396ci Chevrolet Chevelle Engine Rebuild - Freshening Up A 396ci Chevelle

Rebuilding a Mild 396 for More Power

Jeff Smith Sep 1, 2003 0 Comment(s)

Not long ago, in a land infested with high-compression musclecars and four-speed bruisers, the 396ci Chevelle was a respected performance car even when predators like 428SCJ Mustangs and Boss 429s prowled the boulevards looking for prey. The little 396 could hold its ground against the more nimble small-block cars and could certainly beat up on many 383 Mopars and 390 GT Fords. The 396 wasn't a heavyweight like an LS6 454, but it enjoyed a respected performance legacy.

The '66 SS 396 Chevelle was the first full-production-run Chevelle to get the 396. There had been 201 Z-16 Chevelles built in 1965, which became the prototypes for the following year. The '66 396s came in three versions: the Q-jet-topped 325hp version, the 600-cfm Holley-fed 360hp version with oval-port heads and a hydraulic cam, and the more radical 375hp 396 with a mechanical cam and rectangular-port heads.

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Back in the day, everybody wanted the 375hp version. When the author bought his '66 Chevelle in 1971, it came with the 360hp version with the "lo-po" oval-port heads. Now fast-forward to rebuild time for this aging musclecar. The engine suffered through an early rebuild and made a disappointing 342 hp on the dyno at 5,000 rpm complete with oversized 17/8-inch headers and a single-plane intake back in the mid-'80s. We decided to freshen it up and rebuild it close to an original 360hp engine with a few refinements.

The steel-crank bottom end was virtually new, using forged pistons, but it had been built in 1980 when the only people using torque plates for honing were Pro Stock racers. We figured we could improve the ring seal with a "round" cylinder wall prep, so we pulled the engine completely apart. This was good because the bearings were less than perfect, although the crank survived unscathed. After taking >> the block to Jim Grubbs Motorsports in Valencia, California, our concerns were justified when owner Jim Grubbs reported significant shadows on the cylinders after the first honing pass with the torque plates installed, which indicated that the bores were anything but round with the heads bolted on. For the freshen-up, we used new Federal-Mogul rings and bearings, but we had to resort to using a second set of +1 performance bearings to mix with the standard rod and main bearings to establish the proper bearing clearances. The original 396 oil pan had seen better days, so we replaced it with a Milodon pan, oil pump, and windage tray to update the lubrication system. Combined with a one-piece oil-pan gasket from Fel-Pro and a Milodon timing chain cover, we had the bottom end dialed in with little difficulty.

Next came time for the cam selection. Since this engine was destined for mostly Saturday-afternoon cruising duties with an occasional blast down the 1,320, we wanted power, but also something similar to the original factory 360hp hydraulic-lifter cam. After a little research we came upon the Crane PowerMax 272 cam, which offered very similar timing numbers at 0.050-inch tappet lift. The Crane was within 2 degrees of the factory cam at 0.050-inch tappet lift on the intake but offers 10 degrees more exhaust duration. That all sounded good, so the Crane got the chance to prove its mettle.

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Next on our priority list came the heads. Conventional wisdom has shown us that oval-port heads are the right choice for a 454. If anything, our 260cc oval ports are perhaps a little big for a small 396 Rat, but that's what the factory bolted on, so we intended to make the most of these castings. We employed new stainless steel valves from Federal-Mogul and then hit the area directly underneath the valve seats with a die grinder doing a quick, two-hour pocket-porting job. We removed what was necessary to improve the radius into (or out of) the combustion chamber, but we didn't try to unshroud the valves by moving the chamber walls back. The final modification was to include a set of Viton rubber positive valveguide seals to ensure very little oil would enter the chambers.

Once the long-block was reassembled, we also added a set of Crane hardened pushrods and a set of 1.7 roller rockers because we remembered having to constantly battle rocker-arm problems with the original Rat. Topping off the valvetrain was a slick set of PML cast-aluminum Chevrolet-script valve covers that gave our 30-something Rat a contemporary look with a hint of nostalgia. Since we were looking to maintain the general appearance of our 396, we also decided on an Edelbrock Performer dual-plane rather than a Performer RPM, which is much taller with more power potential. The original 360hp intake was a cast-iron monster that belongs in a museum and not on the car, so we elected to go with the Performer.

We cheated in a way with the dyno test, since we went with an HEI distributor much larger than the original points-type distributor, to which we added a set of universal MSD plug wires. We will probably change this to a Pertronix or other conversion to maintain the original image.

Of course, we couldn't just run cast-iron manifolds on this engine, so it had to have a set of Hedman headers. Combined with a Flowmaster exhaust system complete with the larger Big Block II mufflers, this will make this combination quiet yet powerful.

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