C3 Corvette Engine Build - Welcome To The Machine (Shop)

Building A Small-Block Chevy To Out-Power The LS7

Dave Young Feb 28, 2011 0 Comment(s)
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For a VETTE Magazine project car to be true to the name, it has to perform-and no piece of the puzzle is more critical to performance than the powerplant. If you've been following our project, then you know that we've been modifying every aspect of Project C3 Triple-Ex, from the steering and suspension to the brakes and transmission. More recently, we upgraded the interior with replacement panels, race-inspired seating, four-point harnesses, and full Auto Meter instrumentation. Now that the car is finally ready, the culmination of our project is to build an appropriate engine.

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Last month we told you of our plans, brought on in part by Editor Heath's challenge to build a first-generation small-block Chevy engine that could out-power the formidable late-model LS7. While the LS engine does have some design advantages over the old small-block, the SBC is backed by a wealth of racing technology developed over the past 50-odd years. We're confident that these tips and tricks will enable us to exceed the LS7s power rating with a small-block of identical 427ci displacement.

While the temptation of an LS swap was certainly attractive, building an SBC for our project vehicle proved the better option for several reasons. Since our '71 is already equipped with a warmed-over 350, installing an architecturally similar engine will be simpler than adapting the engine bay for a late-model replacement. The expenses will be lower as well, as we won't need custom motor mounts, headers, or flywheel and bellhousing adapters to make the engine fit. Additionally, far fewer fuel-system modifications will be required for a carbureted small-block, as compared with a fuel-injected LS powerplant. With these factors in mind, we laid out a plan for our engine.

In last month's issue we highlighted the parts we'll be using for this build, including a Dart aluminum block, Dart Pro1 CNC cylinder heads, and a lightweight forged rotating assembly utilizing parts from Mahle and Summit Racing Equipment. We'll be duplicating the LS7 in terms of both bore and stroke, for an identical displacement. And thanks to its all-aluminum construction, our SBC should weigh roughly the same as well. But to actually out-power the LS7, we'll need to employ some engine-building tricks, many of which will be accomplished during the machining phase of the build.

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This month we'll visit our local machine shop, Auto Performance Engines in Auburndale, Florida, and follow along as owner Kevin Willis and his staff perform the necessary operations. The machining process isn't fully understood by many enthusiasts, but this phase is critical to an engine's durability as well as its output. Inaccurate machine work can lead to disappointing power numbers, as rings have trouble sealing to cylinders that aren't perfectly round and true. In fact there are a number of machining operations that can make or break an engine, and we'll show you all of them in this article.

We often hear that one machine shop charges significantly more than another for "the same work." But while the operations performed might be the same, the quality of the work isn't. It takes time to perform machine work accurately and correctly, and tooling must be replaced regularly to maintain this standard of accuracy. If we compare two identical engines-one with poorly performed machine work, and the other with accurately performed work-they may make similar power initially. After some street use or a few trips to the track, however, the "budget" engine will often make itself apparent by running slower lap or elapsed times, making less power on a dynamometer, burning oil, or, worse yet, scattering its internals through the oil pan or block.

You may be asking yourself why all this machine work is necessary if we're using new parts. We'll show you. While this engine can basically be bolted together, the cylinders need to be honed to their final size based on the diameter of the piston. We'll first measure the pistons, then hone the cylinders for precise piston-to-cylinder clearance. Also, because the Dart aluminum block is customarily used with dry-sump oiling, we'll need to machine some drain holes, so the oil can find its way back to the pan. For maximum quench area in the combustion chamber, we'll mill the deck of the block so that the piston is truly at the top of the cylinder at top dead center. We'll also cut deeper valve pockets in our Mahle forged pistons, then angle-mill the Dart heads. This will allow us to achieve a compression ratio of just over 11:1 with plenty of piston-to-valve clearance-even if we use our Jesel beltdrive to advance or retard camshaft timing.

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Knowing how critical the machining process is, and the complicated nature of what we wanted to achieve, we elected to use what we believe to be the best high-performance machine shop in central Florida, Auto Performance Engines. While the shop is not the least expensive in our area, owner Kevin Willis knows his stuff, replaces tooling regularly, and isn't scared to tell us if something isn't correct. Follow along now as APE performs the necessary steps to get our engine pieces ready for final assembly. And be sure to tune in to a future issue, as we put our LS7-killer small-block together, bolt it to the dyno, and see if we've achieved our goal of exceeding the LS7's 505hp rating.

Sources

Comp Cams
Memphis, TN 38118
800-999-0853
http://www.compcams.com
Auto Performance Engines
Auburndale, FL 33823
863-967-8781
Dart Machinery
Troy, MI 48084
248-362-1188
www.dartheads.com
Jesel
Lakewood, NJ 08701
732-901-1800
www.jesel.com
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