Ct1987

Hi everyone,
I have a 1987 Formula with the 305 engine and I have removed the cat and associated emission garbage. When I took off the cat the exhaust noise increased. I then installed the wonderful Dyno Don's headers and the noise got more objectionable. I want to lower the noise and drone and and need suggestions. My thought was to place a resonator in the spot the cat was living. I still have the original exhaust system from where the cat was back. Its in perfect condition with only 14 k miles. I would be willing to remove the original exhaust for something more mellow. I want more of a hum than a raspy sound.

What are your thoughts?

Thanks,

Louis

midias

I have had similar issues on a lot of cars. Adding a resonator helps a lot, I would go perforated vs louvered core. You can add it where the cat was.
I used this one worked great really reduced the drone and rasp. I used it again on my friends TA with a flowmaster and it helped a lot when he was cruising
https://www.summitracing.com/parts/wlk-24222

midias

I added it a bit farther back on my friends TA

Whitebird75

Why not install a new cat? it will do the job and your car will not smell like rotten eggs and unburnt gas while setting in traffic.

midias

For my fire bird I don't mind, when the cat died over the summer in my Accord I put in a test pipe. I regret that I need to spend the money on a a new stainless cat make is smell less bad

BovineZro

iTrader: (11)

I second this. I bought a 3" in/out cat for for $95 (MagaFlow 94019, back in 2017 though). A new, modern cat is no more restrictive than a resonator or muffler. Prior to that, the exhaust stink was so bad I wouldn't even start the car in the garage. Had to push it out into the driveway and then start it. Sitting in traffic was awful too, unless there was a good headwind. Sometimes other drivers would roll up their windows when they got close to me. Drove it that way for less than two weeks.

With the cat, the exhaust note was quiet but got more aggressive above 3000RPM or so. Sounded pretty good.

yankeecarman

iTrader: (9)

After my cat failed in my 91 TA in installed a high performance cat and was very pleased with the note and it wasn't too loud.

scooter

iTrader: (11)

Keep adding mufflers until you get the desired effect. I have a Borla cat-back setup in my car, no drone or rasp with the bypass fully blocked

Ct1987

Thanks for the suggestions. Actually my car does not smell at idle. There is absolutely no smell of rotten eggs. I have until spring to make a decision. I have to look at the Borla system. I had that on my 89 jeep and it was great.

Thanks,

Louis

TransamGTA350

iTrader: (2)

Maybe not rotten eggs, but there is definitely more of a stink without a converter. I would put a high flow cat on there and see how you like the sound. From there, change the muffler to suit the sound you want.

Ct1987

Hi Scooter,

What model of Borla exhaust did you get. I just checked their site and they do not have one for the 87-90 Firebird. they do have one for the 84-92 Camaro Z-28.

Louis

scooter

iTrader: (11)

Same car.

https://www.borla.com/products/chevr...t-system-14888

Even comes with different pipes for the beginning of the system depending on what size the cat pipe is. I think it even works for the V6 cars

Ct1987

Thanks Scooter. I really the Borla systems. This will be a spring project.

Louis

QwkTrip

iTrader: (22)

I thought the rotten egg smell was a byproduct of catalytic converters. That smell goes away if you remove the cats, but the exhaust/fuel smell gets stronger.

Modern cats don't hurt power. And they're a great muffler too.

BobWolf

I would check with the inspection station. Federal law states vehicles built after 1975 the cat has to be there to meet federal law. I have failed several inspections on cars missing the cat. Considering properly sized monolithic cats especially updated cats flow without any effect on performance there is no reason not to have one on any car.
Add: Walker makes a good cat that flows great. If your vehicle is mostly stock increase the size no more than 1/2 inch or 13mm so you keep the exhaust velocity, scavenging, and low end torque.