1968 Chevrolet Corvette ZL1 Engine - ZL Wonderful

Mention the ZL1, the original all-aluminum 427ci big-block that only found its way into a pair of '69 Corvettes and a handful of COPO Camaros, and not only are you speaking of the most valuable Corvette engine, but perhaps the most powerful.

Unfortunately, none of us may ever have the opportunity to own, drive, race, or even breathe hard next to a ZL1. So what comes close? How about building one of your own?

That's what John Marshall of Boca Raton, Florida, wanted when he approached us at the Corvette Clinic with his '68 Corvette roadster, not just to drool over for handsome, lightweight good looks, but ultimate power potential.

John wanted an engine that did its own talking. After all, a Rat motor with side pipes is music to everyone's ears. He wanted a serious horsepower machine, no fancy chrome or polished aluminum. He said, "Keep it clean and smooth."

In the 35 years since the ultimate Chevrolet big-block was wedged into a Corvette, technology has embraced the Chevrolet big-block. Back in the '80s, Donovan Engineering found a niche with an all-aluminum, race-bred engine block that matched the Rat motor architecture with high durability and light weight.

Ever since, Donovan big-blocks have become the rave of drag-racing classes where big cubic inches are in high demand. We wanted to know if an all-aluminum big-block had the same panache in the world of street muscle.

The Latest TechnologyThe Donovan aluminum cylinder block is more than a race block purposely built for the performance aftermarket industry, and we were out to prove that by combining it with a Callies crankshaft with Carrillo H-beam connecting rods.

A custom-built Stef's oil pan was fabricated for oil control under road-race conditions. The Stef's oil pickup was also custom built for the oil pan. We used a GM big-block Gen V starter for its high torque and compact size-a must when considering oil-pan fabrication.

A Crane PowerMax hydraulic roller camshaft with 0.632 inch of lift, and 306 degrees intake and 318 degrees exhaust duration at .004 tappet lift was used to set the valvetrain in motion. An adjustable timing gearset was used to set cam timing.

Brodix cylinder heads and Crane 99896 valvesprings with 132-psi (closed) and 414-psi (open) spring pressure control the titanium valves. Jesel shaft-mounted rocker arms were used for valve actuation. Custom-length Crane pushrods and roller hydraulic lifters wrapped up the long-block.

One big concern was the production of high torque output at low engine speeds. Arizona Speed and Marine has a Vortec-style big-block intake manifold with large intake runners and plenum. So the ASM intake was used for air distribution with a 58mm throttle body for control.

The final question concerned fuel and ignition control. We wanted the latest technology in fuel control, which seemingly changes every hour. The decision was made to use Electromotive for fuel control because its TEC3 system has sequential fuel-injector control and interfaces with its digital ignition control.

The Electromotive control module also controls optional electric cooling fans, nitrous systems, and timed accessories. The Electromotive ignition system uses coil-per-cylinder technology with a crankshaft-mounted timing wheel. Tuning is handled with a laptop computer and can be done on the fly, which simplifies engine setup for everyday driving.

Once the engine is installed, more tuning will be necessary and will be discussed in depth in future issues.

Computer TuningSetting up a fresh engine with electronic controls can be interesting. Once a baseline is set, power runs can be performed. The engine was sent to ACME Machine Shop in Plant City, Florida, for dynamometer testing. Rob Reese at Extreme Turbo Shop, an authorized Electromotive dealer and tuner, oversaw the test.

After a few hours on the dyno, Rob called to report the engine was making 607 hp and going into a vacuum at wide-open throttle. We decided the intake had the desired flow characteristics, but a larger throttle body was necessary.

A phone call to ASM confirmed the intake system could handle a larger-cfm throttle body. Arizona Speed and Marine offers a bolt-on 1,325-cfm mono-blade throttle body. It was sent to Extreme Turbo in Lakeland, Florida, and Rob removed the top of the intake and machined out the center of the intake opening to fit the mono-blade throttle body.

After a few dyno runs to set up the programming for the throttle-body change, the monster Donovan engine made 657 hp at 5,200 rpm with 678 lb-ft of torque at 4,800 rpm.

The throttle body was well worth the $500 investment with a 50hp gain. The ASM intake system with the Electromotive TEC3 fuel/ignition system made impressive torque numbers immediately.

So, we have 600-plus horses to transmit through a Richmond six-speed transmission with C4 suspension. Is that too much for the street? We discussed two programs with Rob: pull out some ignition timing for driveability and install a Saturday night kill mode. Now we will proceed with assembly and further testing.