When it comes to the powerplant for any Corvette, we've always hewed to the theory that too much horsepower is a good thing. And while an abundance of torque and power can get an inexperienced driver into trouble, especially in a car without modern traction control, it gives the prudent wheelman the ability to modulate the accelerator pedal as conditions warrant, guaranteeing optimum performance in any situation.
Alternatively, it doesn't matter how hard the driver pushes the accelerator in an underpowered vehicle; once full throttle is reached, there's just nothing left. With these thoughts in mind, and having accepted a challenge from esteemed and handsome Editor Jay Heath, we ended up building a beast of a small-block Chevrolet engine for our Project C3 Triple-Ex.
The challenge was this: Build a first- generation SBC engine to roughly the same specs as the 505hp LS7, and outpower it running on 93-octane pump gas. At the outset we were skeptical that we could really duplicate the LS7 with off-the-shelf parts. But using a block and cylinder heads from Dart Machinery, with internals from Summit Racing Equipment, we built an all-aluminum small-block with the same bore and stroke as the LS7, netting very close to 427 cubes. We also kept compression pump-gas friendly at just over 11:1, much like the LS7 we were trying to duplicate.
To further mimic the LS7 we chose our Comp roller camshaft to make peak torque and horsepower at an rpm very close to the LS7's peak. This was tricky, but with the help of the Comp engineers, our engine achieved its peak of nearly 540 lb-ft of torque between 4,800 and 5,000 rpm, and maximum horsepower at 6,500 rpm.
Even better, we exceeded our goal without the use of exotic parts like 18-degree cylinder heads, which would have required us to fabricate expensive and time-consuming custom headers, among other drawbacks. We did use high-quality parts, including Jesel shaft-mounted roller rocker arms, and a Comp roller cam and lifters. Our rotating assembly consisted of lightweight Scat rods with a Scat forged crankshaft, along with Mahle forged pistons from Summit Racing Equipment to ensure the durability of this engine matched its power output.
If you've been following this project in previous issues of VETTE, you'll recall that we've already beefed up many of C3 Triple-Ex's systems to cope with our new, more powerful engine. This includes upgrades to the car's cooling and fuel systems, brakes, suspension, and instrumentation. We also installed a Tremec TKO five-speed transmission with a kit from American Powertrain, which we'll fortify during this swap with a new DFX clutch-and-flywheel kit from Centerforce. Having completed all this work on our Stingray, and with the engine fresh off the dyno, we were eager to place the motor between the framerails and enjoy our first drive.
Any time you change the engine in a car, there are certain items you should replace at the same time. Fortunately for us, our LS7-killer uses components of standard SBC dimensions, so no custom parts, such as headers or motor mounts, were needed. Our Jesel beltdrive did require a swap to the "long" small-block water pump, so we ordered a set of March aluminum pulleys from Summit Racing that would work with that configuration.
Additionally, our engine is quite a bit healthier than the 350 we're pulling out, requiring headers with larger primary tubes. Fortunately, Summit had the Hooker headers we needed in stock, and got them to us in only a few days. Our motor mounts and cooling system pieces are new, and we're also installing a new MSD high-torque starter.
Whenever you're performing an engine change, replace any questionable components, and also take the time to update life-limited items such as cooling, fuel, and ignition-system parts. Nothing is worse than frying a new motor with a clogged radiator, a bad thermostat, or a dead water pump. The engine-driven fuel pump and all filters should be changed at this time as well, ensuring an adequate supply of clean fuel to the new engine.
Though it may seem that an engine swap in any car would be cumbersome, these older Corvettes make the job less difficult than you might surmise. There's a surprising amount of room in the engine bay, and the car's systems are fewer and simpler than on newer models, making this a basic, nuts-and-bolts operation.
Because the five-speed transmission is a tight fit—and since changing an engine in any car with a quality paintjob demands extra care—we enlisted the professionals at Inline Performance Specialists in central Florida to lend us an extra set of hands. With the assistance of Tod and Garret Struck at Inline, we made short work of the operation, easily completing the swap over the course of a Saturday.
Making the job easier, of course, was the fact that we'd already tuned our LS7-killer on Auto Performance Engines' engine dyno. Nothing beats simply bolting an engine in place and turning the key to have it start and run properly from the get-go. (There's still something to be said for the basic approach of a quality carburetor and electronic ignition.) With our Stingray running, we only had to verify that ignition timing hadn't changed, then hook up our exhaust system. Unfortunately, due to the design of our car's exhaust and the new Hooker headers, we did need some new parts to make it work.
This month we'll show you the installation of our LS7-killer SBC, along with the parts necessary to ensure that Project C3 Triple-Ex stays operational for a long time. This is shaping up to be a seriously fun car, and an initial, open-header blast around the parking lot (OK, and maybe down a back road) revealed that our Vette now has power to spare. We've ordered an exhaust system, so it won't be long before we can drive the car on the street and take it to the track for testing. Be sure to follow our project in future issues of VETTE, and look for videos of our first drive on vetteweb.com.