We all like to go faster, but the path to lower e.t.'s isn't always through engine upgrades. There's performance to be found in the remainder of the drivetrain as well. Adding a higher-rpm stall torque converter to the 4L60-E or 4L65-E automatic transmission behind your GTO's LS1 or LS2 powerplant will improve acceleration, providing that the stall speed is properly matched to the engine output and torque characteristics. Another advantage is the stealth nature of a converter upgrade. No one will know about it except for you. In fact, it will be very difficult to detect-even by the dealer-which is a major plus if your GTO is still under warranty. This can't be said for more obvious underhood mods.
The torque converter, which is a hydrodynamic fluid coupling device, links the engine and transmission and acts as a torque multiplier during the stall and acceleration phases. Providing your GTO with the optimum stall speed will result in the best performance.
As the fluid is pumped through the converter, there are energy losses, however, leading to a coupling efficiency that in the past could never achieve 100 percent. With the advent of the lock-up torque converter, the industry was forever changed. Lock-up converters by nature add a clutch that physically links the pump and turbine, effectively changing the converter into a purely mechanical coupling upon lock-up.
This is a benefit to those installing a higher-stall speed converter when using the overdrive transmission because at highway speed with overdrive, cruise rpm will be lower than stall rpm. There would normally be slippage, which increases heat and reduces reliability, however, the lock-up feature has eliminated the slippage so now you can run a higher-stall speed converter to improve torque multiplication (performance) off the line and still cruise in overdrive at low rpm without worry.
Choosing a converter upgrade is generally determined by matching the converter stall speed to the engine's powerband, vehicle weight and rear gear, among other factors. According to Terry Hendrick, of Precision Industries, "Stall speed is determined by the engine's peak torque and is the rpm at which the converter will hold the engine speed and not allow further increase. Since many times when you rev the engine against the brakes the torque will overcome braking power and the car will start to push through them before stall speed is reached, hobbyists commonly use flash speed to discuss converters; that is the engine rpm at which the car begins to move forward when the gas pedal is depressed on launch.
"The real trick is to produce a torque converter that's strong enough to handle increased stall speed and still lock up efficiently. For owners of late-model F-bodies and GTOs, the factory torque converters stall between 1,500-1,800 rpm, depending on power. In general, for the majority of street applications, our Vigilante series of lock-up converters with a stall speed of between 2,800-3,200 are recommended."
Precision Industries developed the Vigilante line of converters from a clean sheet of paper and they contain state-of-the-art features including a specially designed and heat-treated 4130 alloy machined impeller hub, along with a heat-treated 4142 alloy turbine hub.
Precision Industries was the first aftermarket torque converter manufacturer to design, develop and manufacture multi-disc torque converters. In addition to carrying an industry-leading written unconditional two-year warranty, each converter is eligible for one free stall adjustment within two years of the date of purchase.
Follow along as we go though the removal of the factory unit and install a Vigilante torque converter into an '06 GTO owned by Bob Cook of Allen, Texas. In addition, a quality transmission cooler from Hayden and Amsoil's synthetic ATF will be added to ensure that the fluid in the transmission remains cool under the most demanding conditions. Labor will be put into the capable hands of Real Performance Motorsports (RPM) of Lewisville, Texas, and technician Manuel Bejar. Once installation is complete, it's off to the dragstrip to find out if the Vigilante converter can live up to its reputation as one of the best bang-for-your-buck performance modifications for late-model GM vehicles.
Drag Testing
Drag testing was conducted before and after the installation of the Vigilante torque converter on back-to-back weekends. Baseline testing of the stock torque converter was conducted at the Texas Motorplex in Ennis, Texas, a quarter-mile racing facility. Testing of the Vigilante torque converter had to be conducted at North Star Dragway in Denton, Texas, an eighth-mile racing venue.
Although both tracks are located within 60 miles of each other, NHRA conversion factors were applied in order to compensate for differences in elevation, temperature, humidity and barometric pressure. The conversion factor for Ennis was 0.9744, while North Star Dragway calculated out to 0.9835.
Facility:Texas MotorplexNorth Star DragwayElevation:500-ft640-ftTemperature:78.8-deg72-degHumidity:54 percent46 percentBarometric Pressure:29.85-hg30.21-hgCalculated D/A:2,201-ft1,461-ftConversion Factor:0.9744 e.t.0.9835 e.t. Configuration–Best60-ft 330-ft1/8 ET1/8 MPHStock Converter2.005.568.4585.64 Vigilante Converter1.865.318.2184.99Delta0.140.250.24<0.35> Converted–Best1/8 ETStock Converter 8.23Vigilante Converter8.07Delta0.16 Configuration–Average60-ft 330-ft1/8 ET1/8 MPHStock Converter2.025.588.48 85.34Vigilante Converter1.885.358.2684.44Delta0.140.230.22<0.{{{90}}}> Converted–Average1/8 ETStock Converter 8.26Vigilante Converter8.12Delta0.24Tools And Supplies
Conclusion
After installing a 3,200-rpm stall Vigilante torque converter, this '06 GTO took yet another leap forward from a performance standpoint. According to Bob Cook, "The car gained almost two-and-a-half-tenths in the eighth-mile and averaged over two-tenths even when the engine was heat soaked. The converted bests are a bit misleading since the baseline established at Ennis was done as part of the Texas Muscle Car Challenge Series and there was ample time for the engine and transmission to cool down before each pass. Nonetheless, with a prior best of 13.08 in the quarter-mile (uncorrected), the Goat should now easily achieve consistent 12.80s in the quarter. After reviewing the results, the 60-ft. times were significantly improved with a tenth-and-a-half increase.
"As expected, once a performance torque converter was installed, the Mickey Thompson ET Street radials (HPP, Oct. '07, "Hookin' up a Goat (and a Bird) on a Budget") responded and hooked without any evidence of wheel spin. From a normal driving perspective, you really can't tell that there is a high-performance converter installed. Part-throttle acceleration and overdrive lock-up on the highway have been unaffected. Any additional heat that the higher-stall converter may generate has been more than compensated for with the addition of the transmission cooler and AMSOIL synthetic ATF."
The Vigilante converter operates much like an OE unit until the throttle is mashed and it flashes higher, instantly propelling the LS2 engine into the power band. Although the Vigilante torque converter is not the cheapest performance modification out there, it's a very good bang-for-your-buck. If you're in the market to take your automatic-equipped late-model GTO or Firebird to the next level, consider giving Precision Industries a call and let them custom-build a converter for you in a flash!
