can one if you guys that has a factory 318 truck measure the y pipe diameter on your truck next time you are under there? i got my caliper out and looked and mine in 1 5/8" OD so that is 1 1/2" ID!!! that is and itty bitty y pipe for a v8. but mine came with a v6 so i was wondering if they changed it. is also is crimped on the drivers side and it looks factory. about to have a new 2 1/4" one made with 3" pipe back to the duals and free it up, i think that is why she does not have the upper end power it should cuz that baby exahust is chokeing it up.

 

For mine its 2in OD. I dont know what the wall thickness is so I cant tell you the ID. But if your ID is 1.5 that is not too bad. Just think of 3in is great for a v8. Now 1/2 of that is 1.5 per side of the engine. So your good!