Emissions GT40 vs GT40P

mine have them, not sure about the P's.

i'm in the same boat with you, and I live in so cal, land of smog checks.

the gt40 heads ARE drilled for internal smog tube passages, the p's are NOT. Plain and simple. You'll NEVER get a crossover tube to functionally work on a set of gt40p heads.

Understanding that, it doesn't make a huge difference. the sole responsibility of that crossover tube on the back of the heads is to pump fresh air from the smog pump into the heads. It does this, however ONLY when the engine is cold. Once the engine warms up, air is diverted into the cats, and no longer runs into the heads. (that's what all those ugly nasty looking piping is for)

anyhow, since you never smog your engine cold, this crossover tubing does absolutely NOTHING for the smog test> I further verified this when taking my 186k 86 mustang stock longblock apart. the holes in the back of the heads, and the holes in the crossover tubes were 100% blocked off, and I had JUST passed a cali smog test before ripping it apart.

It depends how anal you are on this situation. So long as you can make it look functional (stick it on with magnets?) and pass the visual for that tubing (if they even look for it) that's all you should worry about.

You know, this makes me wonder, and I'm guessing you're talking about the inner passages as well too not existing, but I theorize the truck gt40 heads don't have them, but the mustang gt40 heads did. My bro has a 96 explorer engine with the gt40's that he is building, and there is no hole drilled for the crossover tube on the back. We however, were guessing that there were inner passages (as I was told there were, at least so I thought) Now I wonder if his heads are like yours, since they're truck engines.

However, you should have the egr stuff in the center, so, it's just the bypass stuff that won't work on your car (again, a visual emissions thing, and possibly easy to get around)

That does kinda blow doesn't it?!! So many little things like this you and I find on the way that kills the project.

v8only said:

You know, this makes me wonder, and I'm guessing you're talking about the inner passages as well too not existing, but I theorize the truck gt40 heads don't have them, but the mustang gt40 heads did. My bro has a 96 explorer engine with the gt40's that he is building, and there is no hole drilled for the crossover tube on the back. We however, were guessing that there were inner passages (as I was told there were, at least so I thought) Now I wonder if his heads are like yours, since they're truck engines.
.

Click to expand...

Trucks and cars have different emissions requirements which is why the GT40Ps didn't have the termactors passages, and why the particular pari of thermactorless GT40s that Thumper had didn't have them. The only reason the smog pump is diverted to the heads during the cold start is so the cats can warm up quicker and do their job.

Tim

i had my P's drilled and tapped for smog. i live in cali. the guy who did mine did all of central coast mustang's. looking at them it doesnt seem to be that big of a deal. they are still bare if anyone wants pics.

sure, I'd like pics. Did he drill the passages all the way through, or just so that the bypass would bolt up?

These aren't marine GT40's are they? BIG combustion chambers (70cc or something like that). I'm pretty sure all GT40 heads for passenger cars have the passages. Hummm...