Safe and sane modifications to the 5.3L LM7 produce 480 RWHP
The strategy throughout was to encourage low-end torque, up power output, and maintain a semblance of fuel mileage from the most common LS-series engine, the LM7 5.3L V8 found in the light-duty Silverado truck, GMC and Chevrolet SUV’s since the ’99 model year. In stock form, this (’03 model) 325ci aluminum head/iron block engine produces 285hp at 5,300 rpm and 325 lb-ft at 4,000 rpm. With a flat-top piston, the 61.5cc combustion chambers yield a static compression ratio of 9.5:1. Intake- and exhaust-port volume is 210 and 75cc, respectively, and the valves are 1.89 and 1.55 inches. Though we did this to an existing engine, 5.3L V8s are all over recycling yards these days and at a less of a premium than the 5.7L Camaro/Corvette engine. All you lose are 31 cubic inches—and an aluminum cylinder case.
When the rest of the world finally shucks the venerable small-block, it will find an amazingly simple and highly-engineered work of art ready to thump in stock form. From the bottom end up, you’d swear you were looking at a sophisticated import V8, more recently of the Japanese or German variety. We know unequivocally that in completely stock form even the cast-part, lower echelon LS engine will absorb tremendous abuse (skillions of 700hp pulls on nitrous oxide) without failure. If it can withstand heinous, heaped-on terror as a dynamometer mutt, it’s quite likely to live the life of Methuselah on the open road.
Armed with this knowledge, we worked with Vinci Hi-Performance (VHP) to encompass the usual bolt-on suspects and then advance to more involved systems, all done without opening up the short-block assembly. In effect, it’s all bolt-on, but all of it doesn’t necessarily bolt right on. The brands we used were favorites of VHP’s, stuff they recommend or incorporate on a regular basis.
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| 1. Crane Cam Quick-Lift kit and dual valve springs |
VHP’s modus began with a Crane Cam Quick-Lift kit that converts the OE assembly from a “net lash” configuration to the installation of adjustable billet stud-mounted 1.8:1 rocker arms (1.7:1 stock). The parts include stout chromemoly 5/16-inch diameter (0.080-inch wall) pushrods, locks and adjusters, studs, and guide plates. In anticipation of a lumpier camshaft, we included Crane dual-coil valve springs rated at 110 pounds on the seat and 350 pounds open. On VHP’s rollers, stove-stock LM7 recorded 236.7 hp at 5,200 and 289.2 lb-ft at 4,000rpm. After the Quick-Lift swap, the motor netted an additional 20hp and 9.6 lb-ft at the wheels. (Total: 255.9 hp/299.6 lb-ft)