So there you are at the cruise-in with your polished and pristine Pontiac, enjoying the day and the company of other hobbyists. Your late-model has spirited power and the looks only Pontiac can deliver, but when lined up with all the other beautiful machines, you can't help but wish it had that extra something that makes people stand up and take notice. Then you hear a guttural growl; it causes conversations to trail off and heads to rotate to get a glimpse of what thing wicked this way comes. As it rumbles by, the vehicle appears not unlike your own, but somehow it boasts a totally different personality. You stand within earshot and are almost knocked over by the irony. The car is the same year, model and color as yours, but no heads turned to acknowledge your entrance! As the owner basks in the limelight and responds to questions, insult is heaped upon the injury as he reports the car is virtually stock except for an after-cat exhaust.
It occurs to you that perhaps it's time you learned more about this subject, so here's your opportunity!
The automotive aftermarket has published many reports on the most popular purchases. Number one is usually a set of custom wheels to visually separate your car from the masses of rolling toasters, the daily appliances that get most people to and from their dreary jobs. However, an upstart number two is a kit to legally convert your bland, common stock exhaust system into a growling auditory warning that signals your Pontiac is a wolf among sheep. The rising popularity of these after-cat kits speaks for itself, with ever-increasing numbers of manufacturers looking to differentiate themselves from their competitors.
From its inception, the bolt-on after-cat exhaust made perfect sense in it's simplicity, effectiveness, and marketability. On modern fuel-injected and smog-inspected Pontiacs, many states hit you with an emissions law violation if a properly functioning catalytic converter is tampered with or removed, but anything after the catalytic converter is fair game. Early catalyst-equipped cars suffered significant power losses due to remarkably heavy and restrictive catalytic converters, but this is no longer true. The '96-and-later Trans Ams and the new GTOs were delivered with dual high-flow catalytic converters, which pose little restriction.
However, federal noise regulations effectively saddle these cars with restrictive mufflers, making it pointless from a manufacturing standpoint to spend extra money on high-flow pipes leading to bottleneck mufflers. Although gains can be had from improving flow forward of the catalytic converters, it's simpler and more cost effective to replace the stock muffler and pipes with larger diameter mandrel-bent tubing and a high-flow muffler. These modifications have shown performance improvements in the range of 12 to 20 hp, and some owners report significantly better increases if the vehicle is also equipped with a cold-air intake and skilled computer tuning.
A great benefit for the garage gearhead is that these systems can be affordably mass-produced and boxed unassembled for shipping to almost anywhere. Although they add power and might just kick in an MPG or two for good measure, the huge majority of after-cat buyers make their purchases based on the improvement in sound. No self-respecting hot rod should sound like a Hoover vacuum, so many choose to make a bolder statement. Most after-cat exhaust manufacturers offer different sound levels for you to choose from. There are also many options dependent on how much airflow your combination requires.
The number of kits available is impressive, but the useful information on them is a bit lacking. HPP made a serious effort to give our readership the most important highlights for you to choose what you really want for your Pontiac. Most of the manufacturer's systems are similar in layout to the OEM exhaust but feature larger diameters and much less restrictive mufflers.
Many manufacturers employ the tried-and-true, fiberglass-packed-style mufflers, using either a perforated or a louvered core wrapped with some type of packing material to absorb sound. Several others have developed different versions of noise canceling technology in their mufflers. This style usually employs some type of echo chamber tuned to reflect sound back into the oncoming sound pulses at a certain wavelength, canceling out certain sound frequencies and minimizing backpressure. Other features include different grades of stainless steel construction or the less expensive aluminized steel, various tip styles to provide a custom look, and some have different exit points for a few models.