Emissions GT40 vs GT40P

thumper460

Founding Member
Jul 24, 2000
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Orange Park , Fl
Most guys dont need to even care about Emissions, but there are a few out there that have to go under the Fed Regs all the time!! SOOOoo...

the question is: what heads HAVE the air port in them and will take the air tube?? Some have ... some dont.!! right? Which??

HHhhmmmmmmmmmmmmmmmmmmmm.......................

Just me.......................

Thumper
 
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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.
 
V8only.. rocking!! however.. the reason for this is because I have a set of GT40's ( not P's) with NO air passages!! None... nada... zip!! And that really Sux to the emission car they WERE going to go on!! ( visual and pipe test) SOOOooo.... thanks for the answers... BUT if you have to make the em tests... best LOOK for those Holes befor you buy GT40s that DONT Have them!! Pass this on to the guys... cool??
Just me.............................

Thumper
 
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.
 
Roger that... V8only!! I ran a drill 1 1/2 inches into the bolt hole ( air port normaly) and didnt hit ANY existing hole!! I feel the heads are solid all the way thru!! Also, there is NO threaded hole for the crossover pipe to mount to... so that would have to be mocked up on a block and then drilled to fit the pipe... sux!!

Thanks... I just felt the need to let others know to be carefull IF they have visual to pass also!!

MERRY CHRISTMAS...

Tpr
 
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.
.

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