With a desire for his car to develop additional horsepower, even when the NOS system was not being engaged, the engine's breathing capacity on both the inlet and outlet sides of the cylinder heads were upgraded with a K & N Filtercharger air filtration system. The inlet tube diameter is larger, while the high-flow cotton gauze element resides in its own partitioned fresh-air box, which is supplied with the kit. The upgraded exhaust system consists of a Borla T-304 aircraft-grade stainless steel Cat-BackTM system, and an intricate set of T-304 stainless steel headers. The headers carry a California Exemption Order number and complement the high-performance exhaust system. Besides adding to the looks and performance of the LT1-powered car, the sound is vastly improved over theOE system, which "chuffed" through a drain hole in a muffler during operation.
In order to accomplish the acceleration desired for the Caprice, the factory rearend ratio was replaced with a 3.73:1 ring-and-pinion. A Hypertech Power Programmer III engine management and shift programmer was installed, which includes program functions to compensate for the speedometer error. The Power Programmer III further improves the vehicle's performance, and was purchased along with a 160-degree "PowerStat." With a simple manipulation of the factory GM software accomplished by following Hypertech's instructions, the speedometer was corrected for changes in both the tire diameter and gear ratio. During the process, the shift pressures were modified for a firmer shift, while the shift points were also calibrated along with the rev limit in each gear. The Power Programmer III allowed us to experiment with shift and rpm calibration at the race track. Changes to the program were made in between runs, taking roughly 10 minutes each time.
Finally, after nearly a year of assembling the project, the Caprice was taken back to Holtville for its final performance evaluation. As shown in the testing chart, the performance for the big car excelled in virtually every test, whether accelerating, stopping, turning in a circle, or blasting around a race track. We are certain that the acceleration numbers would have been even quicker if we had less air pressure in the tires, or installed a set of street slicks. The air pressures were set deliberately high in order to conform to the previous testing parameters that were designed to prevent the tire walls from rolling onto their sides. The most notable characteristics, which were not shown in the test figures, included a major improvement in straight-line stability along with far less chassis roll in the corners. Originally, the heavy car would keel over to one side, then remain relatively neutral during a long corner. The combination of the suspension tweaks and big Pirellis made the car more prone to a slight oversteer condition that was corrected with small inputs in the steering. The lower profile tires combined with oversteer made the car feel more nervous, but boy was it faster! As in more than three seconds a lap faster without using nitrous. In fact, the times were faster than some of the lightweight racing sedans that compete in the Improved Touring classes of SCCA. Lights, siren, bullhorn...action!
There was one casualty during the test, its demise most likely hastened by our rapid steering inputs. The factory power steering pump rolled over and played dead on the last lap of the road course. Typically, the car was tested in three-lap dashes, then allowed to cool down. The driver neglected to properly count the laps during the last segment and ran an additional lap. At almost the same moment that the power steering pump failed, the stock DOT 3 brake fluid boiled, caused by shear overheating and overuse. This was not caused by the upgraded brake components, however, because they survived the three-lap dash far better than the previous "agricultural racer." If anything, the sticky Pirelli P-Zero tires saved our tail this time by allowing the thundering monster to make the harrowing turn with very little braking and steering. With the skid pad being the last test on the agenda, it proved a more laborious task to keep the car in a crisp circle, potentially hurting our final numbers. The inability to balance the car on the limit with a rapid steering input may have cost us a few tenths of a second during the timed circles.
Ultimately, we left the test satisfied that we reached our goal of improving the big car's performance throughout its entire range. This would hold true, whether making a trip to the drag strip, running the big sled through the twisties, or making a panic stop. The ride is more firm, but enjoyable, while the sound of the car has improved immensely. All of these upgrades were accomplished for less than the cost of a used Impala. Of course, any Impala owner would be glad to have these additions to his or her machine.