We've been refurbishing and...
We've been refurbishing and modifying Project C3 Triple-Ex for some time now, making the upgrades necessary for the installation of an engine with far more muscle than the current 350 is providing. This month, we'll outline our plans to repower this '71 Stingray.
As a Corvette owner, you're likely a bit of an adrenaline junkie, with a taste for carving the occasional corner or accelerating down a long Interstate on-ramp with your foot firmly to the floorboard. And while most Corvette engines provide plenty of power for an exciting ride, the initial excitement inevitably wears off, leaving you hungry for even more power. Fortunately, extra power is available from a variety of sources, and in many cases it can simply be bolted onto the current engine. In cases like ours, however, where extreme performance is desired, the existing engine simply won't suffice, and a build from scratch is the only choice.
While the options are nearly endless when it comes to engine builds for your Corvette, we narrowed our choices down to three: a traditional Chevrolet small-block, a Chevy big-block, or a late-model-LS conversion. Although the technological advances incorporated in the LS engine made it a tempting choice, and the guttural rumble of a big-block between the fenders does exude performance, we found an interesting compromise in a challenge posed by Editor Heath: Build a first-generation small-block to similar standards as the 7.0L LS7, and see if you can make more power.
Like many Corvettes, especially...
Like many Corvettes, especially C3s, our Stingray came equipped with a 350ci V-8. Since the engine in our car isn't original, we have no incentive to keep it, so all we had to do was decide whether to swap in a big-block, an LS, or stay with a small-block.
Since more power was the goal of this build, and because we've never backed down from a challenge, we decided that this approach not only fit the theme of our project car, but would make for an interesting comparison as well. And while it would be technically impossible to build a first-generation SBC to the exact standards of the 505hp LS7, we could certainly come close by using an aftermarket aluminum block and cylinder heads, and bumping displacement to an identical 427 ci. This engine swap would also be a comparatively simple affair, since Project C3 Triple-Ex is already equipped with a traditional small-block, and wouldn't require the wiring harness, ECU, and header changes an LS installation would necessitate. Even better, the large displacement SBC should give us a throaty rumble similar to that of a big-block Chevy-and we can even place a pair of 427 emblems on the hood.
With our goal in mind, we began looking for suitable parts to accomplish this engine build. Let's face it: With 505 horses and 470 lb-ft of torque, the LS7 is no slouch, so we'll need to do our homework to equal or surpass those numbers on pump gas. The LS7 comes from GM with an aluminum block, CNC-ported aluminum heads, a roller camshaft with nearly 0.600-inch lift, an arguably more efficient firing order, and 11:1 compression, so we felt all of these features were fair game when building our own small-block. And while we won't be using titanium valves like the LS7 engine, we will be using high-quality stainless-steel pieces, albeit in a smaller diameter.
We've spent a lot of time...
We've spent a lot of time modifying our C3 project car, with all new suspension, brakes, interior, instrumentation, and a Tremec TKO five-speed transmission. Now it's time for the payoff: a powerful new engine.
Hoping to duplicate the LS7 not only in terms of displacement but also in weight, we went to Dart Machinery for one of the company's aluminum SBC race blocks, a pair of PRO1 CNC-ported aluminum cylinder heads, and a matching single-plane aluminum intake manifold. Since the Dart block is available with a raised camshaft and wider, Oldsmobile Rocket-style oil-pan rails, it will easily accommodate displacements much larger than our planned 427 cubes. While the block is available in multiple deck heights, we ordered ours with a 9.025-inch deck and cylinders rough-bored to the same 4.125-inch diameter as the LS7. We also specified 50mm cam journals to facilitate the use of roller cam bearings. We like the 50mm bearings not because the roller configuration reduces friction (the difference is likely negligible), but because the larger-diameter 50mm core can help control cam flex and maintain truer valvetrain geometry at high rpm. Another nice feature of the Dart block is the wider pan rail, which makes it easier to install stroker crankshafts without the need to hand-clearance the block.
Dart's PRO1 CNC-ported aluminum cylinder heads incorporate 2.08-inch intake and 1.60-inch exhaust valves, along with 227cc intake runners. These heads offer enough flow to make great top-end power without sacrificing too much low-end torque, so they should be a good match for our 427ci engine. A Comp Cams solid roller camshaft with just over 0.600 lift will also be utilized; it will be ground to the LS firing order to more closely compare the two engines (and because we feel there's a slight advantage to the newer approach).
Now before you cry foul over the solid roller cam (the LS utilizes a hydraulic roller), remember that our small-block is giving up significant intake-valve size to the LS engine, and needs to compensate for that deficit somehow. Additionally, there's a common misconception among enthusiasts that a solid-lifter cam needs constant adjustment, is excessively noisy, and isn't especially streetable, all of which are untrue. By choosing the proper lobe design, a solid roller cam has indefinite life, requiring only occasional valve-lash inspections just like a hydraulic roller. And while valvespring wear may be slightly accelerated over a hydraulic roller, we feel the improved horsepower, torque, and throttle response will be well worth it.