Project C4orce was on display...
Project C4orce was on display at Corvettes at Carlisle and at Mid America's FunFest. With open headers, the car drew an immediate crowd every time we started the engine.
It doesn't have any seats. Or carpet. Or door panels. Or doors, for that matter. But it starts and runs. And at Corvettes at Carlisle, it turned heads and raised eyebrows as it made its official debut. "It" is Project C4orce, and, in addition to being the subject of a seminar at Carlisle, it also appeared at Mid America Motorworks' site on the Manufacturers' Midway. Project C4orce was greeted with enthusiasm and curiosity at both locations-gratifying because Trey Hanson and Jody Gregg of Speed Hound Performance burned more than their share of midnight oil finishing up all the last minute details that always bite in a very tender part of the anatomy.
Aside from the inevitable 11th hour adjustments and alterations, Project C4orce has been proceeding fairly smoothly. After Trey installed the Vmax Motorsports-modified cylinder heads and an LS6 intake manifold (that Speed Hound Performance had leftover from a supercharger project), he completed the intake system with a cable-actuated Camaro/Firebird throttle body, which had also been modified by Pete Incaudo of Vmax. Modified (or ported) throttle bodies are available from a variety of sources, but we've found a fair amount of variation in both the quality of the modifications and the results they produce. Pete has a truly unique understanding of air flow, which invariably translates into cylinder heads, intake manifolds, and throttle bodies that offer unrivalled performance. (I'm frequently reminded of that when someone in a uniform asks me for my license and registration.)
To make fuel line plumbing...
To make fuel line plumbing easier, we flipped the fuel rail so the inlet is positioned on the passenger's side (as opposed to the driver's side as it is on a C5).
At this point in time, we don't have actual horsepower numbers because the car isn't in "dynoable" condition, but according to the flow bench, we've got a killer throttle body. Its flow characteristics will definitely allow the engine to take maximum advantage of the performance potential of the new camshaft and cylinder heads.
Considering the vast array of off-the-shelf camshafts that are available, you may be wondering (then again, you may not) why we elected to have Comp Cams grind a special "C4orce profile." Unless your departure from the turnip truck is fairly recent, you're probably well aware that developing a "combination," as opposed to simply choosing components out of a handful of catalogs, is the key to maximum performance. Since our turnip truck days were more years ago than we care to remember, we wanted a cam profile optimized for this particular engine and the conditions under which it will operate.
An LSx engine fits as well...
An LSx engine fits as well in a C4 engine compartment as the original L98. As is obvious in this photo, we replaced the original truck manifold (which is too tall to fit beneath a Corvette hood) with one from an LS6. The coil brackets used on truck engines are different from those installed on car engines, so some adapting has to be done when a Corvette/F-body fuel rail and accessory bracket are installed.
The C4orce camshaft provides...
The C4orce camshaft provides the engine with a nice lope at idle and a broad torque range. In the short drives we've taken in it, the car feels very strong. Even light touches of throttle make the driver feel as if he's about to roll off the milk crate (aka driver's seat).
Pete Incaudo of Vmax Motorsports...
Pete Incaudo of Vmax Motorsports ported the original truck throttle body to provide increased air flow. This particular throttle body just has a rough-cut finish because we were in a time crunch and needed it done quickly. As soon as time permits, we'll send it back to Vmax for final finishing.
Having been bitten by the...
Having been bitten by the injector bug in previous projects, we sent a set of LS1 injectors to Cody Motorsports before installing them. Eliminating questions about actual injector flow capacity simplifies tuning.
Power output is obviously the primary concern, but that has to be tempered by drivability and low-speed torque considerations. One of the most common mistakes people make when selecting a cam is they focus on the "golden ring" of horsepower and never consider they don't have the support necessary to be able to reach up and grab it. It doesn't make any sense to choose a cam that produces "maximum horsepower" yet kills so much low-speed torque that the engine is a dead player at speeds below 5,000 rpm. In addition to making a vehicle unpleasant to drive, camshafts with excessively long duration can actually be a performance liability-by the time an engine reaches the rpm at which the cam starts to deliver significant power, whatever vehicle was in the next lane is long gone.
In the case of our C4orce profile, we kept duration reasonably short, but selected lobe designs with exceptionally fast opening and closing rates. This combination of characteristics delivers an exceptionally broad torque curve and more than enough horsepower to embarrass the same people who snickered at the idea of installing a 5.3-liter "truck" engine in a C4.
Before we could start the engine, the PCM had to be reprogrammed to accommodate a number of the changes we had made. In addition to replacing the original injectors with a set from an LS1 engine, we had also eliminated the mass air sensor and hadn't yet connected the oxygen sensors. The engine was also connected to a manual five-speed transmission (a TKO 600 from Classic Chevy 5-Speeds) instead of the original 4L60E automatic.
