When we selected a Chevrolet Corvette ZR1 twin-cam, small-block 350 V-8 engine for our Cimtex Rods Super Cameo, we knew that we would be breaking new ground in the sense that GM never built a “production” automatic-transmission-equipped Corvette ZR1. However, there is record that a couple of Corvette ZR1s were specially equipped with automatic electronic overdrive transmissions for physically challenged Corvette enthusiasts. We don’t know whether it was done by the factory or by the private sector. 

Nonetheless, it was our intent to run an automatic transmission behind this awesome powerplant. After all, we wanted our ’56 Super Cameo to be as civilized as possible, yet still be able to handle all the available torque and horsepower that will be the result of this twin Powerdyne (BD11-A) supercharged and intercooled Corvette ZR1 engine. But what type of GM automatic transmission would we actually be using? 

Since the ZR1 engine is fully electronically controlled, we certainly were not going to use a non-electronic trans, so that ruled out a GM TH350 or TH400. Then, too, we definitely didn’t want to use a GM 700R4, as it is fairly limited in the torque and horsepower department. So that narrowed down the selection to a GM 4L60E or its bigger brother, the GM 4L80E four-speed electronic overdrive transmission. Thankfully we had performance transmission specialist “Jimmy G” Galante from Sun Valley, California’s G Racing & Performance Transmissions, also known as www.RaceTrans.com, on hand to point us in the right direction. Not surprisingly, Galante favored the GM 4L80E for this project.

“The GM 4L80E four-speed electronic overdrive transmission came out in 1991,” said Galante. “This transmission is a true four-speed automatic with overdrive, featuring an electronic lockup torque converter. Rated at 440 lb-ft of torque, this transmission was mainly designed for use in GM’s 3500 series truck line (featuring a 2.48:1 first gear, a 1.48:1 second gear, a 1.00:1 third gear, a .75:1 fourth gear and 2.07:1 reverse) as well as medium purpose vehicles (MPV) such as the GM step vans and box trucks, along with Isuzu delivery vehicles and the like. As such, the GM 4L80E is definitely the brute of the GM electronic overdrive automatic transmission family!” But how does the GM 4L80E differ from its 4L60E counterpart? 

“At approximately 170 pounds, the GM 4L60E is a much smaller and lighter transmission, and it was primarily designed for passenger car and light-duty truck use. Due to its compact nature, the 4L60E gets its electronic overdrive feature by overdriving low gear to get second gear. Then it overdrives third, or high gear, to achieve the overdrive gear. Conversely, the GM 4L80E, which weighs approximately 260 pounds, physically has an actual overdrive gear located right on the front of the input shaft. Due to its case construction, this transmission is much stronger and more conducive to heavy-duty load applications. Most of your light-duty gas and diesel truck applications, which utilize the GM 4L80E, produce somewhere in the range of 350 hp and 440 lb-ft of torque.” Now let’s compare the GM 4L80E to the GM TH400. 

“The GM 4L80E is often referred to as being a GM TH400 with an overdrive added to it,” says Galante. “With the exception of the aforementioned overdrive gear being located in the front of the input shaft (on the 4L80E), from there back the transmission does resemble a GM TH400, with two drums (forward and reverse) and a non-drive-shell planetary drive gear system with its sun gear tube. In fact, various pre-1997 TH400 planetary gear system components, such as the reaction carrier and the output carrier, are totally interchangeable (with minor modifications) between the GM TH400 and the GM 4L80E. However, there have been some internal improvements made to the GM 4L80E for the sake of convenience and smoother operation. One of the things the GM TH400s tend to do is slam or clunk in reverse,” says Galante. “With the 4L80E, GM engineers redesigned the transmission fluid circuit (in the valve body) so that it regulates the line pressure when you shift the transmission into the ‘R’ position for a smoother engagement, so no more slamming into reverse.”

