Subscribe to the Free

GM Performance Parts ZZ572 Power Curve - Power Moves

Raising the Power Curve of the ZZ572

Bob Mehlhoff Jun 1, 2004
148_0406_572_lead_z 2/12

We began with the GM 572/620 HP in its out-of-the-crate configuration. To that we added 2-inch primary headers with 3-inch collectors connected to 3-inch dual-exhaust pipes, 3-inch balance tubes, and Super 40 mufflers.

We hot rodders love numbers. Whether it's e.t., miles per hour, torque, or horsepower, in our world of extreme automotive performance, everything is measured or interpreted with sexy figures (uh, the mathematical kind). As gearheads know, there's no substitute for big cubic inches, so when Chevy recently unleashed its largest and most powerful street engine, the ZZ572/620, the hot rodding world took notice. Based on a new Gen VI tall-deck Bow Tie block, the ZZ572 is fitted with a forged-steel crankshaft, a 4.375-inch stroke, and forged-aluminum pistons with full-floating wristpins. With redesigned aluminum rectangular-port cylinder heads, 2.25-inch intake valves, and a big hydraulic-roller camshaft yielding 0.632-inch lift and 254/264 degrees of duration at 0.050, the giant Rat easily surpasses the factory-rated 620 hp at 5,500 rpm and 650 lb-ft of torque at 4,500 rpm. But even with such a hefty stroke, the ZZ572's long-duration camshaft skews the mammoth power to the upper-rpm range leaving it with a ratty idle quality. If you've been reading CHP for some time, you know our Performance Q&A guy Kevin McClelland loves a tuning challenge. When McClelland and the crew at Flowmaster recently set out to dyno and wrench on a Burt Chevrolet-supplied GM ZZ572/620 to improve the motor's performance manners, we couldn't pass up the chance to help. The performance mission was to refine the ZZ572's power curve to deliver more usable torque with a small selection of existing GM parts, a good street intake manifold, and a healthy Flowmaster 3-inch exhaust system fitted with new Super 40 mufflers.

Our crowd of gearheads included Flowmaster's dyno man John Wilson, Burt Chevrolet GM Performance Parts Manager Ken Casey, and yours truly. The mission was clear: We didn't want to lose any of the ZZ572's incredible performance, but we wanted to increase and raise the torque curve across the rpm band. As performance folks understand, big, wide torque curves produce impressive acceleration.

148_0406_572_2_z 3/12

On the ZZ572/620's baseline dyno run, the engine delivered 649.1 lb-ft of torque at 4,800 rpm and 647.9 hp at 5,700 rpm. For our evaluation, we focused on improving the torque numbers and the shape of the torque powerband.

Test I
As delivered from Burt Chevrolet, the GM tall-deck motor included a Demon 850-cfm carburetor, an MSD distributor, and a GM open-plenum aluminum intake manifold. To that we added headers with 2-inch-diameter primary pipes, and a Flowmaster 3-inch exhaust system with H-pipe and the Super 40 (PN 953046) mufflers. After bringing the motor (in delivered trim) up to operating temperature, the torque peaked at 649.1 lb-ft at 4,800 rpm and the horsepower was 647.9 at 5,700 rpm.

Test II
We knew by the baseline numbers that we could improve upon the torque reading. First, we axed the open-plenum intake (largely designed for peak power numbers) in favor of a dual-plane Edelbrock Air Gap Performer RPM. We especially like the Edelbrock piece because it works well in the midrange rpm scale. But because the ZZ572 is a tall-deck design, we needed Moroso intake manifold spacers to facilitate the installation. We fired the motor to stabilize temperatures and ran the engine up to speed to record the data. Yow! The Edelbrock manifold raised and widened the midrange torque band considerably. Peak torque was 641.7 at 4,400 rpm, but more importantly, the entire torque curve with this manifold improved by as much as 60 lb-ft at 2,000 rpm over the existing GM open-plenum intake.

148_0406_572_3_z 4/12

To broaden the torque curve, we removed the existing open-plenum aluminum GM intake and added an Edelbrock Performer RPM Air Gap. Because this engine is a tall-deck design, the cylinder heads are spaced farther apart, which required Moroso intake-manifold spacers.

