C3 Big-Block Engine Swap - Big-Block Party

Part 2 was a step-by-step build plan showing how, with the help of a select list of high-performance suppliers, we assembled this 21st century Rat motor.

This month, we'll install all the new upgrades we've chosen, along with the main ingredients of our project—specifically, the engine, a super-duty Gearstar 4L60E transmission, and a made-to-order, bulletproof rearend from Precision Corvette Differential.

There's a learning curve with every "first-ever" build, and it quickly became apparent that our C3's stock automatic transmission didn't have a chance of handling the new big-block's output. So we switched to a Gearstar Level 4 electronically controlled 4L60E/four-speed automatic. It has an 11-inch, custom-stalled, full-billet, lock-up torque converter, and it's built to handle up to 650 hp and 600 lb-ft of torque. Follow along now as we find out what it takes to get a transmission to Level 4 capability.

A Complete Trans-Formation
Gearstar Performance Transmissions says it "custom builds your transmission to order." Fortunately, that's a fact and not just a slogan. Much as you would when having a bespoke suit made, you'll speak directly to one master tech, who will then build your transmission—based on your specific requirements—from start to finish. The journey to building a Level 4/4L60E starts with qualifying the case, then high-pressure washing and bead-blasting it. It's then re-washed, re-inspected, and painted.

To handle the additional torque, Gearstar uses a high-capacity pump with a hardened rotor and vanes. The input drum is hardened and reinforced with a billet sleeve to greatly increase strength, and the clutch drum is also modified, allowing it to tolerate higher rpm levels. Additional clutches and steels are added, which boosts clutch capacities by 30 percent. The Level 4/4L60E also incorporates a fully rollerized planetary gearset that provides enhanced durability and greatly reduces power-robbing drag. The four-pinion OE planetaries are replaced with hardened five-pinion steel planetary gearsets.

This Level 4/4L60E is one of the most flexible fully electronic transmission packages available, allowing us to completely customize shift timing, shift feel, and lock-up application. The bottom line is that every part of the transmission is brought up to super-duty specs so it can handle the power and deliver years of trouble-free service. And Gearstar guarantees every transmission it sells. Welcome to Level 4.

Once we had our upper and lower control arms coated, we were hooked. We ended up powdercoating the entire front suspension, the trans crossmember, the rear-diff crossmember, and a few other odds and ends. Miller's can even powdercoat your entire chassis in virtually any color you'd like.

Now that our chassis was cleaned and painted, and our front suspension powdercoated, we were loath to reinstall the stock power-assist slave cylinder. It's always leaked, and we were told that a new stock-replacement unit would end up in the same condition in just a few months. The best remedy was to upgrade to a new Borgeson power-steering box. It offers better road feel, a quicker turning ratio, and eliminates the slave cylinder completely. The Borgeson kit is complete and includes the hoses, lines, and a new rag joint as well. The installation was straightforward and, best of all, uneventful.