Hey guys,

I'm looking for a cheap cylinder head upgrade for the 351 Windsor that I'm building later this spring. I want to junk the original cylinder heads in favor of some GT-40 or GT-40P cylinder heads off the 302 explorers.

I've heard that the GT-40P cylinder heads (late 1997 explorers and up) are better than the 1995-1997 GT-40 cylinder heads. I've also heard that the only modification that needs to be made is to enlarge the bolt holes on the block to 1/2". I do believe I can still use the 351 Windsor intake manifold, but I'm still looking for more info. on that. What about valve train geometry, does that change at all?

Has anyone here done the swap, or know anything else about this swap? I'm also looking for the combustion chamber volumes for the 1974 351 Windsors.

Thanks guys

With the GT40 heads, it's as simple as getting the bolt holes bored out. With the GT40P heads, you'll have to get the bolt holes bored out and make some mods to the headers so as to not burn up your plug wires.

Bob said:

With the GT40 heads, it's as simple as getting the bolt holes bored out. With the GT40P heads, you'll have to get the bolt holes bored out and make some mods to the headers so as to not burn up your plug wires.

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Thanks for your input. Do the plug wire boots ride up against the headers, or very close causing burnt wires? I know a few companies make special headers for the 351W + GT-40P heads as well... I was thinking that maybe a ceramic coated set with a thermo exhaust wrap would do the trick...

and i think gt40's ar better then gt40p's

F 150Cobra said:

and i think gt40's ar better then gt40p's

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The GT-40P heads have a slightly higher CFM rating then the GT-40. I just read that the difference wasn't very noticeable, and a lot of guys went with the GT-40 so they didn't have to worry about the spark plug angle and header fitment. I could always have the GT-40's ported, but I'm trying to keep the costs down, hence the GT-40P's

I can't find my notes at the moment, but if memory serves, the #4 and #8 plug holes are almost directly behind the headers on the GT40P heads. Don't quote me on that though, as I can't find my notes.

I'm sure Paul will eventually find this thread and can shed some more info about it. Here's a link he posted for me concerning the heads.

http://farm4.static.flickr.com/3048/2349350691_b48f448e3d.jpg?v=0

Bob said:

I can't find my notes at the moment, but if memory serves, the #4 and #8 plug holes are almost directly behind the headers on the GT40P heads. Don't quote me on that though, as I can't find my notes.

I'm sure Paul will eventually find this thread and can shed some more info about it. Here's a link he posted for me concerning the heads.

http://farm4.static.flickr.com/3048/2349350691_b48f448e3d.jpg?v=0

Click to expand...

Yea thats tricky...Should be able to work through it though..

Thanks for the information sheet on the heads, just what I was looking for.

The P heads flow a little better than the regular GT40, but just a little.. you could get more from the GT heads with a little porting, so it's your call if the header issue is worth the trouble or not. The 351 responds to airflow increases across the powerband all the way up to the AFR185 level so take what you can get, after that the powerband begins to shift up the tachmeter.

conanski said:

The P heads flow a little better than the regular GT40, but just a little.. you could get more from the GT heads with a little porting, so it's your call if the header issue is worth the trouble or not. The 351 responds to airflow increases across the powerband all the way up to the AFR185 level so take what you can get, after that the powerband begins to shift up the tachmeter.

Click to expand...

Thanks for the info.

I'll talk to my machinist and see what kind of prices I can get the heads ported for. Who knows, with the exhaust dilemma, it might almost be cheaper to have the GT-40 heads ported. This way I can get even more flow than the GT-40P head... Though I will loose a little compression with the GT-40's, but that depends on my piston selection... I want to run 92-93 Octane fuel...

Just have the GT40 heads shaved down a little, that will reduce combustion chamber size.

Sounds good, I will just have to save my pennies and have the work done to the GT-40's

I noticed that the exhaust valves on the GT-40P heads were 0.08" smaller than those on the GT-40 head. What effect will that have on my performance with the GT-40 head VS.The GT-40P head?

Yes the P heads have a slightly smaller exhaust valve, but the ports are a better design so all together they actually flow more air. Porting the GT40 heads will make up this difference and then some, a competent porter should be able to get 20-30cfm more on both sides.

Sounds like a plan, thanks for your help