So my local referree guy says I can put an LS in my Trans Am. We discussed every aspect, then he charged me $30 for his time. Oh well. I showed him pics of the existing headers for this swap, and he said no. Nothing could budge him. His reason was a law about the placement of the catalytic converter(s). This is what we spent the most time on. I can't see using the factory dual-cat setup, but I did get him to agree to letting me use MagnaFlow's high-flow replacement cat for the '87-'88 TPI 350 f-car, in it's correct location, with any quiet-enough-to-be-legal cat-back, and any exhaust manifolds and Y-pipe, including custom-made, that would fit. And I got it in writing. Decent guy. Have any of you tried anything like this? I'm guessing I'll need to start with a pair of '98-'02 Z28 exhaust manifolds?

 

i say go to a different shop and get the exhaust done the way YOU want it, not the way some fab guy wants it to be. just my $.02

 

Well, that's not a muffler shop telling him that, it's a emissions referee letting him know what can and can't be used.

I'm not for sure how hard it will be to use the stock LS1 manifolds on a third gen, I've heard some that have used them, cut off the flanges from a 4th gen y-pipe and had it fabbed up to a y-pipe that would work ok with a single cat, dunno how the PCM will like it though.

 

Klortho is correct. It's this way or no street legality. I'm glad to hear there's rumors of others trying this. Thanks. As for the ECM not liking it, I'm guessing you're referring to possibly choking the exhaust flow? I've found evidence I believe, that a single 3" exhaust will support 350 rwhp (with T56 and drag radials) without restriction. AFAIK, most stock LS1 F-cars with T56 are just under this. I'm hoping that I'll be fine as long as I use a GM LS1 cam and unported LS1 heads.

 

No, not the choking of it, but the fact that the PCM will look for 4 O2 sensors (cut down to two with O2 sims, but then that probably wouldn't be legal where you are) 2 in the manifolds, 2 after the cats, the 4th gen y-pipe is interesting and may actually work in a 3rd gen to where you can keep all the cats on the car just to ensure that nobody raises a stink (no pun intended) about only having one cat on the car.

 

Couldn't you just run 2 cats, like some 3rd gens came with stock?

That would allow you to run all 4 sensors so the ECM would still be happy.

 

Dual cats would work, or just run both rear O2 sensor behind the single cat. The PCM will never know.

The rear O2's are monitor-only, not part of the control system.

Although they might not like the gases they see coming out of a 3rd gen cat.

Biggest problem I see is routing the driver's side pipe over to the stock 3rd gen cat location. There isn't any room between the oil pan and K-member like there is with 3rd gen engines.

 

I always thought though, that the cat forward system had to match the ENGINE, not the chassis. Meaning that the 4th gen placement of the cats was what was required for legality, not chassis placement of the cat(s).

I know here in TX, nobody (that I know of) has had any problems passing, not even in emissions counties.

 

Basically, conflicting requirements. The chassis has to have the cats in the stock location. The powertrain has to have all of the original equipment.

I'd say that's a mistake by the ref. Toss the laundry.

("After further review, the decision in the field has been overturned. The owner will have to run 4th gen cats where no cat has ever gone before. Half the distance to the goal and loss of down.")

 

Thanks everyone! The third gen front subframe tapers, while the fourth gen does not. The dual-cat introduced in 1989 would have the driver's-side exhaust gasses too cooled off by the time they got over to the cat, but the Y allows the hotter gasses from the girlfriend side to warm the cooled gasses somewhat, and to heat the cat up quicker. The cat I settled on is ceramic core, though I'd prefer a stainless steel core, high flow cat, but those are only made up to 2.5", not the 3" I need. I may have to get a custom oil pan to allow the y-pipe to pass under it, or between it and the flexplate. But that has nothing to do with emissions, and is a small price to pay. I'm lucky that less than 100 miles away, there is a nationally-known ceramic coater, famous for doing headers. also less than 100 miles away is a company called dr. Gas, they do exhaust crossovers and have a mandrel bender. New exhaust manifolds would run me $500 with shipping if I can't find any on E-Bay or Craig's List. If Dr. Gas can do me a custom Y-pipe, and I can get it ceramic coated inside and out, I should be able to have high flow and high heat. PLEASE keep the comments coming!

 

hmm i am lookin too dual straight pipes on my swap if i can where i live in florida no one checks emmisions so unless it is something mechanical that won't allow it then i guess it won't happen... glad i live in ******* fl where i don't have to worry much about emmission standards...

 

try this setup. i got the pic here. look on the dual exhaust pic's board.
they look good to me and they route back to the same place as the original ones. if its metal then you can bend it. put on the dual cats and run duals all the way back if you want.

i actually wanted duals but thought what the heck, i will use the 2055 with a 3 inch y pipe all the way and that will be more than enough for street use. i wont win any races, but i wont get mugged by the dmv either.

 

very good pics, thanks for sharing.