in MM&FF !! - StangNet Mustang Classifieds

Well known over in 5.0 forums

57fairlane · Jan 1, 2009

I wouldn't bother with gt40 irons unless you can port them yourself or can pick em up for under $300.

The only big difference will be that you need to get a set of pedestal mount rockers . . .

Decurion · Jan 2, 2009

Hg80Design said:
Does any one produce or sell the GT40 heads already set up as a refurbished one or new? Besides using something like ebay, have had bad experiences with them

The local parts store of your choice will have them, if you know what to ask for.

phutch11 · Jan 8, 2009

Don't fool with them unless you can get them really cheap. There is a huge false economy with used heads - after you shave them to get decent compression, drop in a couple new valves, new springs, retainers, new rockers -- pretty soon you could have spent a little more and gotten much better power.

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rbohm · Jan 9, 2009

phutch11 said:
Don't fool with them unless you can get them really cheap. There is a huge false economy with used heads - after you shave them to get decent compression, drop in a couple new valves, new springs, retainers, new rockers -- pretty soon you could have spent a little more and gotten much better power.

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i agree with this statement. better to spend the $800 up front and pick up a new set of windsor jr heads from world products that are complete, bolt on, and have 58cc chambers, than buy a set of used heads for $350-500, and then spend another $350-500 on parts and labor to rebuild the heads and get the compression ratio you want. when equally prepared, the only real advantage of aluminum heads is the lighter weight, and the ability to run slightly higher compression or more ignition lead. otherwise power gains are the same.

65FBE2 · Jan 9, 2009

Actual Iron heads will make more power if everything remains the same. They hold more heat in the cylinder, heat is power! The only reason alum heads make more power on the street is due to the before mentioned added timing and slightly more compression tallorant with pump gas. On race gas iron heads will make more power

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