Click for Coverage
Exclusive Content
Original Shows, Motorsports and Live Events
Try it free for 14 days
Due to the EU’s Global Data Protection Regulation, our website is currently unavailable to visitors from most European countries. We apologize for this inconvenience and encourage you to visit for the latest on new cars, car reviews and news, concept cars and auto show coverage, awards and much more.MOTORTREND.COM
  • JP Magazine
  • Dirt Sports + Off-Road
  • 4-Wheel & Off-Road
  • Four Wheeler

GM Performance Parts 502 Torque Motor Buildup

Posted in How To: Engine on September 1, 1998
Share this

An engine buildup usually targets a specific need: A trail 4x4 needs an engine that will idle all day long and produce torque down low; a mud truck needs lots of horsepower, and it's fine if the engine has to turn a high rpm to make that power; and a tow rig needs lots of power but with low compression to avoid detonation. It's rare when one engine can fit all these requirements.

At least that's what we thought at the onset of a recent 502 engine buildup. But then we looked at what we were starting with and what is available for a big-block Chevrolet engine, and realized that this is it-the omni-engine.

GM Performance Parts offers 502s in a few varieties. The off-road 502 truck-conversion engine (PN 12371054) makes 338 hp and 512 lb-ft of torque, and the Gen VI H.O. 502 (PN 24502620) makes 450 hp and 550 lb-ft of torque. An H.O. 502 comes with better cylinder heads and camshaft than the truck-conversion engine. It's also more complete than the conversion engine, including an intake manifold, a water pump, and a flexplate. From this engine, you can build anything from a brute-torque daily driver and off-road engine up to a full-blown competition powerplant-all using the same short-block. This allows you to start now with a complete crate engine and build it over time to fit your desires.

GM Performance Parts also offers two engine kits; the 502/502 base engine kit (PN 12371204) starts with an assembled short-block and includes oval-port heads, valvetrain, and valve covers to make 502 hp and 567 lb-ft of torque, while the 502/502 premium kit also includes the intake, carb, water pump, starter, and ignition system. You can also buy just a 502 short-block (PN 24502619).

Our Plan
We started with a GM Performance Parts Gen VI H.O. 502 and made bolt-on changes to produce two more potent-power combinations. With its massive displacement, the H.O. 502 engine is a darn impressive engine right out of the crate-a fact we verified by dyno-testing one fresh from the GM parts counter. The GM Performance Parts catalog (which is available at your local dealer or can be downloaded from the GM Performance Parts Web site free of charge) claims the H.O. makes 450 hp at 5,250 rpm and 550 lb-ft of torque at 3,500 rpm.

We began our powerful adventure with a new Gen VI H.O. 502 from GM Performance Parts. It comes with iron, rectangle-port heads, an aluminum dual-plane intake, a damper, a water pump, and a flexplate. Inside the short-block is a steel crank and forged pistons along with a hydraulic roller cam (211/230 degrees at 0.050 and 0.510/0.540-inch lift).

Leafing through the GM Performance Parts catalog revealed a pair of rectangular-port aluminum heads (in addition to oval-port heads) and the roller camshaft used in the 502/502 engines. While traditional thinking is that oval-port heads make better low-end power at the expense of a few horsepower, we decided to try the new rectangle-port heads (in fact, all three cylinder heads used on this engine were rectangle-port) with the 502/502 cam. For this combination, we used an Edelbrock Performer RPM, a Holley 750 double-pumper, Crane Hi-6 ignition, 2-inch Hedman headers, and 2 1/2-inch exhaust with Flowmaster 50-Series, three-chamber mufflers.

If this version isn't calling your name, there's still more power you can build with the stock short-block. We experimented with a pair of iron Merlin VR Race cylinder heads from World Products and a Crane Street Roller camshaft and then added other components that become necessary at higher-power levels, such as an Edelbrock 454-R intake, a Jones Performance carburetor, Manley valves, and a Milodon oil pan. The result was plenty of power to turn 44s or anything smaller through even the worst gumbo. Even though this last variation of the 502 is more of a competition engine, the parts were chosen so that it could live on the street and still run on pump gas.

The Outcome
You can stuff a big-block Chevy into nearly any 4x4 (we've even seen them in Jeeps), and we've shown just three versions of this venerable engine. Because of its displacement, a very mild 502 will produce gobs of torque that any off-road vehicle can use. And, whether you know up front or decide after a few years of use, the same 502 can be built to meet nearly any power need.

PhotosView Slideshow

Three Delicious Favorites
While there are countless ways to build a 502, here are the dyno results from the three we show in this article. All testing was conducted in Flowmaster's R&D dyno cell operated by Kevin McClelland and John Wilson.

