I just finished swapping a 87 350 tpi into my 91z28 convert. 305 tpi and I noticed that they were different. The part #'s are different and I measured the outlets and the 91 305 tpi and the were around 2" .The 350tpi were about 2.25". It looked like I could swap them out and use the existing pipes. The flanges had a big enough flare on them it looked like the might work. Does any have info on this? Also I thought all tpi's had the bigger outlets verses the lg4's and Lo3's. Thanks

 

All the 350 TPI's, the L69 HO Carb's, and the 305 TPI's with the G92 performance package got the larger outlet exhaust manifolds. The smaller ones were for low output 305's like the LG4, TBI, and LB9 with single cats.
If you're using the larger y-pipe and i-pipe, you need to put in the larger exhaust manifolds as well so everything matches up and you get the full benefit of your larger exhaust.

 

From what I understand, the '86-'90 TPI manifolds were all the same, whether LB9 or L98. In '91, only the dual-cat LB9's got the "good" stuff.

I could be wrong, as I don't have any except '87 LB9 to actually measure.

 

I have an 87 LB9 with G92 and a single CAT. The stock manifolds are part numbers 14094063 & 14094064 and measure 2.18 & 2.19 inches inside diameter of the manifold outputs that would connect to the pipes.