Sound Effectiveness of Catalytic Converters
 

Looking to complete my exhaust setup within' the coming year.

Plans are:
Headers - Tomei or JDL Catless UEL
Overpipe/Frontpipe - 3" JDL OP/FP Combo
Catback - Perrin 3" resonated

I'm planning on staying 3" because my plans are going F.I down the road but I also don't want to be boomin' down the streets tuned NA.

With the header being catless and keeping the 3" system a must(YOLO), the only way to reduce sound then is in the front pipe. With JDL being the only 3" offering I know of, there's double resonated or Cat/Resonator option.

Question is, how effective is a catalytic converter compared to a resonator in terms of sound dampening? And would an expensive 300 cell catalytic converter be more effective at lowering the sound than the cheap 200 cell?

I know there are different grades of catalytic converters i.e, cheap Magnaflow vs expensive Vibrant GESI ones rated for 350-500whp. I'm leaning towards Cat/Resonator due to not wanting to smell like gasoline and choking on fumes under a bridge. No straight pipin' here.

Sorry for the long post folks... Really trying to sort this out. Any help is much appreciated! I'm contacting JDL to see the cost of adding a GESI catalytic converter in hopes of more sound dampening with the setup listed.

I am not sure you will find many people with first hand experience of the same front pipe in with the different cat variations. I can say I have the JDL "ultra quiet" front pipe with the GESI cat and the resonated Perrin catback in 2.5" on my car and I am VERY happy with the sound. As always YMMV. I recommend you run a cat for the smell but also the environment, there may be plenty of other things that are worse polluters but every little bit helps.

It's my understanding that none of the aftermarket "quiet" frontpipe options will keep the exhaust anywhere near as quiet as the stock frontpipe, which will still get loud with a catless header and catback. I don't believe resonators will do anything to reduce the volume of your setup and are installed to negate drone.

I feel like your best option would be to leave the stock front pipe in until you go FI. I don't have firsthand experience with the Perrin catback, but based on my time with the Invidia N1 and Tanabe Concept G, I have a feeling that even going to a high flow cat could bump you up into volume levels you won't be happy with. You won't see any significant increase in performance going to a 3" frontpipe before then and the extra work at the time of your FI build will be negligible.

I say save the money it would take to buy all of those exhaust parts and go FI and then buy them. 3" will be very loud if your dont have a turbo. But a ultra quiet and perrin resonated with muffler shouldn't be too loud if the header has a cat.

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Cats muffle sound. Resonators do not reduce noise in terms of DBs. Resonators technically MAKE noise - its just that they are making the inverse noise of a particular frequency so it it feels like it eliminates that frequency. By eliminating some of the "raspy" frequencies and noises, it effectively makes the exhaust sound quieter. A cat is a straight up restriction in the exhaust pipe that has a similar effect to a muffler in terms of physically dampening sound.

if your car is too loud without a cat, the resonator isn't going to make it quieter, just less raspy and possibly limiting drone depending on the frequency.

My old college roommate deleted his cat with no other exhaust mods and the rasp was insane.

I have a samruai with an sr20 turbo in it, 3 inch all the way, two straight thru vibrant mufflers and its nice and quite.
My BRZ has 80mm tomei ti, 3 inch over and its very loud twice as loud as the sr.

I installed a vibrant titanuim muffler which helped a bunch. But the turbo is much smaller on the sr gt28 vs gt42 which absorbs some of the sound. FA20 are loud.

You don't need 3" to go FI.

I make a turbocharged 450hp on the stock front pipe, and paired with a CSG Touring 86, have an in-car cruise volume quieter than a stock car.

Think of catalytic converters as functional resonators.

Stock is effective because the stock catalytic converter is HUGE volume-wise compared with aftermarket high flow catalytic converters.

Aftermarket HFC might not be as effective because most vendors source the HFC from the same handful of makers, so they use standard sized 200 or 300 cell HFC. The HFC is universal so they make it as small as possible to fit a wide variety of applications.

The only time a HFC is as good as stock in terms of sound suppression is when it's large, see the ones used on Apexi/HKS/Fujitsubo for comparison.

I had pretty much that exact setup. I was running a JDL catless uel header, a 3" JDL dual resonated fp/op combo, and a Perrin 3" resonated catback. To be honest it was too loud for my taste NA. The sound was a little raspy and it was loud, but the smell wasn't too bad. I only ran that setup for a couple weeks before putting a turbo on though.

If you're going turbo soon I'd recommend the dual res, my car sounds perfect with the turbo. If you're staying NA for a while, either go with the cat/res or just stick with the stock.

If you stuff a cat in your exhaust pipe it will definitely quiet it down... exhaust and the cat

Hmm I think I'll go piece by piece starting with headers and tune to see when adding certain parts start to become intolerable. I'm not as worried about volume but drone is definitely the thing I want to avoid the most.

F.I won't be happening until a couple of years down the line when paid off and warranties expired. I'm still trying to enjoy the car NA for what it is capable of providing.

Lol!!! Do you really need a turbo?

Nobody even *needs* a car!