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. The Milodon oil pan (PN 30955) requires a special oil pick-up tube assembly (PN 18301) to be properly oriented within the new oil pan's sump area.The Milodon oil pan (PN 30955) requires a special oil pick-up tube assembly (PN 18301) to If your '68-'72 GM A-body originally came with a 350 small-block, you can retain the original engine frame mounts. If it had a 307 V-8, you'll need to switch to 350/396/454-style engine frame mounts (GM PN 3980711 left, 3980712 right), which should also work on non-Chevy A-bodies. On the engine side you'll need to upgrade to new GM big-block engine motor mounts (PN 03962748).If your '68-'72 GM A-body originally came with a 350 small-block, you can retain the origi We installed a new Milodon 160-degree-F thermostat and then bolted on a reproduction big-block-style thermostat housing (PN 26016) from OPG. Rather than reusing the crusty old bolts from our small-block, we opted for an ARP big-block bolt kit (PN 535-9501).We installed a new Milodon 160-degree-F thermostat and then bolted on a reproduction big-b The 502/502 comes with an aluminum water pump, but it's designed for Reverse rotation and would require switching to modern-style serpentine belt-type pulleys and brackets that would be a bit pricey. We installed a new Edelbrock long-style aluminum water pump (PN 8851) that accepts traditional early type pulleys, brackets, and hoses.The 502/502 comes with an aluminum water pump, but it's designed for Reverse rotation and New crank and water pump pulleys are available from OPG. We opted for LS6/L78-style deep-groove crank (PN SL39119) and water pump (PN SL39414) pulleys to avoid any high rpm belt-throwing mishaps. A 15450 fan belt fit perfectly.New crank and water pump pulleys are available from OPG. We opted for LS6/L78-style deep-g The small-block alternator brackets won't work with the big-block, so we installed OPG's big-block alternator bracket set (PN FL8502). Our old alternator already had an aftermarket deep-groove aluminum pulley, but if you want one of OPG's deep-groove pulleys, order PN SL39120.The small-block alternator brackets won't work with the big-block, so we installed OPG's b We found out the hard way that small- and big-block (right) power-steering pumps looked the same, but had slightly different lines exiting the back. To use OPG's factory-type big-block brackets (PN SFL8504) we also needed to upgrade to a new (expensive, ouch!) big-block power-steering pump (PN TRI6165) from OPG.We found out the hard way that small- and big-block (right) power-steering pumps looked th A big-block (including Gen 5/Gen 6 big-blocks) fits into the engine bay of a GM A-body without much hassle, but getting headers to fit was the real trick. Hedman offers two varieties of 13/4-inch headers (full length and 3/4-length) that work great. We opted for Hedman's 3/4-length headers (PN 68610) because they're easier to install, tuck up tighter, and provide added ground clearance. The headers can also be ordered with a trick hi-temp coating for an added price, but gaskets and bolts were included free. Before installing the engine, we test fit the headers to make sure they cleared the gear-reduction starter (included with the 502), motor mounts, and oil pan. If you prefer, stock-type manifolds are available from OPG.A big-block (including Gen 5/Gen 6 big-blocks) fits into the engine bay of a GM A-body wit We learned that the passenger-side header must be installed from underneath the car. Have one guy slip the headers in from below while another installs the gasket and bolts (included) from above.We learned that the passenger-side header must be installed from underneath the car. Have Installing the driver-side header was even trickier. After numerous failed attempts we realized that you must remove the driver-side motor mount bolt, slightly lift up on the engine with the hoist, slip the header in from below, lower the engine, and then install the gasket and bolts.Installing the driver-side header was even trickier. After numerous failed attempts we rea Once the engine is bolted to the motor mounts and the headers are in place, bolt the tranny to the back of the block. Then, from under the car, bolt the big-block's flexplate to the torque converter. Both the bellhousing and the flexplate use the same bolt pattern as the small-block, so that's no big deal. If you're running a manual tranny, you'll need to swap the 502's stock 12-inch flexplate for GM's 14-inch flywheel (PN 14096987).Once the engine is bolted to the motor mounts and the headers are in place, bolt the trann The 502/502 comes with a specially calibrated HEI distributor. To avoid breakage, we removed