My understanding is that there was no L48 in 1981. The L48 appeared in '73... and ended in 1980.
1973: The solid-lifter LT-1 is discontinued as factory-delivered performance levels continue to slip. Appearing in its place is the L48, a hydraulic-cammed, Quadrajet-carbed package that emphasizes low-end grunt rather than top-end power. Its 250 hp at 5,200 rpm contrasts with the previous LT-1’s 255 hp at 5,600 rpm. Torque increases (by 5 lb-ft) to 285 lb-ft. At the other end of the scale, the L65 350 is available in Chevelles and El Caminos with a two-barrel carburetor. It is the weakest 350 of all time, generating 145 hp at 4,000 rpm and 255 lb-ft at 2,400 rpm.
1974: Chevrolet substitutes lighter, thinner head castings on most production small-block applications in an attempt to reduce vehicle mass for improved fuel economy. These ’74-up heads are more prone to cracking, have less material left after radical porting, and should be avoided. This is the final year for big-block (454) Corvettes; afterwards it’s 350 all the way (overlooking a few sickly 305s).
1975: The best news for ’75 is the introduction of the HEI, coil-in-cap, large-diameter distributor. The Z28 is discontinued, single catalytic converters make the scene on most models and sap even more power before blowing through bogus twin tailpipes on Corvettes and 350 Camaros. The thickness of the rubber oil seal between the oil pan and timing chain cover is increased from ¼ inch to 3/8 inch on all small-blocks. To tell the difference, place a straight edge across the pan rails over the front gasket half-moon cutout and measure the distance from the seal surface to the bottom of the straightedge. If the distance is 2¼ inches, use the earlier ¼-inch thin seal. If the distance is 23/8 inches, use the 3/8-inch thick seal.
1976: The Corvette 350 gets a two-pronged shot in the arm: The base L48 adds 15 hp (to 180), and the optional L82 gains 5 hp (to 210). Despite the modest output, L82s still use a four-bolt block. The only 350 option offered in Camaro is the LM1 with a four-barrel and 165 hp; no four-bolt blocks here. Though the Nova SS is viewed by serious enthusiasts as a blasphemous charade, the little-known COPO 9C1 law enforcement option transforms Nova coupes and sedans into exceptional handlers. Even though the mandatory-option LM1 350 is only capable of 155 hp and 250 lb-ft, a cult hero is born.
1977: January 14, 1977, Chevrolet announces the return of the Camaro Z28 with a 170hp/280-lb-ft 350. A total of 14,347 are sold, the vast majority with automatic transmissions. Downsizing reshapes the fullsize Caprice/Impala (B-bodies) and sheds 600 pounds of flab. Motor Trend reports that with the optional LM1 350 (also rated at 170 hp) “it’s as quick as the older car equipped with the 400cid 4-bbl engine.”
1978: The Corvette celebrates its 25th anniversary with the Indy Pace Car Replica package (RPO Z78), adding $4,207 to the price tag. The “Indy package” ignites a market frenzy that results in cars trading for two and even three times the sticker price before the whole thing blows over. Peak power comes from the L82 350, now pushing 225hp. California buyers have to settle for the 195hp L48 350.
1979: In its second year after being downsized, the Malibu gets an optional 170hp 350. The catch is you have to be a cop to get one. The rest of the RPO 9C1 law-enforcement package can be ordered by civilians, but the 145hp L35 305 is as wild as it gets. The Camaro’s Z28 350 peaks out at 175 hp while Corvette pegs 225.
1980: L82 350 Corvette buyers mourn the loss of manual transmissions but get an extra 5 hp (to 230). You’ll have to order the 190hp L48 350 if you want to throw powershifts. Pity the Californians; they’re stuck with no choice but the ultra-tame, automatic-only, 180hp L64 305. The dipstick location shifts to the passenger side of the block. Typical ’55-’79 blocks place it on the driver side.
1981: The final carbureted engine ever offered for the Corvette is the L81 350. With a Quadrajet carburetor and 8.2:1 compression ratio, it replaces the L82 and standard L48 Corvette engines. It makes 190 hp at 4,200 rpm and 280 lb-ft at 1,600 rpm and is available in all 50 states with either a four-speed manual or three-speed automatic transmission. This is also the final year for the second-generation Camaro, whose optional LM1 350 produces 175 hp at 4,000 rpm and 275 lb-ft at 2,400 rpm.