Engine Swap - Easy Big Block Swap
Photography by John Kiewicz
As corny as the old adage is, in most instances it's true: There's no replacement for displacement. And these days, with the availability of stout mail-order crate engines, the cost of buying a brutish big-block is now within the budget of many gearheads.
Case in point: GM Performance Parts' burly 502/502 big-block (PN 12371171) that can be had for about $6,000. In the Sept. '97 "Crate Engine Shootout!" story we tested the 502/502 and were giddy to see 513 hp and 555.5 lb-ft of torque. However, even though a crate engine's price may be lower than what you'd spend building a similarly performing mill, we wondered what hassle and expense would be required to shoehorn such a fat-block into a traditional musclecar.
We'd always heard that a big-block Chevy was an easy swap into a small-block car--but is it true? With the 502 and an A-body on hand, we decided to find out for ourselves and share with you the details and the costs. As usual, CC's much-abused Cheap Street Chevelle was the guinea pig, but much of the info will apply to most '68-'72 GM A-bodies or GM fullsize barges.
After jerking the small-block and test-fitting the 502, the first thing we learned was that the 502/502 comes with a six-quart truck-style oil pan that interferes with the engine bay in our '70 Chevelle. We replaced it with a special Milodon oil pan that merges the correct old-car-shape to fit the chassis with the new-car-type pan rails that fit the new Gen 5/Gen 6 big-blocks and their one-piece rear-main seals and revised gaskets. The Milodon oil pan's unique design has a large seven-quart oil capacity for reliable oiling during racing yet is a low-profile design to avoid ground-scraping woes. Often, you can reuse the 502's stock one-piece rubber oil pan gasket, but if not, companies such as Fel-Pro offer a gasket under PN OS34407R.
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The Milodon oil pan (PN 30955) requires a special oil pick-up tube assembly (PN 18301) to
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If your '68-'72 GM A-body originally came with a 350 small-block, you can retain the origi
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We installed a new Milodon 160-degree-F thermostat and then bolted on a reproduction big-b
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The 502/502 comes with an aluminum water pump, but it's designed for Reverse rotation and
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New crank and water pump pulleys are available from OPG. We opted for LS6/L78-style deep-g
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The small-block alternator brackets won't work with the big-block, so we installed OPG's b
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We found out the hard way that small- and big-block (right) power-steering pumps looked th
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A big-block (including Gen 5/Gen 6 big-blocks) fits into the engine bay of a GM A-body wit
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We learned that the passenger-side header must be installed from underneath the car. Have
By John Kiewicz
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