Test III
For our next attack, we wanted the benefits of a shorter-duration camshaft. From the Burt Chevrolet parts bins we selected the 450/502 H.O. 450hp hydraulic roller (PN 24502611) that features 211/230 degrees of duration at 0.050-inch lift and 0.510/0.540 lift. To make certain that we had our camshaft data correct, McClelland degreed-in the bumpstick and found that it installed at a 110.25 intake lobe centerline. Then we installed the remaining components and fired up the King Rat. McClelland set total timing at 33 degrees. With the engine making all the right sounds, torque improved to 663.4 lb-ft at 3,700 rpm. What's more, the torque at 2,000 rpm climbed to 595.2 lb-ft compared to our baseline plot of 468.7 lb-ft at 2,000 rpm. Even better, the engine now had 19 inches of manifold vacuum at 800 rpm up from 8 inches at 1,000 rpm with the factory engine configuration.

By making a few simple changes to an already powerful package, we now had an engine that would idle easily in traffic and produce tremendous midrange power--just what street cars thrive on. For our testing, we ran 91-octane unleaded. Because a street engine is operated below peak power numbers, raising the torque curve across the rpm range improves performance. These modifications are easy to do and the parts are readily available. The same principles can be applied to smaller engines too. Keep the camshaft duration to a moderate level and choose a good street carburetor and pair it with a divided-plenum intake manifold. The results will keep you in the curve.

The Tests

Here's how the 572 measured up in stock trim:

Horsepower: 620 @ 5,500 rpm
Torque: 650 lb-ft @ 4,500 rpm
Compression ratio: 9.6:1
Block: New Sportsman tall-deck Bow Tie Gen VI, 10.200-inch deck height
Bore: 4.560 inches
Stroke: 4.375 inches
Crankshaft: Forged steel
Camshaft: Hydraulic roller
Valve lift: 0.632/0.632 inch
Duration at 0.050: 254/264 I/E
Cylinder heads: Aluminum, rectangular port
Intake valves: 2.25-inch stainless steel
Exhaust valves: 1.88-inch stainless steel
Rocker arms: Aluminum roller rockers, 1.7:1 ratio
Intake manifold: Aluminum tall-deck single-plane
Carburetor: 850-cfm Barry Grant
Ignition: MSD HEI @ 36 degrees total

Test 1 - Our ZZ572 as delivered from GMPP produced 649 lb-ft of torque at 4,800 rpm and 648 hp at 5,700 rpm.
Exhaust: 2-inch headers, 3-inch Flowmaster dual exhaust with H-pipe and Flowmaster Super 40 mufflers.

Test 2 - We broadened the torque curve by replacing the open-plenum GM intake manifold with an Edelbrock Performer RPM Air Gap (PN 7562).
Exhaust: 2-inch headers, 3-inch Flowmaster dual exhaust with H-pipe and Flowmaster Super 40 mufflers.

Test 3 - After installing the 454 H.O./502 H.O. steel-roller camshaft (PN 24502611) with 211/230 degrees of duration at 0.050-inch lift, we generated an incredible 663 lb-ft of torque at 3,600 rpm. Sure, peak horsepower dropped, but all this torque could move a freight train. Maximum camshaft lift with the 1.7:1 rocker ratio is 0.510/0.540 and we ran 33 degrees total advance.
Exhaust: 2-inch headers, 3-inch Flowmaster dual exhaust with H-pipe and Flowmaster Super 40 mufflers.

148_0406_572_16_z 12/12

The Sound of Power

For an engine as powerful as the 572, Flowmaster would commonly recommend 31/2-inch-or-larger dual exhaust. The new Super 40s are so efficient at getting spent exhaust gases out of the engine that we only lost 3 peak horsepower going from open headers to 3-inch Super 40s. For our initial test, the engine baselined with open headers at 651 hp, and we only gave up about 3 hp to 648.5 with full 3-inch exhaust.

The new Flowmaster Super 40s are offered with 21/4-inch, 21/2-inch, and 3-inch inlet and outlet sizes in all offsets. Also available are dual outlets on the 21/2 and 3-inch models. The Super 40s offer the most aggressive, deepest-sounding street two-chamber ever released by Flowmaster.

The Flowmaster Super 40 5x10-inch case is modeled after the Top Ten Street/Race muffler. For our ZZ572 dyno-testing, we used a 3-inch Flowmaster exhaust system and Super 40 mufflers. To learn more about these hot-sounding and free-flowing new mufflers, visit


Moroso Performance Products
Guilford, CT 06437
Barry Grant Fuel Systems
Dahlonega, GA



Connect With Us

Get Latest News and Articles. Newsletter Sign Up

sponsored links

subscribe to the magazine

get digital get print