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C3 Big-Block Engine Swap - Big-Block Party

Installing an injected Rat motor for improved performance, fuel mileage, and driveability

Paul Sisia Aug 1, 2011
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If you're reading this headline, especially the part about better fuel mileage, and shaking your head, you're not alone. Virtually everyone we spoke to said it just wasn't possible. More than one even advised against wasting our time. So the real question is, why would we even try?

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Well, like every owner of a small-block- powered C3 Corvette, we're just sick and tired of hearing the same annoying question. At every local car show it's, "Does it have a big-block?" At the cruise-in, "Does it have a big-block?" Heck, at just about every stoplight, "Nice Vette...does it have a big-block?"

Let's face it: big-block Corvettes are legendary, both on the street and on the track. They have the mystique, the power, and a sound that just can't be duplicated by a small-displacement powerplant. Plus, that look is unmistakable. If you want to instill a sense of awe when you open your hood, nothing beats those wide valve covers--and, if you're lucky, a triangle air cleaner sitting atop a trio of two-barrel Holley carbs, the automotive trifecta.

The Plan
Our aim is to show you how to remove your small-block and then build and install a big-block that looks virtually identical to the 427/435 engine we should have ordered back in 1969. Only this time, there will be no leaking carbs, no difficult cold and hot starts, no fouled spark plugs, and no 6 mpg like the original delivered. No, this will be a modern, aluminum-headed engine with a unique triple-throttle-body fuel-injection system--triangle air cleaner and all. It'll be mated to a super-duty Gearstar 4L60E transmission that can handle the power and help deliver both impressive fuel mileage and lower-rpm highway cruising.

The Vehicle
We'll be using a beautiful Daytona Yellow '69 convertible running a non-original 406ci small-block. It's a great motor, but it's inherently compromised by the previous owner's desire for top-end power and a good quarter-mile sprint time. It has a single-plane intake, a big-jet Holley four-barrel, and a dual-point ignition system without vacuum advance. That's all fine for top-end power but doesn't help with low-to-mid-range performance or driveability--and it's certainly not set up to deliver maximum fuel mileage.

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As a baseline, this engine was averaging only 10 mpg. Simply switching out the big Holley carb for a smaller unit improved fuel mileage 40 percent. That's a nice increase, but it's still hard to jump up and down about 14 mpg.

Our 406 also suffers from some troublesome oil leaks from the typical spots: valve covers, oil pan, rear main seal, and even around some of the intake-manifold bolts. We've put off pulling the motor, resealing it with new gaskets and replacing the carb, intake, and ignition because, well, we just couldn't stop dreaming about how great the car would be with a big-block. Let's stop dreaming and get started.

Removing the Engine and Transmission
We'll begin with a stern admonition: Do not attempt this job by yourself. There's no better way to injure yourself than to try to remove an engine and trans without assistance. Because of the weight and bulk of the parts involved, this operation requires a hoist and several sets of hands to guide them out without damaging your vehicle. That's especially true when your vehicle is made of fiberglass.

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If you're searching for a shop to do the work for you, the first thing to do is contact your local Corvette Clubs for recommendations. For this particular project, look for a shop that is experienced with older Vettes, and with big-blocks in particular. During our search, we were surprised to hear recommendations for the Jim Ellis Corvette Center, part of a large, family-owned Chevrolet franchise here in the Atlanta area. This particular dealership's lead tech, David Fulcher, is a Master Certified Corvette Technician. He built and autocrossed his own big-block C3 years ago. And when we asked, "How long have you worked on Corvettes?" his reply was a reassuring, "Every day for the past 30 years."

It's also quite comforting to drive your old Vette into a brand-new, 80,000-square-foot service facility with a huge Chevrolet sign on top and more Corvettes on the premises than you can count.

First Steps
Make it easy on yourself. Before trying to remove the engine and trans, take the time to remove all of the bolt-on items that get in the way. The air cleaner, carburetor, distributor, exhaust manifolds, A/C compressor, alternator, power-steering pump, cooling fan, and all the pulleys add weight to the engine. Remove the starter as well. And don't forget to drain the engine oil, the transmission fluid, and the coolant from both the radiator and the block. (There are small drain plugs on each side of the block for this purpose.)

