Alright fella's here are a few questions that I'd like to find answers to. Which muffler is best? The quietest? You see, I'd like to upgrade my exhause system, but I dont want to wake up my neighbors when I come home at night. Which will increase performance, and kinda keep it to a low rumble? Will Glasspacks help, make better or worse? What's the deal with Bored out Cats? Illegal, legal? Does anyone sell performance Cats? Is there anything that I can do to mine to improve performance/backpressure? Let me know what you know. thanks.

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1988 Firebird Formula 305 TBI, T-Tops, RED.
Of course ... 5-Speed

 

Cossflow muffler tend to be the quietest(IMO) but are also the most restrictive. Most aftermarket mufflers for thirdgen's are crossflows(an exit pipe on each side of the muffler). Chambered(Flowmaster or Hooker) tend to be little more pronounced, but not annoying at low engine speeds. Straight through designs(Borla and SLP) tend to be even less retrictive, at the expense of a distinct low rumble. Glasspacks are annoying to begin with and only get worse with age, and offer no improvement in flow.

I have a Flowmaster muffler on one car, and a Borla on the other. Neither one is loud enough to disturb the neighbours when I start them in the morning. I prefer the Borla because it has a deeper bass rumble to it. If you buy the full Borla catback(which unfortunately costs $500+) you get a cut out for the passenger side pipes, which lets you adjust the tone and volume. Or you can do what I did: buy just the muffler and driver's side tips($229 at CarParts.com) and fab the passenger side cutout yourself(though a set of matching "Intercooler" tips for the passenger side will set you back another $140).

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He who hesitates,... is lost!

 

If you have to pass the sniffer in NJ(?) you will need a functioning cat(including AIR). Get a high-flow cat from RandomTech, Catco or DynoMax.

If you don't have the sniffer but have to pass visual, find a large cat(like from a Tahoe or anything with the 454), gut it, and pass a stright pipe through it. You'll have to do this yourself or get a friend to do it, as the muffler shops can be fined for doing this for you(keep in mind: catalytic's come under Federal jurisdiction - EPA), and most won't even consider doing the work.

If you don't have sniffer or visual, remove the cat and replace it with a straight pipe.

Gutting the cat is the least desirable option, as the sudden opening and closing will create increased restriction and the increased surface area will cool the exhaust very quickly(lost heat = lost velocity). In the end you will probably create as much, or more backpressure, as a properly functioning high-performance cat.

At any rate, removing or gutting the cat is a Federal offence, but it seems left to the individual states to enforce it. Replacing the cat is legal if the cat is: damaged, malfuntioning(clogged) or more than 10 years old.

hopefully I got all my info right on this, but if someone knows better, please feel free to correct me.

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He who hesitates,... is lost!

 

Thanks IROC for your information. It is greatly appreciated.

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1988 Firebird Formula 305 TBI, T-Tops, RED.
Of course ... 5-Speed

 

Your welcome. Living in Canada, I'm not absolutely positive on my comments, regarding the legality of cat removal/replacement south of 49. I have read the EPA "guidelines" regarding the subject but by no means claim to be an authority on it.

"If in doubt, check it out."

I have relaced the complete exhausts on both of my IROC's. Even though there are no requirements in my province to retain the cat's, I put high flow cats on both of them. The power loss is supposed to be around 5 hp, which I figure is a small - almost inconsequential - price to pay.

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He who hesitates,... is lost!

 

Why does a High-Flow Cats cause a HP loss? Wouldn't free'er flow cause HP GAIN? If the high flow cats do cause a HP loss, why do people put them on? Sound better? Someone fill me in Please!

Thanks.

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1988 Firebird Formula 305 TBI, T-Tops, RED.
Of course ... 5-Speed

 

You may have misunderstood me,...

A high-flow cat will cause a power loss relative to a cat-less system. It will still cause less of a restriction than the stock cat, and thus cause less power loss than that arrangement.

Mind ya, GM has gotten better at designing cat's(after thirty years, you'd think they would) and some of the cat's they are putting on current models actually outflow high-flow aftermarket cat's. In a recent magazine article comparing flow of OEM and aftermarket cat's, the unit from the '98 Tahoe actually ouflowed all others. I haven't checked the dimensions or cost of that cat, but it is food for thought if you are contemplating a complete exhaust upgrade.

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He who hesitates,... is lost!