gt40p users in here please

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Founding Member
May 19, 2002
Its not the EGR that they have to be drilled for its the smog system that they need to be drilled for. I would talk to a machine shop about having them drilled for the smog ports.


the guy who hits on his mom
15 Year Member
Oct 3, 2003
Dallas, TX
The only holes you would need, IF you decide to keep the smog is the holes in the back of the heads. The heads already have the coolant passages stock...

Honestly it'd be a pain in the ass to get the heads drilled, especially since it doesn't really sound like you know what your looking at, no offense.

Either forget the holes and ditch the smog, or get gt40 heads, and forget about egr with the heads, the only time youll have to worry about the egr is if your going to be getting an explorer intake, not the heads.


New Member
Jul 9, 2006
ok, so your saying the gt40p heads come with the egr ports for use with internal egr systems such as the ones on 87-93 mustangs but not the thermactor holes for the smog pump. Thanks


Active Member
Jul 3, 2003

the egr port on ford heads is that port directly in the middle of the head on the intake side of each head. that port goes clear back to the exhaust valve, that's where the exhaust gases come from. as far as egr that's all you need on the heads.

If you're running the p heads, I'm not sure what intake you have. if it's an explorer intake, be sure it's the egr legal intake (96 and early 97) or your egr wont' work. if you're running a stock intake with those p heads, better think about porting it or upgrading, as it's going to bottleneck you bigtime.

as for the holes in the back, don't bother. In fact, it has no internal passages either for the bypass tubing in back, so having a machine shop drill those would do nothing.

ALL those holes in the back do is route fresh smog pump air into the heads when the engine is cold. That air goes straight through the head and out the headers and goes past the o2's. that fresh air tricks the o2 sensors into thinking the motor is running lean, so it richens the mixture up just while the motor is cold. when the motor warms up, the air bypass straight to the cats, and doesn't go through the heads any longer.

since you don't smog test while cold, that tubing does absolutely nothing for your emissions during a smog check. the worst case scenerio you'd have to worry about is passing the visual, for that, and even then you'd have to have a VERY ford savy tech to spot them missing. I just ran tubing straight from the smog pump to the cats and avoided the heads altogether on my p heads. If you must pass visual, jbweld, use a big magnet, your creativity and make it "look" as if the bypass tubing is really connected to the back of the heads, and that's all you'll have to worry about.


Jul 27, 2004
Tucson, AZ
I have GT40P's and I did NOT drill them for the Smog crap, I put everything in like it was though for the visual inspection. I'll be taking my car for the emissions test this weekend.. but I agree with v8only in that it only dumps fresh air in when the engine is cold