Although GM has been building and selling crate engines to the general public for years, many of its offerings have hardly been what we'd call "High Performance." Sure, they were good engines. But what they had in quality, they lacked in gusto. Not anymore. GM Performance Part's (GMPP) newest line of crate big blocks is a classic example of racetrack power transcending to the street. We're talking about GMPP's two new big-block Chevy crate engines. Each totaling 572 cubic inches with one for the street and one for the track, or maybe two for the street if you're not against lashing valves and driving around breathing race gas fumes.

The coolest things about either one of these crate engines is that after you've bought one, you don't have to do a thing, that is, except to drop it in your car and fire it up. They come delivered to your door already broken-in with all the necessary fixin's to get you under way. There's very little else you'll need to buy to make these beasts run. Of course, you'll need the standard items like fuel and oil, but you won't have to buy spark plugs or ignition cause it's already in there. Also, both of these engines come with roller cams; a hydraulic roller in the street engine, and a solid roller in the race engine, so there'll be no cam break-in needed either. Both engines even come with their own carb that's already dialed in. Although you may have to adjust it some, depending on where you live and your local weather conditions. But for the money, these things are really hard to beat. And don't think for a minute that these engines are some old rebuilt Rat motors. Every part used in these beasts is 100 percent new and very heavy-duty to boot.

When GMPP set out to build the baddest crate engines around, they sparred no expense ensuring that the engines would live to fight for a long, long time. To that extent, GMPP equipped both big-blocks with 4340 forged steel cranks and rods. Forged aluminum pistons with full-floating wrist pins were also included, 9.6:1 compression for the street motor and 12:1 on the race version. And both engines have roller cams for power and durability. On top of that GMPP installed a new version of its proven rectangle-port aluminum cylinder heads, and then cast up a special single-plane intake manifold to fit the tall-deck Bowtie Sportsman Gen VI block. And to make sure there'd be no chance of any one of these engines not making the power they claim, GMPP installs its own specially made Demon double-pumper carb and a hi-perf HEI complete with wires and AC plugs.

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."

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
RPMTorque 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
GMPP GM Performance Parts Westech Performance Group
11098 Venture Dr., Unit C
Mira Loma
CA  91752
  • «
  • |
  • 1
  • |
  • 2
  • |
  • View Full Article