the distributor during engine installation and reinstalled it once the engine was in place. Afterward, we installed the heavy-duty 8mm spark plug wires included with the 502 crate engine.The 502/502 comes with a specially calibrated HEI distributor. To avoid breakage, we remov To retain original heater hose routing, we used OPG's big-block water pump nipple kit (PN WP21551) with heater hose nipples that thread into the intake manifold and water pump (arrows).To retain original heater hose routing, we used OPG's big-block water pump nipple kit (PN Big-block-equipped GM A-bodies used a slightly different (actually smaller) radiator fan shroud than small-block cars. To maintain proper fit and cooling, we installed OPG's reproduction big-block fan shroud (PN PZ01017).Big-block-equipped GM A-bodies used a slightly different (actually smaller) radiator fan s Small- and big-block clutch fan assemblies differ in size and strength. Our stock small-block clutch measured 6x21/4 inches, while the new OPG big-block clutch (PN FC57) measured a larger 71/4 x21/2-inches. The stock fan, however, interchanges small- to big-block.Small- and big-block clutch fan assemblies differ in size and strength. Our stock small-bl Rather than use universal flex-type radiator hoses, we installed new LS6/L78-type lower (PN 3959188) and upper (PN 3942453) molded radiator hoses. We cut off 1 inch of hose on the thermostat housing side of the upper hose for an improved fit.Rather than use universal flex-type radiator hoses, we installed new LS6/L78-type lower (P The new Holley carb didn't like the Q-jet linkage brackets from our small-block, so we procured the proper Holley carb throttle bracket (PN KM02019) from OPG.The new Holley carb didn't like the Q-jet linkage brackets from our small-block, so we pro After the 502 was running, we needed to fab some pipework (arrow) to connect the Hedman headers to our existing Borla 3-inch exhaust. After illegally cruising open-headered to Borla and dishing out some serious schmoozing, Borla fabbed up the needed pipework.After the 502 was running, we needed to fab some pipework (arrow) to connect the Hedman he We went to a local speed shop to buy a new Holley carb inlet fuel line (PN 34-160) only to find out that it was the wrong unit (arrow). Actually, we needed PN 34-150 to properly fit the dual-metering-block 850-cfm vacuum secondary Holley carb fitted to the 502/502. After scouring an auto parts store, we came up with a PCV valve that had a 90-degree bend (Auto Tune PN PT3771) making for a sano installation of our PCV breather system that tapped into the back of the Holley carb.We went to a local speed shop to buy a new Holley carb inlet fuel line (PN 34-160) only to We filled the 502 big-block with fresh oil and coolant, rough-timed it, then cranked it over to bring it to life (the engine had been dyno tested and was already broken in). With the distributor vacuum advance disconnected, the initial timing was set to 12 degrees BTDC with a total advance of 36 degrees, then the carb floats and air idle bleeds were adjusted. Because the 502 was taller than the 355, we had to switch to a drop-base-type K&N air filter assembly (arrow) for hood clearance.We filled the 502 big-block with fresh oil and coolant, rough-timed it, then cranked it ov With its all-steel bodywork, six-point rollbar, 4L80E overdrive tranny, and a half-tank of fuel, our Chevelle (without driver) weighed in at 3,710 pounds with the 355 small-block. In the same condition, but with the aluminum-headed 502 big-block in place, our Chevelle's weight swelled to a porky 3,840 pounds and the nose dropped down about 1/2-inch.With its all-steel bodywork, six-point rollbar, 4L80E overdrive tranny, and a half-tank of We wheeled the car to the high desert merriment of L.A. County Raceway for some drag test action. Speaking of a drag, for our earlier cross-country roadtrip we replaced our drag-friendly 3,000-rpm stall converter with a cruise-friendly 1,400-rpm converter that killed us off the starting line. Regardless, with pump gas, full exhaust, and wearing a pair of Mickey Thompson E.T. Street 26x10.5-15 tires, the 502-equipped Chevelle hustled to a 12.41 at 111.41 mph. With a performance converter it would run 11s, dammit!We wheeled the car to the high desert merriment of L.A. County Raceway for some drag test SOURCES Edelbrock Dept. 5.0 2700 California St. Torrance CA 90503 310-781-2222 www.edelbrock.com Milodon Inc. 20716 Plummer St. Chatsworth CA 91311 818-407-1211 GM Performance Parts www.gmperformanceparts.com Original Parts Group (800) 243- Hedman Hedders 16410 Manning Way Cerritos CA 90701 310-921-0404 www.hedman.com Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!