There has been a lot of talk regarding the GNX suspension sold by Kirban Performance Products. From what we have seen, a love-it-or-hate-it attitude exists regarding this system. The hard-core racers scoff at the idea of spending so much money (A complete kit with an exhaust system is $2545.) for a reproduction suspension piece when a race rear swaybar or adjustable control arms would provide similar traction enhancements for less cash. The collectors are crazy about the idea of the GNX-like exclusivity and improved street performance from the ladder bar/torque arm setup. We at GMHTP like to ride the fence. We're always looking for a few extra tenths here and there, but our cars are our daily (and sometimes our only) transportation, so reliability and OEM-style engineering takes precedence over ET reduction. We hear pretty much what you hear, that this system is supposedly the real deal, so you can see why we've had our eyes on it ever since its introduction in 2000. After a few conversations with KPP owner Dennis Kirban, we learned that the gentleman who undertook this project (a fellow GN and GNX owner) spared no expense in accurately recreating the suspension responsible for the GNX's blistering 0-60 and quarter-mile times back in 1987. For people who try to put as many street miles on their cars as possible, we couldn't see a downside to this system--provided it lived up to its billing. Once we ordered it, we put in a call to Cotton's Performance Center regarding the installation. Jack Cotton is well-versed in turbo Buick restoration and performance, and has fabricated every square inch of his 9-second T-Type himself, so we knew we'd be in good hands.
Our test mule was a daily-driven 152,000-mile Turbo-T. This old warhorse was basically stock until the fuel system took a dump at 100,000 miles. Now it sports a few minor modifications, such as green stripe injectors, an adjustable fuel pressure regulator, a Bosch inline fuel pump, a high-flow air filter, and a 3-inch downpipe/dump tube that we snagged for $100 off the Internet. With nothing more than a Red Armstrong 108 race chip, good gas and a cooled intake, it spun its way to a 12.94 ET on ET Streets and a Vericom-recorded 4.99-second 0-60 time on real radials at Englishtown, New Jersey's Raceway Park. Traction aids were ripped (read: uninflated) airbags, SouthSide Machine lift bars, a pinion snubber, and a flaring, downtrodden stock transmission.
Our goals are simple: We're going to run this system over the coals and see how well it holds up. Launch it hard on slicks and street radials and compare the timeslips. Hang the tail out in fast corners and wait for it to break loose. Report any change to the car's ride characteristics, good or bad. And listen for the sounds that ill-fitting suspension parts and exhaust systems make. But first let's tackle the install, quoted by Kirban Performance Products to take four to five hours under normal conditions.
|Drag strip Results|
|1987 Buick Turbo-T, stock rear suspension|
|60-foot time||elapsed time||mph|
|1987 Buick Turbo-T, GNX rear suspension|
At The Track Although just a couple of months separated our baseline test from this one, the weather was completely different. Our 12.94 was turned in 94Â° heat and high humidity in late July, and it was in the mid-60s when we rolled into Raceway Park for the second time. We needed a way to compare apples-to-apples, so we started by preparing our 152,000-mile Turbo-T exactly the same way both times. Once parked, the Schrader valve was removed from the fuel rail and we pumped out the 93 octane. When the tank was nearly dry, we filled it with five gallons of super-high octane racing fuel with a minimum motor octane of 112, and our BFG radials were swapped for ET Streets set at 15 lbs. Red's 108 race chip went in, and our dump pipe was opened up. A shakedown run was made to verify 23 pounds of boost, a reasonable amount of knock retard below 7Â° and O2 millivolts above 750. Once these parameters were established, we stuck bags of ice onto the inlet pipe and doghouse and let it cool down. Forty minutes later, I approached the line with the coolant temp around 135Â°, and after a decent burnout, staged with the coolant right at 160Â°. Once the pre-stage bulb was lit, the boost was brought up, and although the new torque arm setup would hold in excess of 7 lbs. on the line, the T's crappy brakes couldn't keep the car from creeping ahead. We decided to launch at zero boost, which would duplicate the amount we could hold before the GNX system went on. When the lights came down, the slicks hooked like glue, and instead of loading up the right rear, the car left perfectly straight. We saw a 1.84 60-foot come up on the scoreboard as the boost hit 23 lbs., and it held steady all the way through the lights. The timeslip read 12.85 at 102, so we decided to bump up the fuel pressure to recapture our missing mph. The next few runs were made without any launch boost, and with the higher fuel pressure we were able to record a 12.81, 12.77 and 12.79 with trap speeds in the mid-105s. Since the conditions were much more favorable on this day, we were able to deduce that the cooler air was responsible for almost two-tenths reduction in ET. Now we can race.
After another 45 minutes, I rolled to the line. I slowly brought the rpm up, and the VDO boost gauge hit 4 as I crept into the staging beam. The Turbo-T lunged to a 1.83 60-foot time. Wheelspin was nonexistent, and although the stock trans hesitated briefly between shifts, both were made smoothly. The car felt really strong as it sailed through the traps, and my gut told me we had a winner. After taking the last turnoff before the sand trap, I flipped the heater and the fan on and headed back. Once in front of the clock, I was pleasantly surprised at the 12.47 at 106 and change. An hour and nine minutes later, we backed it up with a 12.48. Taking into account the 12.77 recorded in the very same air with no launch boost, we gained a solid three-tenths!
Satisfied that the GNX suspension did the trick on slicks, we swapped our street radials (BFG 265/50R15) back on. In July, our Vericom had witnessed several 0-60 runs in the 5.3-second range, and we managed to crack 4.99 on our last attempt, a much less exciting run than those previous. Since Mr. Armstrong builds 27° of timing into his 108 chip through First and Second gears, getting into the turbo on street tires was a dicey proposition. With the panhard/torque arm suspension keeping our T's suicidal tendencies in check, we knew our times would drop--the only question was, by how much?
A quick burnout cleaned off the radials, and an overzealous launch decimated the tires with a 5.2-second result. I quickly returned to the starting line and hot-lapped the car, begging my now-boiling brake fluid for one more pass. When I saw four pounds, I released the brake and let the car accelerate out before flooring the gas. The tires were still spinning, but once they hooked up the Vericom's beep ended the run before we knew it. The result? 4.59 seconds to 60--a four-tenths improvement.
The revised rear geometry provides an entirely new sensation while accelerating away. Previous banzai blasts easily twisted the live rear, lifting one side and jamming the other into the pavement. The GNX suspension lifts the rear evenly, pushes the nose down, and turns all of that torque into forward motion in a hurry. Both wheels grab equally, and the car goes absolutely straight. And after two months of commuting on the disasters that are New Jersey roads, I was impressed with the solidity of the GNX system. The crossmember that attaches the ladder bar provides added chassis strength, and when combined with the T's other braces, completely rids the car of the squeaks and rattles associated with a 14-year-old performance car. The panhard suspension provides a more solid suspension feel than the factory 4-link, and it's performed flawlessly. And besides a slight persuasion of the crowbar kind made to the exhaust system (thanks to our derelict downpipe), the fit is excellent and the sound is perfect. If there's a more comprehensive suspension upgrade for a turbo Buick, we've yet to see it!