A long time ago, in a magazine far, far away, we built a Corvette project car designed to incorporate a state-of-the-art powertrain with a C4 chassis. It came to be known as Project C4orce, and it progressed with little more than standard project-car delays and frustrations. To a point. Then Mr. Murphy and his law ("Anything that can go wrong, will go wrong") stepped in with a vengeance. Suffice it to say, once "Darth Murphy" appeared, "The Force" was definitely not with us. I'll spare you all the gory details that led to one delay after another, and move on to the final chapter, after a brief recap.
The original series launched in Corvette Fever magazine, which was merged into VETTE earlier this year. Our plan was to update an '87 C4 with an LS-based powerplant and a five-speed Tremec transmission, and to spend less than $15,000 (including the cost of the car) to complete the project. It's certainly possible to do that-if you're not trying to serve the dual masters of project completion and editorial coverage. Obviously, anyone attempting to duplicate our project will have to address issues unique to the vehicle with which they're working. In attempting to cover as many of these issues as we could, it appeared that our budget was spinning out of control. In fact it wasn't, because many of the modifications we made were not required by our particular project vehicle; we included them because it was reasonable to expect that they would be required on other C4 project candidates.
As can be seen in the accompanying photos, Project C4orce was ultimately "dressed" with a unique paint scheme designed by Murray Pfaff of Pfaff Designs in Royal Oak, Michigan. Complementing the paint is a set of C6-style Sport Edition V6 wheels and Dunlop Sport 9000 tires from the Tire Rack. Interior upgrades include unique C4orce leather upholstery and plush carpeting by Mid America Motorworks, along with an analog instrument panel from VettAid.
Beneath Project C4orce's hood is a 5.3-liter LS-style engine that spent its former life in a Silverado pickup truck. Our initial decision to use this mill, as opposed to an LS1 or LS2, was prompted by economics. We purchased a complete engine, including all accessories, PCM, and wiring harness, for $700. Some readers criticized this choice as being a step backward because we were replacing a 5.7-liter (L98) engine with one of less displacement. The point that these readers missed is that if we had made no modifications at all to the 5.3, we still would have picked up 45 horsepower (the factory ratings for the 5.3- and the original 5.7-liter TPI engines are 295 and 240, respectively).
With surprisingly few modifications, 5.3-liter engines can crank out enough power to bring a smile to the face of any Corvette owner. But before a "truck" engine can be installed in a C4 chassis, a few changes have to be made. On the top side, the relatively tall truck intake manifold and high-mounted accessories will poke large, ugly holes in the hood, should you attempt to close it. On the lower end, truck-style oil pans are much too deep for a Corvette's low stance. The easy solution is to install an LS1 or LS6 intake and an accessory bracket, water pump, vibration damper, and oil pan originally designed for a C5 or F-body (Camaro/Firebird).
That's precisely what we did. We also added a set of 1 3/4-inch, coated tubular headers from Melrose Motorsports that were specifically designed to fit LS-style engines installed in C4 chassis. The balance of the car's exhaust system consists of a Random Technology high-flow catalytic converter/X-crossover pipe assembly. This system, which is also available for L98- and LT1-powered C4s, is a true dual system that extends from the header collectors to the mufflers. This arrangement allows virtually any muffler originally designed for a C4 to be used. We added a pair of stainless steel mufflers that provided a deep tone and aggressive sound.
One of the primary modifications made to increase power output is a custom C4orce camshaft ground by Comp Cams. We were more interested in mid-range than top-end power, so we kept duration rather conservative. Rated at 0.050-inch valve lift, this cam has 220 degrees of intake and 224 degrees of exhaust duration. While those specifications might seem extremely mild, the engine's response proved that they're nearly ideal. Low-speed and mid-range driveability are excellent, and there's just enough lope at idle to draw admiring glances from anyone who hears the exhaust.
Additional breathing enhancements are derived from the original 5.3-liter cylinder heads, which were pocket ported by Pete Incaudo of VMax Motorsports. Owing to the budget constraints of the project, Incaudo elected to do a mild port clean-up and precision valve job rather than a full CNC port modification. After installing the modified heads, we added an LS6 intake manifold, which we fortunately had left over from another project. The final piece to our intake system puzzle is a CNC-modified throttle body from VMax.
While an LS6 intake manifold is preferable for any performance-oriented engine, it's certainly not essential. The LS1 manifolds found on '97-'00 model-year engines are perfectly acceptable. While they might not provide the LS6's ultimate power potential, their cost makes them extremely attractive. Used manifolds in excellent condition are available for $30 or less.
The final piece in the puzzle of bringing a transplanted LS-style engine to life is the electronic engine controller, which must be reprogrammed to function in an environment that's dramatically different from the one in which it formerly operated. The required changes are readily made with FlashScan software from EFILive. We opted to eliminate the mass-airflow sensor from the Project C4orce engine installation, so the first order of the day was to convert the PCM to operate in speed/density mode. We also had to turn off some of the diagnostic tests (because they were no longer applicable) and reconfigure the tables that control fuel delivery and ignition settings.
Idle and part-throttle operation are typically the most time-consuming aspects of reprogramming an ECM or PCM for a modified engine. Fortunately, the testing required to optimize these settings doesn't require a chassis dyno. (In fact, it can't be done on a chassis dyno, unless the unit in question has the capability of operating in steady-state mode.) Wide-open-throttle operation is a different matter entirely, so after finalizing the idle and part-throttle settings, we headed to Atlanta Chassis Dyno for a maximum-power test session.
Considering the engine's displacement, camshaft, and cylinder heads, we were expecting maximum hp to fall in the 300-325 range. To our surprise, the engine cranked out 349.75 horses at 5,800 rpm and peak torque of 336.17 lb-ft at 4,800 rpm. The peak-torque figure was in the middle of a broad, flat curve that exceeded 310 lb-ft from 3,500 to 5,800 rpm. (These figures incorporate the SAE [net] correction factor.)
If you're used to looking at the torque curves of tuned port engines, you'll notice that the 5.3's torque peak is achieved at relatively high rpm. That's a characteristic of LS-series engines. A completely stock 5.3-liter engine, with an absurdly mild camshaft (190 degrees of duration measured at 0.050-inch lift) produces peak torque at 4,000 rpm. It's also worth noting that a stock LS1 only produces about 300 hp at the wheels, while an ('02-'04) LS6 cranks out around 355.
In spite of the exceedingly long time it took to complete Project C4orce, the results are gratifying. They also provide a blueprint for anyone wishing to undertake a similar project. Whether the engine of choice is a 5.3-, 5.7-, 6.0-, 6.2-, or 7.0-liter model, the basic mechanical steps are the same. And the end result will be a truly unique Corvette.