Version One: An out-of-the-crate H.O. 502 with a 750 Holley carb, 2-inch Hedman headers, 2 1/2-inch exhaust and Flowmaster mufflers, and a GM HEI distributor.

rpm Torque Horsepower
2,000 478.3 182.1
2,250 479.0 182.1
2,500 495.6 235.9
2,750 521.9 273.3
3,000 543.8 310.6
3,250 547.9 339.0
3,500 541.0 360.5
3,750 535.6 382.4
4,000 524.7 399.6
4,250 512.8 415.0
4,500 505.0 432.7
4,750 485.5 439.1
5,000 467.8 445.4
5,250 446.9 446.7
5,500 412.1 431.6

Version Two: A 502 with GM Performance Parts aluminum rectangle-port heads, a 502/502 camshaft, an Edelbrock Performer RPM manifold, an 850 Holley carb, 2-inch Hedman headers, 2 1/2-inch exhaust and Flowmaster mufflers, a GM HEI distributor, and Crane Hi-6 ignition.

rpm Torque Horsepower
2,000 496.5 189.1
2,250 485.1 207.8
2,500 509.2 242.4
2,750 544.5 285.1
3,000 546.5 322.3
3,250 565.5 349.9
3,500 563.9 375.8
3,750 561.6 401.0
4,000 552.4 420.7
4,250 541.7 438.4
4,500 541.1 463.6
4,750 529.8 479.2
5,000 529.8 488.5
5,250 495.8 495.6
5,500 478.7 501.3
5,750 450.3 493.0

Version Three, Pt. I: A 502 with Merlin VR Race heads, an Edelbrock Victor 454-R manifold, a Crane 260 SR camshaft, a Jones Performance 750 Dominator carb, Crane Hi-6 ignition, 2 1/4-inch Hedman headers, and 4-inch exhaust with Top 10 Shootout 40-series race mufflers

rpm Torque Horsepower
4,000 537.0 409.0
4,250 535.9 433.7
4,500 539.1 456.8
4,750 555.6 502.5
5,000 578.5 550.7
5,250 590.1 589.9
5,500 589.0 616.8
5,750 580.9 636.0
6,000 568.3 649.2
6,250 557.6 663.6
6,500 528.4 654.0
6,750 503.3 646.9

Version Three, pt. II: A 502 with Merlin VR Race heads, an Edelbrock Victor 454-R manifold, a Crane 260 SR camshaft, a Jones Performance 1050 Dominator carb, Crane Hi-6 ignition, 2 1/4-inch Hedman headers, and 4-inch exhaust with Top 10 Shootout 40-series race mufflers

rpm Torque Horsepower
4,000 549.2 418.3
4,250 546.3 442.0
4,500 544.4 466.5
4,750 572.7 518.0
5,000 573.7 546.2
5,250 591.7 591.5
5,500 593.8 621.8
5,750 584.4 640.0
6,000 577.0 659.2
6,250 567.3 675.1
6,500 545.1 674.6
6,750 516.0 663.1

All the Parts
Product Source Part No.
Merlin head studs ARP 235-4016
Big-block damper bolt kit ARP 135-2501
5/16-inch carb studs (short) ARP 200-2401
262/270 Street Roller camshaft Crane 16SR00001
Roller lifters Crane 13552-16
8.250- and 9.250-inch pushrods Crane 13640-16
1.70:1 Gold roller rockers Crane 13750-16
Quick-Lock valvetrain stabilizer Crane 13602-1
7/16-inch rocker studs Crane 99153-16
Guide plates Crane 13650-1
Hi-6 ignition box Crane 6000-6420
FireWire 8.5mm 90-degree boot plug wires Crane 250-0082
Performer RPM Edelbrock 7163
Victor 454-R Edelbrock 2907
Head gasket Fel-Pro 1047
Intake gasket Fel-Pro 1211
Valve-cover gasket Fel-Pro 1630
2 1/2-inch mufflers Flowmaster 42553
4-inch Top 10 Shootout mufflers Flowmaster 54040-10
Gen VI H.O. 502 GM Perf. Parts 24502620
HEI GM Perf. Parts 1104067
High-torque mini starter GM Perf. Parts 12361146
Cast-aluminum Chevrolet-script valve covers GM Perf. Parts 12371244
1.70:1 roller rockers GM Perf. Parts 1236123
Oil pan Milodon 30955
Pickup tube Milodon 18301
Oil pan studs Milodon 81305
750 Dominator Jones Performance n/a
1050 Dominator Jones Performance n/a
Clevite 77 rod bearings Number 1 Performance CB-743P
Clevite 77 main bearings Number 1 Performance MS-829P
Hi-Tech cam bearings Number 1 Performance BC616S
Iron Merlin VR Race heads World Products 3063A


Flowmaster Inc.
Santa Rosa, CA 95401
Crane Cams
Daytona Beach, FL 32117
Comp Cams
Memphis, TN 38118
World Products
Ronkonkoma, NY 11779
Chevrolet Performance Parts
Detroit, MI 48232
JET Performance Products
Huntington Beach , CA
Number 1 Performance
RPM Engines & Machines
Ronhert Park, CA 94928

Connect With Us

Newsletter Sign Up

Subscribe to the Magazine

Browse Articles By Vehicle

See Results