By 1965, new Corvette buyers fell into two distinct groups: the hands-on set and the showboaters. A key determinant was the engine option they chose. The hands-on guys tended to be weekend warriors who loved resetting valve lash after a day at the track. They pointed with pride to the 8,000-rpm tachometers and 6,500-rpm redlines in their cars. The other group preferred clean hands and ordered engines from the bottom half of the Corvette option sheet. Here, hydraulic cams ruled and tach faces only read to 6,000 rpm, redlines to 5,000.
But that changed in 1965. For a mere $107.60 over the base 250hp 327, the new L79 offered both Corvette shoppers something attractive and new. With 350 hp at 5,800 rpm, the L79 was only 15 hp shy of the hottest carbureted 327, the L76 with 365 hp at 6,200 rpm. And with 360 lb-ft of torque at 3,800 rpm, the L79 actually had 10 lb-ft more torque than the L76.
The groundbreaking aspect of the new L79 was the hydraulic cam. With its oil-filled, multipiece lifters (aka tappets), the L79 didn't require the frequent valve lash adjustment of its more potent big brothers. But the L79 was no cheap imitation. Aside from the "juice" cam, it was a mechanical copy of the Corvette's L76 and shared the same forged 11.1:1 pistons, 585-cfm 4150 series Holley four-barrel, aluminum dual-plane intake manifold, enlarged 6-quart oil pan, high-flow air cleaner unit, and new-for-1963 big-port "camel hump" cylinder heads with 2.02/1.60 (intake/exhaust) valve heads.
The L79's cam lift specs checked in at 0.447/0.447 versus the L76's 0.485/0.485. Overlap and duration were also somewhat relaxed.
Another L79 first was the ability to accommodate factory C60 air conditioning. By contrast, GM barred C60 A/C equipment on all Sting Rays built with solid-lifter engines. This undoubtedly torpedoed a lot of would-be sales. But thanks to a milder hydraulic cam and free-breathing heads and induction, L79 buyers could indulge in the wonders of Frigidaire—and did.
Unlike certain Corvette engine options that were never offered in other Chevrolet passenger cars, the L79 was also available in 1965-1968 El Caminos and Chevelles (non-SS after 1965), 1966 Chevy IIs, and the redesigned 1968 Chevy Nova. Also scattered into the mix were six 1967 Chevy IIs and (perhaps) a handful of 1967-1968 Camaros packing the deceptively potent L79. In most non-Corvette applications, marketing concerns shuffled the L79 to 325 hp despite the retention of all major mechanical details.
What is assured is that GM built 49,034 L79-powered vehicles during the four-year production run (1965-1968). For fascinating info on rare combinations and helpful facts and trivia, check out the L79 Registry (l79registry.macswebs.com. There you can read about oddball L79 installations with three-speed manual transmissions, four-door body styles, and more.
Now let's follow the team at R.A.D. Auto Machine in Ludlow, Massachusetts, as it revives and dyno tests a nearly stock 1966 Corvette L79 powerplant. Will it deliver on its promise of 350 hp? And what impact will a set of headers have on things?
1 Born to a 1966 Sting Ray, the block’s 4.00-inch-diameter cylinders were enlarged by 0.040 inch to remove wear. The 3.250-inch stroke remains unaltered, bringing displacement to 331 cubes. Note the integrally cast recesses at the cylinder bore bases. They arrived in 1962 to clear the quarter-inch of extra stroke (and 0.125 inch overbore) that grew the 283 into the 327.
2 The L79 shared the L76’s 53.2-pound forged crank. In 1968 the bearing journal diameters were enlarged from 2.30 to 2.45 (mains) and 2.00 to 2.10 inches (rods). To remove worn surface material, both journal diameters were reduced by 0.010 inch.
3 Before the 1968 model year, all small-blocks used two-bolt main caps, even the exotic L84 fuelie. Here, R.A.D. Auto Machine honcho Donnie Wood tightens the cap bolts to 70 lb-ft. Clevite bearings (PN MS-429P-10) are set with 0.0020 to 0.0022 clearance.
4 The stock 5.7-inch forged rods were resized and fitted with fresh 11/32-inch fasteners. Clevite also supplied the rod bearings (PN CB-745P-10) with clearance set at 0.0018 to 0.0020 inch. Forged dome-top pistons are from Icon (PN IC793-040) and reproduce the L79’s 11.1:1 compression ratio.
5 One minor deviation from factory L79 specification are the thinner 1/16-inch top (moly faced) and second (cast) rings for reduced friction. Stock items are 5/64-inch (top and second). Gaps are set at 0.018 and 0.020 with stock tension oil-control ring packs. Wood says, “The thinner rings are a nice bonus but are used here because many modern piston makers have switched to this more commonly available metric ring size.”
6 As growing numbers of muscle car restorers seek a faithful driving experience, right down to the muffler tone, general-purpose aftermarket cams no longer cut it. The Speed Pro (PN CS 179R) is a virtual clone of the OE GM L79 hydraulic, flat-tappet grind. Specs are 0.447/0.447 lift, 291/291 advance duration, 222/222 duration at 0.050, with a 114-degree LDA.
7 Knowing to steer clear of any timing chain with split-seam rollers, Wood degreed the cam, then installed a three-bolt timing set from Liberty Performance (PN LT98100).
