I put my h-pipe on my 85 i dont have any o2 sensors can some one tell me what size of bolt to screw in where the o2 sensor goes so i can block it off thanks for the help

 

Not sure the thread but a 13/16 spark plug will screw right in, you could use that to figure out the threads

 

When I put an aftermarket h-pipe on my 85. I took an O2 sensor to the Auto parts store and found a plug with the same thread and bought them. Kinda looks like a big oil pan plug. Or try the spark plug like the above poster said. I had to put thread locker on the threads because one backed out on me once.

 

wont that kill ur gas mileage?????

 

from what i've seen on my H pipe, the 2 ports are blocked off and I still manage about 220 miles per tank. Not driving like grandma all the time either

 

Go to the harware store and go to the automotive department and they sell them there, just put two in your pocket and walk out. Ace is the place for a smile on my face

 

There are no O2 sensors on 85 GT's. And they didn't come with true dual exhaust in 85 so if you want to put dual exhaust on an 85 or older you have to put an exhaust from an 86 and up Fox along with changing the trans cross member. And block off the O2 bosses. So no it will not affect your gas mileage.