I have a set of Gt40p heads and a noticed that they dont have the smog pump ports ont he back of the heads. i heard you can tap the head with a 5/8 tap 11 threads per inch. If i were to do this, would there be any problems when i hook up the smog pump?
The holes in the GT40P heads don't line up with the holes on the AIR tube setup. In my area we only have to pass a visual so I just drilled the AIR crossover tube so I could just bolt it to the back of the heads. It's not actually doing anything.
The smog nazis wont know the difference between E7s and GT40Ps and as long as the AIR tube to the back of the head is present, they wont care. GT40Ps should actually burn cleaner then the stock heads anyways.
When I installed mine in 2005, I found a company in Indiana that actually sold the heads with the passages drilled out and everything was supposed to line up. Instead of going with them, I just got a stock set of P's and simply left the air tube off the heads. I ran the air tube directly from the smog pump to the cats eliminating the bypass valve. It looks stock and given the lack of preheaters on my 2 cat pipe, I don't think it made any difference.