When performed correctly on any car that needs them, exhaust upgrades accomplish three things: Your car will be quicker, have an authoritative tone, and run more efficiently. With those benefits in mind, we decided to bolt a set of American Racing Headers' 1.875-inch headers and free-flowing cats onto an '05 GTO. The Goat in question was previously fitted with an after-cat system from Corsa. Since the new components are the next logical step toward power production, we proceeded with them.
Manufactured in 304 stainless steel, American Racing's headers are strong, look great, and shouldn't corrode if properly cared for. They also feature a merge collector with a scavenger spike. "Merge collectors are a staple of our headers here at American Racing Headers," says Nick Filippides, the company's project manager. "We found the merge allows us to maintain strong low-end torque, without having to sacrifice top-end horsepower. We use the scavenger spikes to direct the exhaust through the 3-inch collector."
Though this technology isn't uncommon on many of today's high-end header systems, it usually comes at an additional cost. American Racing's headers, however, are sold with this NASCAR-derived feature as standard equipment.
According to the company, the gains we saw could have been higher if we had opted for the smaller 1.75-inch primary headers, as they would've been more appropriate for such a tame GTO. We went for the larger tubes because planned future mods will require them to produce the most power.
The first step was to establish...
The first step was to establish a baseline. Our '05 GTO benefits from a Corsa Sport after-cat but is otherwise stock down to the paper air filter. Attached to the Dynojet rollers, the GTO put down 325 rwhp and 325 lb-ft of torque. These figures were supported by another backup run.
The components were installed at AntiVenom LSX Performance and Repair in Seffner, Florida. This company specializes in late-model GM performance buildups on Corvettes, F-bodies, and GTOs. Let's follow along as owner Greg Lovell and William Edgar remove the restrictive stock exhaust and install the shiny, free-flowing parts from American Racing Headers.
Conclusion
The installation of the header system was good for a solid 19 rwhp and 24 lb-ft of torque. Afterwards, AntiVenom's Greg Lovell altered the tune a bit and picked up an additional 6 rwhp. After all was said and done, our GTO gained 25 rwhp and 21 lb-ft of torque.
Throughout the powerband, there was a consistent gain. Down low through the midrange, torque picked up substantially. This can be felt on the street as we now have a tough time keeping traction. When it does hook, the power and sound are brilliant.
For anyone who has ever installed a long-tube header system on a late-model car, the installation was straightforward. The results are worth the effort.
 This is what we're working...  This is what we're working with: a set of American Racing Headers' 1.875-inch long-tube headers with high-flow cats (PN GTO0678WC; $1,337.70 retail). They're also available in 1.75-inch primaries, without cats, or with an x-type pipe. The company will also make custom systems. Oxygen-sensor extension wires, gaskets, and clamps are included in the box to make the install smooth. |  One of the coolest features...  One of the coolest features on the American Racing header is the merge collector with scavenger spike. These increase the collector's efficiency and, according to Nick, translate into additional low and midrange power. |  After the engine had a chance...  After the engine had a chance to cool down, the battery was disconnected and the fuel rail covers were removed, along with the air intake system, to gain access to the exhaust manifolds. Also, the factory strut-tower brace, secured by 13mm bolts, was taken out along with the radiator shroud. |
 This is the factory exhaust....  This is the factory exhaust. While the 2.5-inch-diameter pipe supports a lot of power, the horsepower-robbing catalytic converters won't. They'll be replaced with high-flow metallic substrate cats. Regardless of the presence of catalytic converters, long-tube headers aren't emissions legal. Cats can be used to reduce noise levels. |  All of the oxygen sensors...  All of the oxygen sensors will be used again, so they will be carefully removed. We found out that '04-'06 GTOs use a different oxygen sensor for each year, so finding a replacement can be involved. |  AntiVenom started on the midpipes...  AntiVenom started on the midpipes at the after-cat flange. The 15mm bolts were easily removed, and our Corsa system supplied us with a hex-head on the opposite side of the bolt. |
 The flange just after the...  The flange just after the manifolds on each side is a ball-joint style connection. They're held together with 15mm bolts as well. |  Once the flange bolts were...  Once the flange bolts were removed, the midpipes dropped down easily. |  Once the manifolds were removed...  Once the manifolds were removed by way of the bottom of the GTO, the gaskets were set aside for reinstallation, and the manifold was compared side-by-side to the header. It's clear the American Racing headers are more efficient in scavenging the exhaust gases-a sharp contrast to the more restrictive iron manifolds. |
 AntiVenom's Greg Lovell and...  AntiVenom's Greg Lovell and William Edgar moved up to the exhaust manifolds. To prevent cracking a spark plug-a common mistake during a header install-they used a 5/8-inch spark-plug socket to get them out of the way before directing their attention to the 10mm manifold bolts. |  These body braces were removed...  These body braces were removed on both sides to make some room before the new headers were lifted in. |  Since both headers will be...  Since both headers will be slid into place from the bottom, it was necessary to drop the steering rack to gain enough clearance. This requires draining the fluid and disconnecting the steering column linkage. The passenger header was installed and secured using the factory gaskets and supplied bolts. |
 The midpipe with the cat was...  The midpipe with the cat was slipped onto the header collector and loosely bolted to the flange on the after-cat. The clamps provided with the headers are the same ones used on the factory Corvette exhaust and provide a tight, leak-free connection. |  The tricky part was the driver-side...  The tricky part was the driver-side installation because the steering column linkage runs through the header's primary tubes. It needed to be disconnected. Since we opted for the 1.875-inch primaries, we saw why we had to lower the steering rack. The large-diameter pipe is a tight squeeze on the way up. Having the rack out of the way frees up a few crucial inches, allowing the pipe to slide into place. |  With the steering components...  With the steering components out of the way, the stainless header was pushed up into position on the driver side. |
 Back up top, the factory exhaust-manifold...  Back up top, the factory exhaust-manifold gaskets were reused, as had been the case on the passenger side. Though American Racing supplies new gaskets in the kit, the factory gaskets are reusable and seal up tightly. |  Here you can see how the driver-side...  Here you can see how the driver-side header wraps around the steering column linkage. Once the reservoir was reconnected, it was filled with automatic transmission fluid. To flush the bubbles out of the system properly, the front tires were raised off the ground, and the steering wheel was turned lock-to-lock 12 times without starting the engine. Once done, the engine was started, the system was examined for leaks, and the fluid level was checked. |  The four 15mm bolts that connect...  The four 15mm bolts that connect the midpipes and the after-cat system were tightened, while the header clamps were left loose. Tightening these bolts will align the midpipes, so it's a good idea to start with these. |
 The final step is to tighten...  The final step is to tighten the provided exhaust header clamps' 15mm bolts. |  The new American Racing Headers'...  The new American Racing Headers' system looks great and fits perfectly without reducing ground clearance. |  We put the Goat back on the...  We put the Goat back on the Dynojet's rollers for another round of pulls. To our surprise, we gained 19 rwhp and 24 lb-ft of torque without any tuning. Greg made some minor adjustments to the tune and was able to free up six additional ponies, but torque fell off a bit when timing was added. Thanks to the poor intake system on the late-model GTOs, inlet air temperatures soared. We read more than 110 degrees on every pull. This greatly limited how much timing could be added. Run 1 was our baseline, Run 4 was after the headers, and Run 13 was after the tune. To ensure accuracy, each pull was supported by additional runs. |