1999 Corvette Exhaust System - Totally Exhausted

Living here in the good ol' USA, we have options-too many as far as I'm concerned. one can choose where they want to live, what they want to live in, and for a little extra-oK a lot extra-what kind of amenities they would like. I remember as a child drinking water from the tap-yes, we actually used a glass and drank the same water as our fellow neighbors. Now we have an abundance of plain bottled water, flavored water, and vitamin-enhanced water to choose from. Talk about a spoiled society.

Well, there's no turning back now and the automobile is no exception. When purchasing a new-model vehicle, one has many choices: Do you go with the 4-, 6-, or 8-cylinder engine? If you choose the 8-cylinder, do you buy the standard or the high-horsepower version? Many options can be had depending on your budget. Think with your head and not over it (as most of us are guilty of the latter).

Once our baseline dyno runs... 

   

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Once our baseline dyno runs were complete, Hank Jr. drove the C5 over to the SLP Installation Center to put it on the lift and allow the exhaust system to cool for removal. Here's a shot of the stock cat-back system, not bad for nine years and 50,000 miles worth of service.

For this particular LS-engine installment we are looking to take a base model 1999 Corvette, which is equipped with a 5.7-liter LS1 engine rated at 345 hp and 350 lbft of torque, and take it to (or exceed) the power level of the 2001 Corvette Z06, which was advertised at 405 hp and 400 lb-ft of torque. This could easily be achieved by employing a nitrous system or even some forced induction, but what's the challenge in that? Let's see if we can turn our tap water into a great tasting energy drink.

For part one of our journey we decided to facilitate better breathing by upgrading the entire exhaust system. While many products are available in the aftermarket, we decided to call upon the pros at SLP (Street Legal Performance) in Toms River, New Jersey. SLP is known as a topnotch leader in LS-powered technology. SLP designs, manufactures, and tests the majority of its products in-house, as quality control is of utmost importance. Whether your needs include something as minor as a gasket, or something as major as an all-out, firebreathing monster, SLP has you covered.

Upon arrival at SLP, Hank Daniecki Jr., director of engineering at SLP, greeted us. Our first order of business was to strap the Corvette on SLP's Super Flow chassis dyno to get some baseline numbers. After a couple of runs our stock 6-speed '99 rolled to the average tune of 312 hp and 323 lb-ft of torque-pretty impressive for a bone-stock LS1. After a little mathematics, that equates to an estimated 360 hp at the flywheel (that's 15 hp more than it was rated at).

We were impressed, both by the quality of SLP's parts and the ease of installation. Better still were the "after" dyno results. Not only were the peak numbers excellent (338 hp/348 torque) but the important digits under the curve were outstanding as well.

We are on our way.

Once all of the oxygen sensors...        read full caption Once all of the oxygen sensors were removed, Hank began removal of the cat-back exhaust assembly-these units are separate from left to right. Beyond removing the flange bolts from the axle pipe, the remainder of the assembly slides out from a rubber hanger mount. In order to complete the removal process, Hank was required to remove the fasteners from the sway bar mountings. Once the sway bar was swung to a lower position, the mufflers were easily removed.

The next order of business...        read full caption The next order of business was to remove the fasteners holding the H-pipe to the exhaust manifolds. Once those are gone, the front and rear fasteners were removed and the H-pipe dropped from beneath the C5.

SLP Technician Hank Daniecki...        read full caption SLP Technician Hank Daniecki Sr. was chosen to perform the installation. The first action Hank Sr. performed was to soak down all fasteners with a penetrating lubricant; this will aid in easy removal. Next, Hank Sr. began by removing all four oxygen sensors (pre- and postcatalytic converter).

Once the C5 was reacquainted...        read full caption Once the C5 was reacquainted with the earth, Hank began removing the battery and engine shields, along with disconnecting the ignition wires, coil pack assembly and exhaust manifold bolts on the passenger side. Be careful, as you are required to carefully remove the oil dipstick tube from the engine.	Shown here is the difference...        read full caption Shown here is the difference between the stock exhaust manifold and the SLP 1 3/4-inch long tube header. A quick visual indicates that we are on our way to better e.t.'s. Once the SLP header is bolted in place it's torqued to 22 lb-ft. It's critical that the instructions be followed carefully. SLP includes a generous amount of heat sleeve that needs to be applied to the wiring harness on the passenger side. Due to tight tolerances, the harness will get hot and melt if this precautionary measure is not taken. The passenger side is now complete.	The driver side header requires...        read full caption The driver side header requires the additional removal of the steering shaft, alternator and the valve cover in order to facilitate easier removal and installation (along with similar items from the passenger side).
Here it is-our completed installation....        read full caption Here it is-our completed installation. All of SLP's components fit like a glove-no cutting or welding was required at anytime. This was a true bolt-on modification that added awesome looks and, we hope, some horsepower.	Once the under-hood items...        read full caption Once the under-hood items were buttoned up, we headed back under the vehicle to install the H-downpipe, high-flow cats, H-pipe/balance tube assembly, and "Powerflo" cat-back exhaust. Hank threads in the oxygen sensors prior to hanging each exhaust component to ease the process.	Hank Jr. also recommended...        read full caption Hank Jr. also recommended that we install SLP's "FlowPac" cold-air package. This kit consisted of a "Blackwing" filter assembly and smooth bellow. If we're helping the C5 exhale, it makes sense to help it inhale at the same time. Naturally, this doesn't apply just to LS1 Corvettes, but any internal combustion engine.
After the install we took...        read full caption After the install we took the C5 over to Raceway Park in Englishtown, New Jersey. After a few runs the C5 blistered the quarter-mile in 12.55-seconds at 112 mph on stock tires. After some research and a look back into the Source Interlink Media archives, we found that a stock C5 of this vintage generally covers the quarter-mile in anywhere from 13.0-13.3 seconds. Victory! We gained about a half of a second of e.t. with rather simple boltons. Stay tuned as we up the ante with a set of cylinder heads, camshaft and intake manifold to aid in the annihilation of our goal. Photo: Thomas Lyman.	Once back on the dyno, the...        read full caption Once back on the dyno, the C5 pumped out 338 hp and 348 lb-ft of torque. That's a gain of 25 hp and 24 lb-ft of torque at the wheels. Not bad for an exhaust swap and a cold air induction. Hank Jr. also leaned out the air-fuel ratio a little as it was running rich (12:1 range). At this point we figure our engine horsepower to be at around 398, and that's only seven shy of our goal.