Obviously, life is now a lot...
Obviously, life is now a lot different for the PCM that controlled our 5.3-liter engine when it was originally installed in a Silverado. We used EFILive's V2 FlashScan cable and software, and a bench programming harness to flash a baseline tune in the PCM so we could start the engine. Subsequently, we used Flashscan's integrated scan and tuning capability to refine the original calibration.
Apparently, the Lord of Semiconductor Technology (LOST to those of us who deal with him on a regular basis) wasn't happy with me because the original calibration with which I reflashed the PCM would allow the engine to fire, upon which it immediately died. After checking and rechecking and finding no apparent cause for the problem, I fired up the EFILive tuning program again, built another calibration using a different operating system, and reflashed the computer once again. That must have brought a smile to LOST's face because the first time we hit the key, the engine started and ran perfectly.
One of the many advantages of EFILive software is the vast array of tables to which it provides easy access. When working with an engine conversion, access to those tables is particularly important because so many aspects of engine control are significantly different than they were in the original installation. (EFILive also includes a number of custom operating systems that include features ideally suited to engine conversions.)
If you attempt a C4orce-type conversion, keep in mind that in addition to all the standard considerations, the PCM calibration must be properly configured if alterations (from the configuration for which the PCM was originally programmed) are made in:
>>Air measurement type (from mass air to speed density) >>Injector flow rate (a change in injector size necessitates changes in the injector flow rate table)>>Fuel system type (return to returnless or vice versa)>>Oxygen sensor installation (if the sensors are eliminated, the PCM must be set to operate in open loop) >>Transmission type (changing from manual to automatic or vice versa)>>Rear axle ratio and tire diameter>>Desired idle speed>>Catalytic converter installation
Used LS1 intake manifolds...
Used LS1 intake manifolds are reasonably priced, and if you take advantage of that, you'll need LS1-style injectors. The original truck injectors are too short and have a different style connector.
If you plan to install an...
If you plan to install an LS2-style engine or intake manifold, you'll either need LS2-style injectors (which are shorter and have an EV6, rather than an EV1-style connector) or fuel rail spacers and EV1 connectors that will allow the use of LS1-style injectors.
We used a mounting bracket...
We used a mounting bracket from VettAid, made just for the purpose, to mount the PCM in the engine compartment. Once the PCM was mounted, a VettAid custom harness made wiring a plug-and-play proposition.
Most of these calibration changes cannot be made with a typical handheld reprogrammer, so you'll either need to obtain the required scanning and tuning software, or find an experienced tuner who can build an appropriate calibration and reflash your PCM. Another option is to use a stand-alone aftermarket ECM, but that's considerably more expensive than working with an original equipment PCM, which likely was supplied with the engine.
Whether you plan to use the injectors that were already with the engine or buy another set, it's a good idea to have them flow tested. Unless an injector is brand-new and in its original packaging (and sometimes not even then), you never really know the amount of fuel an injector flows. I've had brand-new injectors that didn't flow anywhere near their rated capacity, and I've had nasty-looking used injectors that were spot on.
Even though we knew the complete history of the LS1 injectors we used, we sent them to Chuck Leeper of Cody Motorsports to clean and test. The injectors had been removed from their original home about two years ago, and even though they had been sealed in a plastic bag and stored in an air-conditioned and heated shop, there was a good chance that evaporated fuel or the always-dreaded foreign matter would negatively affect at least one injector. According to Chuck, the most common problems with used injectors are leaks and poor spray pattern. Electrical problems (internal short or open circuit) are another possibility, although they are relatively rare.
The injectors in this set checked out on-the-money, and that minimized drivability issues. Using a milk crate for a driver's seat (literally, as many people who were at Carlisle can attest), attempting to alter the VE curve for anything other than idle conditions was neither practical nor prudent (although we've rarely let the latter consideration interfere with our plans). But since we knew actual injector flow rate, we didn't have to alter the original VE table very much to achieve good drivability. The only changes required were to accommodate the camshaft characteristics at and just off idle. Had rated and actual injector flow capacities not been spot on, VE table alterations would have been a protracted trial-and-error affair, with error being the operative term.
Following Carlisle, we hauled Project C4orce off to Mid America Motorworks, where it was on display and the subject of a seminar at the company's Funfest event. Prior to Funfest, we sent the car to Performance Choice, Mid America's manufacturing division, where Steve Wiedman and his crew designed and installed new upholstery and gave the rest of the interior some much-needed attention. Steve came up with a clean distinctive design that you'll be able to see in a future issue.