Class Pulley
With our mechanical mods completed, it was time to unstrap our GTO off of the SuperFlow dyno and put it on the lift over at SLP's installation shop, where technician John Forner helped perform the installation of our next piece of high-performance equipment, which was an SLP underdrive pulley. SLP's unit is a machined piece of steel beauty that is precisely manufactured to exacting tolerances. Precision is important for an underdrive pulley, and installation must be performed with a new bolt whenever the damper/pulley is removed from an LS engine. If you don't do it, that pulley will come right off and make a nice run for the border, right under your car and to the curb. Thankfully, SLP's part number 100226 ($249) is a proven piece in many race applications. On our GTO, it took about two hours of time to install. After it was torqued into place, we headed back over to the SuperFlow dyno and watched the rollers spit out peak figures of 365.2 rwhp at 6,000 and 349.9 at 4,800 rpm, for a gain of 7.7 hp and 2.7 lb-ft at the wheels. This goes to prove that, time and time again, underdrive pulleys and LS engines are indeed best friends.
Chapter 2: TT Performance
With our GTO fresh off the SuperFlow dyno and equipped with all our latest bolt-on goodies, it was time to mosey on over to TT Performance where proprietor Matt Sorian was able to take us in for our next round of modifications: the exhaust system. Obviously everything upstream was now opened up, so it only made sense to free up the backside of things. We had heard of some people getting incredible gains from cat-back exhausts and headers while other enthusiasts found no gains at all, so we decided to find out for ourselves what the real deal was.
Now obviously, going from one type of dyno to the next is not the best way to perform back-to-back testing, but in this day and age, many of us enthusiasts have come across both the eddy-current type and the inertia dyno at least twice in our lives. As the market for chassis dynos continues to grow, we see more and more shops using different types for their particular customers. Some prefer a load-bearing dyno as it can help tuners work with turbocharged cars, while others prefer the simplicity and repeatability of the inertia dyno. Either way, you can't go wrong, but it's always good to test your car unchanged between two shops. Knowing that SLP uses an eddy-current SuperFlow dyno and that TTP uses a DynoJet 248c inertia dyno we made a baseline run to reestablish ourselves at TTP in Passaic, New Jersey, with no changes made to the car. The runs were made within a few days of each other, so the car was still on the same tank of gas and the weather was similar.
With the Head Poncho strapped on the rollers at TTP, we baselined ourselves with 338.2 hp and 324.1 lb-ft at the wheels. This is down compared to the numbers that we picked up at SLP, but now we knew where we stood between the two dynos. So, our first mod was the replacement of the cat-back exhaust. Looking at all the various exhaust companies that offer a system for the GTO can be dizzying. Most are of high-quality construction, but we went with the 3-inch cat-back offered by Stainless Works. The advantage with using the cat-back from Stainless Works is that it is a fully adjustable system that can help you get a better fit under your car. Because no two cars are alike, the slip-fit design of the Stainless Works system (part number 05GTOTMCB, $867) allows you to clear items that you normally couldn't with a fully welded system. In addition, the X-pipe crossover system and turbo-style mufflers offer less noise and interior resonance compared to some other systems on the market.
 The fit was top-notch with...  The fit was top-notch with the Stainless Works system and the looks were truly a sight to behold. Ground clearance was also not an issue. Power gains were 3.0 rwhp and 1.2 lb-ft of torque on the DynoJet. We attribute this fact mostly to the factory exhaust system's already good design. Dig the GTO lettering we put into the rear panel. |  Next up for testing was a...  Next up for testing was a set of long-tube headers by Stainless Works. The 1.75-inch primaries are a perfect match for our LS2 and the all-stainless construction will give us years of good looks and great performance. |  The header flanges are fully...  The header flanges are fully TIG-welded from the inside for a leak-free fit. The laser-cut flanges are also pretty thick, which makes sealing top notch. |
 Since our header system was...  Since our header system was ordered with catalytic converters, we're happy to see a set of Random Technologies converters as part of our system. Random makes the best cats out there and we like how Stainless Works has chosen them for its systems. |  To facilitate the installation,...  To facilitate the installation, we needed full access to a lift. Thankfully, TTP was happy to oblige. Because the headers do not come with gaskets or bolts, we utilized TTP's header installation kit to complete the install. Once the last bolt was tightened down, the Stainless Works long-tube headers fit with plenty of clearance around the floorpans and steering system. |  Before we made our first run,...  Before we made our first run, Matt Sorian of TTP gave the car a quick tune. Based on his experience, long-tube headers can sometimes lean a GTO out too much because of the additional engine airflow. So with a little fuel added, we were impressed with our complete exhaust system gains of 11.9 rwhp and 12.6 lb-ft of torque at the wheels. |
Back at the track, our new best e.t. is a 12.286 at 110.8 mph. Compared to where we were prior to our bolt-ons, that's over a three tenths reduction in e.t. and a full mph over our previous best of 12.620 at 109.6. Make way for the Head Poncho!