batmanrobinwilliams

I recently got an all-stock 1990 coupe with 50k miles. It has original exhaust up to the mufflers, and I'm looking for ways to improve it in terms of horsepower but not being too loud at cruise and idle. The cats are possibly rusted with being so old, and the plan is to improve the system regardless of rust being present or not. I've read many threads on here talking about this topic, but wanted to get some expert opinions from people who have personally done different options. Below are the options that are being considered, and any advice would be greatly appreciated:

1) Replace precats and main cat with OEM replacements
2) Eliminate precats but replace main cat with magnaflow
3) New precats but eliminate main cat and go with x-pipe
4) Eliminate all cats and go with duals and x-pipe...would this be too loud?

I realize the legal repercussions with removal of cats, but since this will end up being an "off road only" classification for the track, that will not be an issue. Thank you all very much in advance for any of your experience and opinions.

billschroeder5842

I did something similar to my 89 with the L98

Eliminated the pre-cats. Better sound and an immediate P/U in power
Swapped the main Cat for a HiPerf one. Flows much better
Left the stock mufflers in place. They really are pretty good flowing and NO DRONE!!

"True Duals" will be very expensive (relatively speaking) on your car as it was a single exhaust design.

Most people comment that the exhaust sounds great (is does), I noticed a pick up in power and it was only $350 for the whole thing.

batmanrobinwilliams

Awesome! Thank you very much. Did you notice much (if any) of a volume increase when you removed the pre-cats?

billschroeder5842

Yes, the volume was louder as there was a pretty healthy reduction in restriction.

However, I do not find it too loud. Very nice at cruise and Idle.

CRUZN C4

Borla S-Type cat back. Not too loud but an awesome deep tone.

aklim

I really don't think you are going to gain much with the exhaust. Your stock system isn't that bad. What is hurting you is the exhaust manifolds. You can replace them with LT headers that dump into a higher efficiency cat. That would remove the pre-cats and the exhaust manifold restrictions and the ancient cat you have in place. Also you can remove the AIR system and clean up the engine compartment for easier access. What is your budget?

Headers





Y Pipe





Unless you get your exhaust system flowing more the cat back is going to just be there to make "Ricer Sounds" for the most part.

batmanrobinwilliams

I currently have Borla S-type mufflers on there but am switching to Corsa Sport that I already have. The mufflers are not what I am looking to change, but rather everything upstream from the mufflers. The LT1 setup will fit okay? I'd rather not mess with changing the headers right now just to avoid the hassle. Budget is around $350.

aklim

I really don't see the "bang for the buck" gains unless you are making a huge amount of power if you are not doing headers. Personally I HATE my Borla system for being too noisy. I'm willing to sacrifice some of the refined levels of noise for some gains on the dyno. That said, I think the Borla is a better system if I were looking for a loud noise to impress the ricer crowd.

People have reported better noise abatement with the LT1 and even better with the Corsa. What I am unsure of is if the stock is more restricted than the Corsa and how much better the Corsa is. And also what to do with the Borla if I get something else.

batmanrobinwilliams

aklim

You could replace the cats with higher flow ones. I didn't myself because the pre-cats were gone with the TPIS and the main cat was hollowed out. It made more noise than the wife liked so I put in a main cat with a Random Technologies one (which they don't make anymore) and it kept it somewhat respectable enough for her to be in it without her grumbling.

A magnaflow main cat is already $170 so that is half your budget.

For the pre-cat, probably THIS which comes to about $305.

Before I worry about them being clogged or rusted, it might be cheaper to drill a couple of holes and check the back pressure so you know before you drop down $500 to change something that is bad. If it was $50, go for it. That should keep down the noise and increase the flow ASSUMING that it is clogged and that isn't established yet.