Subscribe to the Free

Chevrolet Engine Swap Parts - Rat-ify Your Chevrolet

Mouse to Rat—What You Need

Bob Mehlhoff Sep 1, 2001

Step By Step

Installing a big-block properly requires the correct frame brackets. The two in this photo are from a ’66 Chevelle SS 396. These brackets mounted the big-block engine slightly lower than its small-block counterparts. Although small-block mounts will work, they will not position the engine properly. These big-block brackets are simply bolted to the frame and attach to the motor mounts. Although an original set may be hard to find, reproduction pieces are available from Classic Industries, Original Parts Group, and Year One. Remember too that big-blocks weigh more than small-blocks. Think about upgrading the front coil springs and sway bar to handle the extra weight.

If you’re looking for big-block headers, the pipe spacing can identify them. Notice that the big-block header (shown upper) has evenly spaced tubes. Small-block headers (shown lower) join the two center tubes. Remember that headers are not only designed for the engine, but also for the chassis. So be careful buying used headers.

Early big-block alternators (’68 and earlier) used this set of brackets and were used with a short-style water pump. These mounted on the left (driver side) of the engine. The cast piece bolted to the cylinder head, and the stamped piece was attached to the intake manifold and water pump. These are either available from reproduction sources or as chrome dress-up items from aftermarket sources.

The early small-block pieces (’68 and earlier) are shown here for comparison. The lower piece bolted to the driver-side exhaust manifold. These will only work with small-block engines.

Beginning in 1969, all passenger-car V-8s went to a long-water-pump design. The alternator location also switched to the right (passenger side) and used newly designed upper and lower mounting brackets. This photo shows ’69 to mid-’70s big-block brackets.

This photo shows ’69 to mid-’70s small-block brackets. Remember that many of these pieces were not only designed for small- or big-block engines, but also for the body style. This is especially true for power-steering brackets. Notice the difference in reach the big-block’s upper alternator bracket (one photo up) has to attach to the thermostat-housing stud compared to the small-block’s upper alternator bracket (this photo).

Big-block lower crank pulleys can be identified by the larger center hole (left) compared to the small-block piece (right). Be certain to get pulleys that match your water-pump length and belt requirements.

If you’re sorting through a stack of Chevrolet pulleys, the big-block pulley’s center hole measures 2 inches.

When shopping for pulleys, be certain to verify the size and count of pulley grooves needed. If possible, it’s best to buy pulleys as a set for your application.

Since big-blocks generally produce more heat and are larger displacement engines, they require better cooling systems. A stock small-block two-row radiator (shown right) may get you by if you live in Northern Canada, but if summer temperatures get over 85-degrees F, think about adding a three- or four-row (shown center and left respectively). Be certain to select a radiator that fits your core support. Cars that use an upper and lower panel to retain the radiator are the friendliest to cross fit. Don’t forget to add the correct fan and fan shroud, too. These are also available from many reproduction sources.

Torque and lots of cubic inches are what big-block–powered Chevys are famous for. Whether it’s a 396ci or Chevrolet’s latest 502ci crate engine, Rat motors are synonymous with power. During the ’60s and ’70s, Chevrolet’s porcupine (canted-valve) engine was available in a variety of musclecars. Although most Chevrolets came equipped with a small-block, installing a big-block can frequently be done with a minimum of hassle. Motor mounts, headers and exhaust, pulleys, and a larger radiator are just a few of the items you may need to install a Rat motor into your ride. But when you’re done, you’ll realize that there’s no replacement for displacement.


Connect With Us

Get Latest News and Articles. Newsletter Sign Up

sponsored links

subscribe to the magazine

get digital get print