8 Small-block oil pickup tubes are press fit and can invite air suction leakage at the pump body. This slick driving tool ensures full engagement without bending, denting, or kinking the fragile tube. The pump is a high-volume Melling (PN M-55A), as is the tube (Melling 55-S3). A Melling hard-tip pump drive shaft (PN IS-55E) ensures longevity.
9 Though Chevrolet never offered the 1965-1968 L79 in Camaros, fullsize cars, or light pickups, it motivated many non-Corvette models. Only Corvette applications got this special 6-quart pan with spring-loaded baffles. Corvette also had the only L79 with finned aluminum rocker covers. The rest got chrome-plated stampings with the Chevrolet logo.
10 The big port 461/camel hump head (casting number 3782461) arrived with the 327 in 1962 with 1.94/1.50 (I/E) valves. For 1964, all-out versions of the 327 (including the 375hp L84 fuelie) got 2.02/1.60 valves, and a star was born. The R.A.D. team spent a few extra minutes with the “bowl hog.” The pen indicates where a quick plunge cut eliminated the flow-disturbing flange left by mass production techniques.
11 The stock 2.02/1.60 (I/E) valves were replaced by lighter Super Street stainless ones from Liberty Performance (PN TX-202/TX-160, I/E). Back-cut and swirl-polished, they retain stock 11/32-inch stem diameters. Fresh bronze wall guide inserts perfectly align the moving parts. Beyond the bowl work, no other port grinding was performed.
12 Liberty Performance single valve springs with surge dampers (PN LRV 943-X-16) deliver 125 pounds of pressure closed and 285 pounds at 0.450-inch lift. The 0.030-inch thickness of the stock stamped metal oil shrouds (top) was calculated into the 1.700-inch installed height. The guide bosses were also machined for PC-style valve seals. Notice the screw-in rocker arm stud holes, a standard L79 feature.
13 Our 0.010-inch-deck-cut, 0.042-inch-thick Fel-Pro composite head gaskets, and L79-clone pistons deliver a true 11.1:1 compression ratio. The ARP pushrod guide plates utilize the factory-installed threaded rocker arm stud holes. Head bolts torque to 65 lb-ft. Stock-diameter, 0.311-inch pushrods are used.
14 Built before the 1969 arrival of sealed PCV systems, the 1966 L79’s lifter valley oil separator canister feeds the road draft tube via a passageway machined into the block. If it’s clogged or missing, an oily mess results. This system allowed Corvette’s gorgeous finned rocker arm covers to remain free from ugly oil-fill caps and PCV valve orifices for so many years.
15 Part of the L79’s high-revving nature is this lightweight 8-inch crank damper. Shared with solid-lifter Corvette 327s, the 12 fanlike ribs don’t move air. Rather, the configuration gives the center hub the strength it needs while trimming more than a pound of unnecessary mass.
16 Chevy small-block designers Ed Cole, Harry Barr, and others shared the 265’s pivoted ball studs and stamped-steel rocker arms with the all-new 1955 Pontiac V-8. On Chevys, the same simple rocker arm interchanges between hydraulic and solid-lifter camshafts; all that differs is the lock nut! By contrast, competing adjustable rocker arms were typically forged steel and shaft-mounted, and required complex adjustment screws and nuts. The Chevy/Pontiac configuration was much lighter.
17 Resting atop the original Winters foundry dual-plane intake manifold (casting number 3844461), the rebuilt Holley R3367A packs No. 64 primary jets and a No. 39 secondary metering plate (equal to No. 69 jets). In background, Donnie Wood at R.A.D. Auto Machine displays the quartet of 1.550-inch throttle blades and vacuum-operated secondaries.
18 Corvette-bound L79s were the only ones equipped with a tach-drive distributor. The stock single-point components are acceptable but were exchanged for a PerTronix Ignitor II breakerless conversion kit for longevity (PN 91181).
19 Rather than hassle with accessory drive pulleys and belts, an electric dyno water pump was used for all testing. Truth be told, before the advent of scrutiny from the Society of Automotive Engineers (SAE), Detroit dyno testing of the 1950s and the muscle car era often excluded accessory drives. With a standard water pump and alternator added, our observed output would likely drop 15-20 hp.
20 Exhaling through reproduction Dorman “ram’s horn” exhaust manifolds, the accessoryless L79 registered 361.6 hp at 5,600 rpm and 401 lb-ft of torque at 3,700 rpm. This validates Chevrolet’s advertised claims of 350 hp at 5,800 rpm and 360 lb-ft at 3,800 rpm. Priced a mere $70 per side (PN EX-646 left, EX-647 right), the generic manifolds lack casting dates but suffice for a daily driven restoration. Their 3-inch outlet diameter is correct for L79, L76, and L84 applications. Base and 300hp (L75) Corvette manifolds used smaller, 2 1/2-inch outlets.
21 Headers have always been a popular day-two addition, and for good reason. The progressive primary tubes of the Hooker Super Competition under-chassis units begin at 1 3/4 inches, grow to 1 7/8 inches in diameter, and terminate in 3-inch collectors. Initially, the scavenging effect caused a lean mixture. When the primary jets were enlarged from No. 64 to No. 68 and the secondary plate left alone at No. 39 (comparable to No. 69 jets), the resulting 12.92:1 air/fuel ratio yielded 391 hp at 5,500 rpm and a heady 422.6 lb-ft at 3,500 rpm.