GT40 Heads

[Eric]

Hello all

I have a set of GT40P heads destine for a 351W. It is my understanding the only thing that needs to be done to make the heads fit is to drill the head-bolt holes out to 1/2" so the larger 351W head bolts will work. Is this correct? Is there anything else of concern?

Thanks.

Eric

[Dave Wood]

If you are referring to the new GT40P heads as opposed to a 1960s set, I believe that they all had the same hole diameter. Somewhere in the mid 80s the 351W and 302/5.0 began using the same heads, so they would have had to use the same diameter holes or it would have required the factory to modify them and that would have likely generated another part #. I imagine they just used flange bolts like Ford sold through the old Muscle Parts program to allow the 351W heads to be used on the 289/302 at the time.

[Eric]

Yes, these are late-model heads.

Eric

[Chris K]

GT40P heads are completely different from GT40 heads "P" heads are straight plug heads and usually have headers that are custom built for that application. I have these on a '65 Mustang w/ upgraded valvetrain, lightly ported, bowl blended w/ custom Tri-y's fitted. They are really nice Iron heads but take a bit to adapt (mainly the headers).

[Eric]

Originally Posted by Chris K

...but take a bit to adapt (mainly the headers).

Thanks, Chris

That's the info I'm after. To use these heads (they are GT40P, not GT40) on a 351W, what needs to be done? Anything other than drill the head-bolt holes larger? It is my understanding that is the only thing that needs to be done. I'm not concerned with the headers at this point, I'll deal with that later.

Eric

[Chris K]

As far as I remember, other than the plug issue you might want to look at the exhaust port shape, for gaskets and port matching to your header flanges, other than that they are after all Ford heads, I cant remember head bolts having to be drilled.

[Eric]

Thanks, Chris

I don't recall where I read that the head-bolt holes need to be drilled for use on a 351W, but I think it might have been in Car Craft or possibly on one of the Ford truck forums (those guys are big into 351W builds). I'll be able to tell you this weekend if it's true; pretty simple test, if the bolt fits, you don't need to drill.

Eric

[Eric]

Just by way of information for anybody searching this topic in the future, the head bolts on a 351W are definitely larger in diameter than the head-bolt mounting holes on the GT40P heads. I just checked to confirm. So, yes, the head-bolt mounting holes on the GT40P heads need to be drilled out larger in order to use the heads on a 351W.

If anybody has done this swap and would like to impart some additional wisdom, please chime in.

Thanks.

Eric

[Jon]

The 351W uses 1/2" bolts and other SBFs use 7/16" bolts. For most aftermarket heads the holes are 1/2" and you use a set of head bolt bushes. As you are using 302 heads on a 351 your going to have to drill the heads to 1/2".