Galante went on to say that the GM 4L80E also uses a gear-driven transmission fluid pump instead of a vein pump, because most of the rpm operating ranges in the 4L80E are much lower than those in, let’s say, a GM TH400 or a GM 4L60E, which traditionally get bolted up to higher-rpm engines. “This pump is nice and strong with a big input shaft and a huge stator support. It’s definitely got beef!”

Okay, now that we know we’re starting out with a transmission capable of withstanding heavy torque and horsepower loads, what modifications will www.RaceTrans.com do to the GM 4L80E in order to make it good enough to handle 600-plus horsepower and 650 lb-ft of torque?

“Aside from totally replacing all of the internal components—bushings, O-rings, gaskets, seals, etc.—with a www.RaceTrans.com GM 4L80E rebuilder kit, we’re going to beef up this transmission using a set of Alto Red Eagle clutches (part No. 031750AHPPWR) and a set of Kolene-coated steels (part No. 031721K). We’re also going to tighten up the clearances inside the transmission and then install a TransGo shift kit (part No. 4L80E-HD2). However, in the process, we’re also going to slightly modify the programming to make our 4L80E into a manual automatic. So when you put it in low gear, it stays in low gear. 

“To further enhance the performance of the transmission, we’re going to install a 13-inch stainless steel billet design case with a 2,500-3,000-rpm-stall-speed 10-inch lockup torque converter (part No. 4L60ES4) from The Converter Shop (TCS). This unique setup should totally complement the Corvette ZR1’s .560-inch valve lift and .302-degree-duration dual overhead camshafts.” Since the GM 4L80E is an electronic overdrive transmission, it was also necessary to set up the programming (computer tuning) in order to optimize overall performance without overdoing it. “We selected one of HGM’s CompuShift standalone transmission control systems, and they are totally awesome,” says Galante (see sidebar). 

For openers, the HGM CompuShift transmission control system does not require a laptop computer and other expensive computer software to make changes and read its display. It’s strictly a plug-and-play application. The HGM CompuShift transmission control system features a totally sealed module (available in either standard black wrinkle finish or optional polish), which can be mounted anywhere in the truck and is capable of withstanding high-heat installations. The CompuShift transmission control system also has its own display screen (monitor), which can either be used as a hand-held unit or permanently installed inside your vehicle.

Essentially there is a total of three hookups: The power wire, the ground wire and the throttle position sensor hookup orm in the case of a carbureted car, an adjustable throttle linkage sensor. The HGM CompuShift transmission control system also has a tachometer (rpm input) sensor hookup and can monitor gear ratio, engine temperature and so on. However, the unit does not use the tachometer for actual shifting. You can either preset your shift points to suit your desired specification or install the OE 4L80E transmission control ?program.

For this buildup, we also installed one of PML Incorporated’s finned aluminum, black-wrinkle-finish, deep transmission fluid pans (part No. 9437), which increases the 4L80E’s fluid capacity 3.25 quarts over stock. Will we be using a transmission cooler at this point? Not likely, as our new www.RaceTrans.com GM 4L80E with PML pan and Be Cool four-core aluminum radiator should feature enough cooling capacity on its own. By now you may be thinking that since GM never built an automatic transmission Corvette ZR1, where in the world did we find a fully balanced, six-bolt Corvette ZR1 flexplate? Consider us lucky. When we purchased our ZR1 engine from Ripley, Oklahoma’s RK Machine, owner Rick Kirk, who worked on the original Corvette ZR1 engine/Mercury Marine “Wet Vette” project, came up with an ultra-rare ZR1 flexplate left over from that project. Otherwise it would have had to be custom made.

Follow along as we document the building of our Jimmy G. Galante/Super Cameo GM 4L80E four-speed electronic overdrive transmission. Note: Some of the OE rebuilding procedures—such as installing the bushings, gaskets and O-rings, as well as assembling some of the stock component modules—have already been done for the sake of time. Enjoy, as this was one of the more important steps in this build, so that the complete drivetrain and the vehicle can begin to come together.