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It only takes about two hours to remove all of the above items, and no special tools are required. A set of open-end wrenches, screwdrivers, and a socket set will do the trick.

While you're at it, take particular note that the radiator can easily be damaged. To avoid this, remove the top and bottom hoses, the two bolts that hold the top of the shroud to the core support, and the two nuts on the bottom of the shroud (one on each side). Finally, remove the shroud and lift the radiator straight up and out.

Before we got too far, Fulcher was quick to point out an item unique to Corvettes: the engine ground straps. They'll also need to be disconnected before trying to pull the engine.

Fortunately for us, the Jim Ellis Corvette Center had all the tools required to handle the heavy lifting, too. An engine hoist, a hydraulic transmission jack, and a pneumatic ratchet should make the removal a snap.

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With the engine and trans out of the way, it was time to make a quick assessment of any other areas that might need to be addressed. Big-block springs, some new upper and lower control-arm bushings, and a better cooling system were obvious, but we'd also need to make sure the rear differential could handle the tremendous twist generated by the new powerplant. But before we started on any of that, we sent the car to the paint-and-body shop to clean, prep, and paint the engine compartment.

Detailing the Engine Compartment
This Collision Center handles repair for all of the Jim Ellis dealerships, including Porsche, Audi, Saab, VW, GMC, Buick, Hyundai, and Mazda. Needless to say, it's a huge, state-of-the-art facility with new Porsche Panamera Turbos and GT3s, Audi R8s, ZR1 and Z06 Corvettes, and a sea of other cars in various stages of collision repair. After we met with the Center's director and outlined the project, we spoke with the body-shop manager who would personally manage the entire process. He took a written, detailed account of the work to be performed and scheduled the initial prep to be done on one of the Center's hydraulic lifts.

Having the car up in the air made it easy to reach all the tight areas of the engine compartment, the frame, and the underbody. While on the lift, the Center's techs pointed out a few small holes in the footwell and the trans tunnel, and scheduled a body man to do these repairs first. They also allowed us to remove the upper and lower control arms, the rear diff, the trailing arms, and anything else we wanted to send out to have repaired, painted, or powdercoated. Special care was taken to mask off the engine bay and to "bag" the whole car to avoid overspray.

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Next, the engine compartment and underside were thoroughly degreased, scuffed, and sanded. Finally, these parts were rinsed clean before satin black paint was applied for an as-new finish.

Odds and Ends
Although the heart of this project is the powertrain swap, there are an awful lot of ancillary parts that should be replaced or upgraded while the engine and trans are out of the car. Now is the time to inspect the shocks and springs, the brake pads and rotors, all the rubber bushings and hoses, and so on. Take a close look at each item and decide if you want to replace it with stock hardware or high-performance aftermarket items. Then, make a thorough list of these parts.

Once your list is complete, you can start hunting for parts. While you can literally spend days online looking at parts and prices, we decided to take a shortcut and call the guys at Summit Racing. They had everything we needed in stock, with guaranteed low prices and same-day shipping. It seemed as though every time we blinked, a fresh shipment of performance parts had showed up at our doorstep. It was like Christmas in July.

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For the Corvette restoration parts such as the big-block springs, the ball joints, the tie-rod ends, that sweet triangular air cleaner, and just about everything else that popped up during the removal process, we called the guys at Volunteer Vette. They speak Corvette fluently and had everything we needed, including a few items we didn't even know we needed.

What's Ahead
In our next installment, we'll begin our big-block buildup in earnest, starting with a custom- made, Tri-power fuel-injection system by F&B Throttle Bodies. We'll also meet legendary engine builders Lamar and Rob Walden, who will be testing our AFR aluminum oval-port heads on their flow bench, selecting our custom Comp camshaft, and assembling this cutting-edge powerplant. Don't miss it.


Gearstar Performance Transmissions
Akron, 44308
Air Flow Research
Valencia, CA 91355
Comp Cams
Memphis, TN 38118
Summit Racing
Akron, OH
F&B Performance Engine
Cardiff by the Sea, CA
Lamar Walden Automotive
Doraville, GA 30340
Volunteer Vette
Knoxville, TN 37914
Jim Ellis Chevrolet and Corvette Center
Atlanta, GA 30341



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