An Exhaustive Study in Passing Gas Part I

The first thing that most people do to their stock C5s as soon as they come home is to add an aftermarket cat-back exhaust system. Stock C5 Corvettes, for all of their impressive capabilities, are rather understated as world-class sports cars go, especially with their wimpy-sounding exhaust. Looks-wise, as well, the 2000 and earlier C5 exhaust tips are about as blah, if not downright ugly, as can be due to their funky plain black finish.

Replacing the stock exhaust is exactly where we started when we picked up our new project car, Tabula Rossa, a bone-stock, moderately low-miles Torch Red '99 C5 hardtop. Before we even got the Vette home to California from its former home in Texas, we stopped by B&B Performance Exhaust in Phoenix to try out their latest product, a set of Bullet cat-back pipes. The Bullet system is everything the stock cat-backs aren't--stylish, attractive, and aggressive. They are made entirely of mandrel-bent T-304 stainless steel, with polished 4-inch double-walled tips, weigh within 5 lbs of a Z06's titanium cat-back system, bolt up like a factory system with no modifications necessary, and sound as forceful as a Torch Red Corvette ought to.

The Bullet system eliminates the stock-style side-loaded mufflers for a pair of relatively small resonators, one in each pipe as they come down over the rear crossmember. The Bullet system creates a very pleasant, impressively deep rumble at idle, and a nearly unrestricted roar at WOT. While coming up with horsepower figures on the B&B in-house Dynojet chassis dyno, we also used our handheld decibel meter to measure the volume out the tail. Standing 20 feet behind the Vette, with our decibel meter held flat at waist level, the stock mufflers topped out at 100 decibels at WOT. The same test with the Bullet cat-backs produced a thunderous 118 decibels. It is not unpleasantly loud inside the cockpit, but naturally an aggressive system like this is not for the faint of heart.

While we were at the B&B facilities, we also 86'd the stock LS1 exhaust manifolds in favor of a set of their stainless-steel shorty C5 headers. While the 1.75-inch primary tubes improve the airflow and performance, the shorty headers also look classier under the hood and cut a good 10 lbs off the stock cast manifolds. They bolt right up to the stock H-pipes, as well, and are 50-state smog legal.

We did dyno testing after adding the Bullet cat-backs, and then again after adding the stainless shorty headers. Due to time limitations, we could not give the ECM a chance to run and adapt to each of the changes before making our dyno runs. We simply drove the '99 from the R&D room where we performed the installation, to the dyno room, one door over. Still, we measured a gain of 10 rwhp and 9 rwlb-ft torque from the Bullet system alone, and another 6 rwhp and 7 rwlb-ft torque with the addition of the headers, while still running through the stock catalytic converters. While not measured, we did notice better throttle response during the drive on to California, as the computer adapted itself.

That is all that is required to drop the left-side muffler from the car. Eric carefully maneuvers the one-piece rear pipe's hump over and around the rear crossmember, pulls it free, and sets it aside.	The Bullet cat-back is comprised of two-piece pipes, as opposed to the factory one-piece hump, which makes for an easier installation. The slightly fatter portion of the pipe that Eric is gripping is the left-side resonator, all that muffles the exhaust out of the Bullet. He bolts it up to the factory H-pipe.	Eric pulls the muffler hanger off the stock muffler and slips it onto the bracket of the Bullet exhaust tips.
Then he holds the Bullet tips in place as he inserts and finger-tightens the muffler hanger bolts.	Eric inserts the supplied gasket between the left-side resonator pipe and the tips, before inserting and tightening the supplied bolts to complete the cat-back unit.	This is a rather dramatic comparison between the stock right-side muffler and rear pipe versus the left-side Bullet. Looks alone--let alone weight savings, performance, and sound--are enough to justify this swap.
Eric follows the same steps as before to remove the right-side muffler.	Once the second resonator pipe is bolted in place, Eric can reattach the stabilizer bar to the rear crossmember. The left- and right-side stabilizer bar clamps are attached to the crossmember by two bolts apiece, tightened to 40 lb-ft.	Once both exhaust tips are attached, before tightening the muffler hanger bolts on either side, Eric ensures that the quad tips are resting level to one another. When he is satisfied, he tightens up the hanger bolts.
The B&B Bullet cat-back exhaust is now complete. B&B describes this system as their "deepest sounding C5 system," and they aren't kidding! While not loud at idle, even there it has a very strong, distinctive sound that was sorely missing from the stock mufflers. They look quite aggressive as well.	After dyno-testing the Bullet cat-back system, we let the '99 cool back down, then proceeded to install B&B's stainless shorty headers.	Eric removes the flange bolts from the takedown pipe to the manifold on each side, then removes the heated O2 sensor from each manifold.
From the top side, Eric removes the battery isolating shroud, the fuel rail covers, and the coil packs to allow access to the exhaust manifolds. On the left side, he removes the alternator from its bracket, as well. Then he unbolts the manifolds and pulls them free.	Before discarding the stock exhaust manifolds, Eric very carefully pries the flange out of the manifold collectors to reuse on the new headers.	Then he uses a plastic mallet to carefully tap the flange fittings firmly in place in the B&B headers.
With that, he is ready to drop the new stainless-steel shorty headers onto the LS1.	Because the quality of the metal factory gasket is very difficult to improve upon, Eric inspects the stock gaskets for any signs of wear or damage, and finding no flaws, reuses them with the new headers. He applies anti-seize compound to each of the header bolts before threading them into the block.	The oil dipstick mounts up against the right-side header, and because the contours and clearance of the B&B headers vary slightly from the stock manifolds, Eric must grind off a small portion of the dip stick bracket to fit the new header.
Here is the right-side header after Eric finishes getting it attached to the motor and is done reassembling the passenger side components. The stainless headers look much classier and more purposeful than the cast manifolds used by GM.	Underneath the C5 again, Eric loosens the forward exhaust hanger bolts from the takedown pipe bracket, and uses a wrench as a spacer to provide him with wriggle room to attach the header flanges to the cat-pipes.	Once the three flange bolts for each header are tightened to the takedown pipes on the H-pipe, Eric applies anti-seize compound to the threads of the heated O2 sensors, and screws them into the bung on top of each header to complete the installation.
With both the headers and the Bullet cat-back on, we put the '99 back on the B&B Dynojet chassis dyno, where we measured a solid 16 hp improvement and 16 additional lb-ft of torque at the rear wheels. That is without even letting the ECM adapt to the freer flow of exhaust, and our highly-calibrated seat-of-the-pants accelerometer noticed a further pickup in performance over the following 350 miles.