2004 Chevrolet Avalanche - Pac It In - Tech

The PerformancePac includes a High-Flow Cold-Air Induction System, stainless steel shorty headers, a stainless steel PowerFlo cat-back, 1.85:1 rocker arms, and SLP's dyno-based performance tuning contained in a DiabloSport II programmer. The goal of each kit, according to SLP, is to create a package that significantly improves performance without adversely affecting drivability.

Much of the performance increase we saw came from the simple fact that the new setup allows more air in and out of the Avalanche's LM7 powerplant. SLP's Brian Reese agreed, and took it a step further: "With our package," he told us, "the motor is leaned out at wide-open throttle, improving performance over the rich factory settings."

Of course, an engine must be able to take advantage of increased airflow, and that's where the switch to 1.85:1 rocker arms pays off. "The key ingredient in the package is the high-lift rocker arms," asserts SLP's Reese. A stock LM7 cam running 1.7:1 rockers specs out at 0.457/ 0.466-inch lift and 191/190 duration at 0.050-inch. Bumping up the rocker ratio increases the lift to 0.497/ 0.507-inch, which is certainly a step in the right direction.