 That's Spintech President...  That's Spintech President Ron DiDonato showing off the new the pipes |
 The stock GTO exhaust system...  The stock GTO exhaust system weighs 76 pounds as you see it here... |
 ...282.9 hp at 5,700 rpm and...  ...282.9 hp at 5,700 rpm and 299.1 lb-ft of torque at 4,100 rpm to the rear wheels ... |
 ...(all of our testing was...  ...(all of our testing was conducted with the manual transmission in Third gear and with the traction control switched off). |
Even though it hails from Down Under, many musclecar fanatics from coast to coast have come to recognize the new Goat as a primo corner-carving, power-shifting, rubber-burning supercar.
However, there's one nagging glitch that some diehards can't seem to get their heads around. It's that goofy exhaust system. Even though Pontiac went to great lengths to reconfigure the original Holden Monaro pipes to create a true dual-path system with four catalytic converters (two per bank), two resonators, two mufflers, and two chrome outlets, it's the way they poke out from beneath the driver-side of the car that gives many observers flashbacks to the Smog '70s and the bad old days when single exhaust systems were as good as it got.
We suspect cost control was the primary reason for Pontiac's decision to retain the Monaro's asymmetric layout. Had the pipes been rerouted to each corner of the car, a new fascia would have been needed and, quite possibly, another round of expensive and time-consuming rear-impact crash testing to validate the revised design.
However, thanks to Spintech, there are several exciting remedies to the exhaust situation that are only as far away as the nearest UPS truck. Dan Long, general manager of Arrowhead Performance, offered up his prized '04 Goat (HPP, Tribal News, July '04) to assist in the testing process. It is thought to be the 10th regular production unit to enter the country, and Arrowhead will soon offer a line of body kits and other high-performance parts and accessories for the amazing 21st century GTO. We'll bring you the complete story. For now, let's strap Dan's Goat to the Universal Technical Institute's Dynojet and see what the various Spintech exhaust systems have to offer.
 First impressions can be deceptive....  First impressions can be deceptive. Though the 1 3/4-inch tubing connector between the intermediate pipes may look like a crossover pipe, it is fully blocked. Pontiac's '04 GTO press kit says, "By blocking the crossover pipe, which is now used only for structural purposes, engineers were able to acoustically tune the system to provide an appropriately raspy rumble." |  The stock tubing measures...  The stock tubing measures 2 1/4 inches all the way back to the mufflers. Then it reduces to 2 inches for the tailpipes. Despite the generous sizing, there are numerous pinch points for clearance, like this one where the tube is crunched down to 1 1/4 inches. |  The Spintech side-exit X-pipe...  The Spintech side-exit X-pipe cat-back system (PN SXGTO4V) retails for $619.95 and couples to the stock head pipes and converters for emissions compliance. All tubing is 2 1/2 inches and weight is 40 pounds (73 pounds total as shown). That's 3 pounds less than the factory siamesed system it replaces. This is going to be a popular addition where emissions compliance is a strict requirement. |
 We were pleasantly surprised...  We were pleasantly surprised to discover that the side-exit exhaust outlets didn't cause cabin drone at highway speed and their reduced backpressure allowed the LS1 to make an extra 11.4 hp and 9 lb-ft of torque (294.3 hp and 308.1 lb-ft). Arrowhead Performance offers a rear fascia skirt (not shown) that covers the void left by stock tailpipe removal. |  Getting down to business,...  Getting down to business, we installed this off road, two-cat X-pipe (PN 9P2GTO4, $425.00) and full-length dual exhaust system (PN 2P2GTO4SR, $439.95) and gained 28.5 hp and 33.9 lb-ft of torque posting 311.4 hp and 333.0 lb-ft. Okay, so it isn't emissions legal, but the extra grunt is very noticeable when the throttle pedal is mashed. This setup uses 2 1/2-inch tubing throughout and twin high-flow honeycomb cats and weighs 69 pounds as shown. |  Thanks to careful engineering,...  Thanks to careful engineering, the installation process is a simple bolt-on affair. Here, Spintech prototype fabrication man Heriberto Ramirez bolts the X-pipe support flange to the stock GTO hanger. |
 Leak-proof ball and cone flange...  Leak-proof ball and cone flange connections secure the X-pipe to the intermediate pipes. |  Dual Spintech Pro Street series...  Dual Spintech Pro Street series mufflers measure a compact 12x6x4 inches, so ground clearance is not compromised. |  Designed to eliminate drilling...  Designed to eliminate drilling and welding, the system's passenger-side tailpipe is supported by this stamped steel bracket that makes use of an existing hole in the frame. |
 After the bracket is slipped...  After the bracket is slipped into position, a steel and rubber hanger is bolted in to accept the passenger-side tailpipe. All of this is included in the full-length exhaust system kit. |  On the driver-side, Spintech...  On the driver-side, Spintech again makes use of existing drilled holes (one of three that secure the stock exhaust heat shield to the frame) that allow the reuse of the stock tailpipe bracket and hanger (albeit repositioned slightly). |  Here's the dual exhaust system...  Here's the dual exhaust system the GTO should have had from the start. The 3-inch tips are made of T304 stainless and will also be available with traditional Trans Am / GTO twin outlet "exhaust splitters" for an additional $80 by the time you read this. |
 Here's the off-road X-pipe...  Here's the off-road X-pipe we tested above (again, it's PN 9P2GTO4, $425), but now, instead of full-length tailpipes, it's connected to a pair of side-exit mufflers (PN SX0GTO4D, $569.95). This complete system weighs 68 pounds as shown. |  The chassis dyno showed the...  The chassis dyno showed the 180-degree-flow, split-case Sportsman mufflers to be a little bit more restrictive than the Pro Street mufflers and linear-flow full-duals, but the numbers still exceeded anything generated by the stock head pipe and cats by 8.9 hp producing 303.2 hp and 316.4 lb-ft of torque. |  It's NASCAR meets Main Street....  It's NASCAR meets Main Street. The twin outlet "extractor"-style tips give the Goat a menacing "come and get it, bee-yatch" vibe and the most aggressive exhaust note of the test. However, from the inside we were surprised to discover that the cabin volume was actually reduced over the full-length pipes and normal conversation is possible any time except during moderate-to-hard acceleration. The rocker panel extensions are missing in this shot because Arrowhead pulled 'em to use as masters for slick replacements we'll show you in an upcoming article. |
Spintech Surprise
 Spintech mufflers get their...  Spintech mufflers get their name from the unique scroll-shaped sound traps welded into the muffler case. They mute objectionable sound waves without inducing unnecessary backpressure. |  Spintech X-pipes use patented...  Spintech X-pipes use patented Dr. Gas welded junctions that allow the exhaust flow from each bank to merge. All Spintech products are made from aluminized 0.065 wall steel tubing, though T304 stainless is optional at extra cost. |  Stock GTO Exhaust: 282.9...  Stock GTO Exhaust:
282.9 hp / 299.1 lb-ft torque |
 Spintech Side-Exit X-Pipe...  Spintech Side-Exit X-Pipe Cat-Back Dual Exhaust:
294.3 hp / 308.1 lb-ft torque |  Spintech Off-Road X-Pipe And...  Spintech Off-Road X-Pipe And Full-Length Dual Exhaust:
311.4 hp / 333.0 lb-ft torque |  Spintech Off-Road X-Pipe and...  Spintech Off-Road X-Pipe and Side-Exit, Cat-Back Dual Exhaust:
303.2 hp / 316.4 lb-ft torque |