GMPP'S LITTLE SECRET?
We asked the guys at GM Performance Parts why their engine that's rated to make only 620 hp and 650 lb-ft of torque could crank out 13 percent more horsepower and almost 10 percent more torque on our dyno test? Did they send us a ringer? We demanded an answer!
"The engine is under-rated because we correct the dyno measurements using the SAE (Society of Automotive Engineers) correction factor, rather than the aftermarket standard correction factor." GMPP responded. "Further, we under rate slightly to ensure that a customer can always meet our claimed power numbers if he installs one of our engines on a dyno, no matter which correction factor is used."
POWER TO SPARE
When we bolted this engine onto Westech's Superflow 901 dyno, we were expecting it to make at least as much as GMPP's claimed it would; 620hp and 650lb-ft of torque. What we were not expecting was to eclipse those figures by such a huge amount! Even after GMPP told us the reasons that its engine made so much extra power (see: "GMPP's Little Secret?"), we were still floored. Could this actually be better than its advertisements claim it is? You can bet your checkbook that it is. Because this thing cranked out so much more power, our first thought was that GMPP sent us the race motor instead. But, a quick reality check told us that if it was the race engine, there's no way it would still be running considering we were only feeding it 91-octane pump gas. So we pulled the valve covers to check for valve lash, which there was none. And a quick peek down at the lifter valley confirmed that this engine was running GMPP's hydraulic roller lifters. We guess that with so many cubic inches on tap the right combination of parts can make tons of extra power.
|Dyno Results |
|RPM||Torque ||Power |
|Bore: ||4.560" |
|Stroke: ||4.375" |
|Compression: ||9.6:1 |
|Block: ||GMPP Sportsman tall-deck Bowtie Gen VI, 10.2-inch deck |
|Crank: ||forged 4340 steel, internally balanced |
|Rods: ||6.535-inch 4340 steel, H-beam |
|Pistons: ||4032-T6 forged aluminum w/ floating wrist pin |
|Rings: ||Plasma-moly |
|Cam: ||hydraulic roller, 254/264 duration @ .050, .632 valve lift |
|Heads: ||GMPP aluminum rectangle port, PN12499255, 118 cc chamber, 315cc intake runners |
|Valves: ||stainless 2.25-inch intake, 1.88 stainless exhaust |
|Lifters: ||GMPP hydraulic roller |
|Rockers: ||GMPP aluminum roller 1.7:1 ratio |
|Manifold: ||GMPP single plane |
|Carb: ||850cfm Demon double pumper |
|Ignition: ||GMPP HEI |
|Plugs: ||AC R42XLS |
|Fuel: ||91+ octane required |
|Oil: ||20W-50 recommended, 7-qt. system capacity |
|Valve covers: ||GMPP cast aluminum |
|H2O pump: ||GMPP aluminum |
|Dampener: ||GMPP steel |
|Color: ||What else could it be? Chevy orange |