Pursuing Performance

We wanted to make sure the Caprice's lubricants and filters were up to snuff prior to hitting the dyno, to ensure that we weren't introducing other variables into the equation. Besides, the dyno can give a car a real workout, so having fresh fluids is always a good idea. To begin, we used standard Valvoline 5W30 (factory spec) along with a K&N oil filter. The fuel filter was also replaced with a Fram service replacement part.

The ignition parts on our Chevy were also well worn, so we swapped in a fresh set of stock-spec AC plugs and a set of MSD plug wires. The wires for the LT1 are somewhat unusual since all Gen II small-blocks use the Opti-Spark ignition system, which is based in a distributor mounted behind the water pump. The task of changing these wires looks deceptively simple, but is actually a major chore, since the wires are routed behind the front accessory drive components and behind the exhaust manifolds in steel looms. It's worth doing on high-mileage cars, though, since this routing allows the engine's heat to take its toll on the LT1's ignition wires.

This being the first trip to the rollers for the Caprice, we wanted to establish a solid baseline. The first pulls were made as the car came off the street--210-degree coolant, 91-octane fuel, and with all factory air intake and exhaust pieces in place. The Caprice has an excellent cooling system, but the factory programmed the electric fans to stay off until the coolant reaches nearly 225 degrees to keep idle emissions clean. This is reflected in the temp gauge as the needle reaches just shy of the three-quarters mark. When the needle sweeps past the straight-up point (typical for non-highway driving), performance falls off substantially judging by seat-of-the-pants input. Our first pulls were made at around 210 degrees, and showed 217 hp and 276 lb-ft.

There are several means of activating the cooling fans at lower temps, including computer reflashing and aftermarket programmer devices. Both are effective, but we decided to take a more mechanical approach by using one of Jet Performance's fan controller switches. The switch comes with wiring to tap into the factory harness and triggers the fans at a lower temp, which in turn allows the engine to run closer to the temp dictated by the thermostat, in this case around 195 degrees. This simple change bumped power up to 222 while torque climbed to 280 lb-ft.

Lowering the fan switching temp may cause the fans to turn on frequently, as the coolant will still be fairly warm thanks to the stock thermostat. The Gen II small-blocks use a uniquely designed thermostat, and while replacements are readily available, all the ones we found at the local parts store were for the stock temperature. Fortunately, the aftermarket offers cooler T-stats for the LT1, so we sourced one from Jet and tried again. Lowering the coolant temp further should continue to boost power, and the next round of pulls confirmed this as we gained an additional 2 hp. We suspect that this change may normally be worth a little more, as our coolant was already fairly warm from previous tests.

Another area often compromised on late-model vehicles is the air cleaner and its ducting. Since auto manufacturers have to subject their vehicles to drive-by noise tests, most air cleaners are baffled to reduce intake "roar"--the sound your mom's station wagon used to make when you flipped the air cleaner lid over. The LT1 Caprice seemed strangled judging by the look of its stock air intake setup. The filter box itself is fed by a small, oval inlet that faces the back of the headlamps and the duct to the mass-airflow sensor (MAF) has a huge resonance chamber with offset inlet and outlet connections. Another resonance chamber is mounted atop the intake manifold, though it doesn't seem to obstruct airflow. We figured a more direct shot to the throttle body would have to help output at least a little.