L46 350-HP 350 The starting point for the L46 four our test was the '70 LT-1 350 we built for September's story. Like the 327, the two 350 motors shared the 11.0:1 static compression ratio and big-valve fuelie heads, but the transition from LT-1 to L46 was a bit more elaborate than the previous 327 makeover. Naturally the LT-1 solid-lifter cam (different than the Duntov grind) was replaced with the L46 version (itself different than the L79 grind), but changes were also made to the induction system. Off came the aluminum dual-plane, high-rise intake and Holley carb and on went a cast-iron, low-rise dual-plane intake (casting number 184) designed to accept a Rochester Quadrajet carburetor.
Sean Murphy Inductions set us up with a Quadrajet that performed perfectly for our needs. The SMI Quadrajet was used on both the L46 and L82 combinations, though in reality the two motors utilized slightly different versions of the Q-Jet carburetor. Given the smaller primaries and massive secondaries, the Q-jet would likely offer a better combination of mileage and performance compared to the small Holley used on the L79. Like the 327, the 350 was reconfigured with factory-length 5.7-inch forged connecting rods (from Pro Comp) which offered no change whatsoever to the power curve, but we hated defending the use of 6.0-inch rods to the various forum members.
Like the 327, the new GMPP L46 cam was given plenty of break-in time prior to running along with a new container of high-zinc break-in lubricant from Lucas Oil. Keeping the engine speed above 2,000 rpm for 30 minutes is the best way to break in a new flat-tappet cam. We have had excellent results by combining the moly-based assembly lube, high-zinc break-in additive and a strict break-in procedure. The flat-tappet cams survive the break-in procedure and live a long, happy life it they are brought into the world properly.
After the break in, we dialed in the timing and SMI Quadrajet carb using some supplied metering rods. Naturally we wanted to test the three small-blocks with optimized air/fuel and timing rather than their factory settings. After dialing in the L46 combination, we were rewarded with peak numbers of 351 hp and 393 lb-ft of torque. Compared to the smaller L79 327, the L46 350 offered an additional 6 hp and 13 lb-ft of torque, not surprising given the increase in displacement. Basically the 350hp 350 offered more power everywhere compared to the smaller 327, with significant torque gains offered below 4,000 rpm. Torque production exceeded 375 lb-ft from 3,000 rpm to 4,700 rpm, making for one sweet torque curve.
L82 250HP 350 Though not revered quite like the L79s and LT-1s of the performance world, production of the L82 actually outlasted all of the other performance combos. Unlike the typical 3 to 4 year life span of the others (the L46 lasted only two years), the L82 was produced from '73 through 1980. Sure, the power output dipped from 250 hp through the mid-'70s to a low of just 205 net hp, but GM was able to revive the power output back up to 230 hp in the final year of L82 production. In a quest to drop the curb weight and improve the all-important CAFE (mileage) rating, GM even replaced the hefty cast-iron intake manifold in 1978 used on all previous L82s with an aluminum version of the Q-Jet intake. Since we were testing an early 250hp version of the L82, we decided it would sport the period-correct (771) cast-iron Q-Jet intake and SMI carburetor.