Hey Thirdgen,

I have two 87 IROC's. both have 305/5spd. I am working on a technically correct factory restoration for the convertible. I want this car to be as close to all original as I can get it without having to refinance my house. I have found what the seller on CL describes as an unused original exhaust. But its just the portion rear of the CAT. I know I'll probably never find an original unused CAT so I will be forced to buy an aftermarket unit. So I have 2 questions. Anybody know which aftermarket CAT is closest to the original? And, I will be reusing the original Y pipe. But it is welded onto the current CAT on the convertible and bolted onto the CAT on my coupe. Which is correct? I suspect bolted on?

Thanks guys.

 

IIRC, the converter on my Camaro is a 3" slip fit onto the "Y" pipe (inlet) and a 4-bolt flange on the outlet.

 

(not my exhaust)

 

It is in fact a two bolt flange. Assembly manual says otherwise.

 

OK, I just read another post that was pretty convincing about the fact that there was never a 3rd gen that came with a 3 inch exhaust. The largest was supposedly 2.75. Unfortunately the post didn't say if there was also smaller pipes (which I assume must be true for the smaller engines?). Does anybody know for certain what size was stock for an 1987 305 with the 5 speed and the G92. I understand this combo came with a slightly beefier cam so perhaps this combo also got the biggest exhaust pipes of 2.75 inches?

 

http://mastercatalog.walkerexhaust.c....asp?img=10394

 

on my 90 5.7, the factory cat-back pipe to the muffler was 3".

 

The 87 Z came with either an LG4 305 (smaller exhaust) or the LB9. Both used a two bolt ball socket connection from converter to intermediate pipe.

Four bolt connection with gaskets was used on the L69.

 

Thanks naf!

good info. Anybody know the actual size of the intermediate pipe. There's one reply here but I'm getting mixed answers outside this forum. I understand that it was NOT a 3". I found an original unused intermediate pipe on CL but it is 2 1/4" and I think that is too small? I'm leaning toward it having been a 2 1/2" intermediate? Anybody know FOR SURE? I know it is a single cat and intermediate pipe not a dual.

Remember, it's a 5.0 with 5spd manual and G92. I believe that means it got the bigger cam and perhaps that has an effect on the size of those pipes?

I've been waiting on putting this phase of my restoration back together because I don't know what pipes to use to be as close to factory correct as I can get.

 

 

In 89-92, 350 and 305 tpi 5speed (performance option) cars got the 2 3/4" intermediate pipe.
Others got a smaller pipe but I have never had any of those cars to know what the size is.

There were 2Y pipes for the V8 cars low and high performance sizes. Then in 89 the dual cat Y pipe came along and also changed how the catback intermediate pipe mounted up and also added a extra 10 hp..

 

Actually three (four counting the dual cat y). LG4 lo-perf-garden hose; L69 with the oval four bolt connection to cat and four-bolt flange connection to intermediate and TPI with round slip fit to cat and two bolt ball socket connection to I pipe.

I am in the process of swapping LG4 exhaust on my 84 to TPI exhaust but do not have access to stock I-pipe. I have the L69 exhaust on my 85, but again no factory I-pipe. The L69 y is certainly larger in diameter than the TPI exhaust and a good bit heftier.