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Dyno Testing chevy's Famous Hydraulic Cammed Small Blocks - Legendary Small-Block Shootout-The Sequel

This Month We Test Hydraulic Horsepower: It's L79 Vs. L46 Vs. L82.

By Richard Holdener, Photography by Richard Holdener

The continuation of this series came about after a letter from reader John Tremul requesting we take a look at another set of serious small-blocks. The primary difference between these and the previous legendary trio (September 2009 Super Chevy) is cam timing. Where the L76, DZ302 and LT-1 were factory equipped with solid-lifter cam profiles, the L79, L46 and L82 were equipped with the more user-friendly hydraulic flat tappet cams. While the solid-cammed small-block owners might be tempted to look down their noses at mush-bucket mice, the L79-powered Chevy II is regarded as one of hottest and quickest factory muscle machines ever produced.

Both the L79 and the larger displacement L46 of '69-70 were factory rated at 350 hp. Remember these were the gross ratings where the L82 (the '73 replacement for the LT-1) was rated at just 250 net hp. For you alpha-numeric freaks, think of the L46 as the 350 ci version of the L79 327 and L82 as a low-compression version of the L46 (and not unlike the '71 version of the LT-1 we tested in part 1). As in part 1, we wanted to see how these hot hydraulic small-blocks compared to each other (given the displacement difference between the 327 and 350) and how the drop in compression hurt the later L82.

Before getting to the test, a little background is in order. Despite my Chevy upbringing (and the fact that my first car was a '70 RS Camaro), I can say that until we received the letter from Tremul, I was unfamiliar with the L46 engine designation. I knew the history and popularity of the L79 and even the L82 (as well as all of the solid-lifter small-blocks), but the two-year (Corvette-only) production of the L46 had somehow escaped me. On the plus side, this gave me another opportunity to research, build and test yet another Mouse.

The L79 was essentially the solid-lifter L76 (365-hp 327) with a cam swap. The two engines shared the same compression, big-valve heads and aluminum intake. The question now was just how much power (if any) did the L79 lose by replacing the Duntov 30-30 cam with the hydraulic L79 stick? Judged on specs alone, the drop in cam timing was pretty significant. The 30-30 cam offered 0.485 lift and 254 degrees of duration (measured at the now industry standard of 0.050). This compares to the 0.447 lift and 221 degrees of duration offered by the L79 cam. Of course you must also take into account that the L79 cam specs were net while the 30-30 cam specs were gross, and (as such) would be slightly less once you backed out the lash specs (especially if you ran the valve lash at the specified 0.030).

Just as Chevy had done when it replaced the L76 327 with the LT-1 350, it altered the cam timing for the larger motor when it created the 350hp L46 350. The change in cam timing wasn't dramatic, but it is worth mentioning that the L46 received a hydraulic flat tappet cam with 222 degrees of duration and a dual-pattern lift split of 0.450/0.460, both slightly more than the L79. Both the L79 and L46/L82 cams shared the same 114-degree lobe separation angles, but the two offered different intake centerlines and overlap figures. You will remember from part 1 that Chevy reduced the intake cam timing on the solid lifter LT-1 compared to the previous 302 (and L76), but they actually increased the lift and duration (albeit slightly) on the L46 compared to the L79.

Another difference between the L79 and L46 was the induction system. Where the L79 featured a dual-plane, high-rise aluminum intake and (small) Holley carburetor, the L46 was equipped with a cast-iron, low-rise (for Corvette hood clearance) manifold and a 765 cfm Rochester Quadrajet carburetor. Though everyone immediately thinks Holley when you start talking about performance, the Q-jet used on the L46 actually out-flowed the small Holley on the L79. Would this additional airflow translate into a power advantage?

By comparison, the L82 was essentially a low-compression L46, as emission regulations eventually resulted in an across-the-board drop in static compression ratio (from 11.0:1 to 9.0:1). The net power rating of the L82 ranged from a high of 250 hp to a low of 205 hp ('75) during the eight years of production ('73-80). Just how would the 250hp (net) L82 compare to the 350 hp (gross) rating of the L79 and L46? That's what we were here to find out.

L79 350-HP 327
First up was the 350hp L79 327. The build up of this motor was a simple matter of replacing the solid Duntov 30-30 cam in our L76 327 with the GM Performance Parts L79 grind (PN 3863151), or so we thought. A call to GM revealed that only the L46 cam was still available and we had to shop elsewhere for the L79 stick.

Leafing through the Comp Cams catalog revealed that it indeed offered a reproduction of the factory L79 cam under the Factory Muscle heading (PN 12-1060-3). Retained were the 461 intake, the 186 fuelie heads and 11.0:1 compression ratio. As with our previous trio, we ran all three of these hydraulic cammed small-blocks with a set of 1 3/4-inch long-tube headers. We used a Holley 750 HP-series carburetor (larger than the factory Holley originally run on the L79) so this definitely gave it an advantage. (The L46 and L82 were run with a Rochester Quadrajet supplied by Sean Murphy Inductions.)

It is likely that the 750 Holley helped the L79 more than the previous solid-cammed combinations as the L79 was equipped with a smaller carburetor than the 780s (4150) used on the LT-1 and 302. Because of the number of letters received on the subject, we also took the liberty of replacing the 6.0-inch connecting rods and attending pistons with the factory-length 5.7-inch rods.

The dome design was identical, the only change was the compression height on the piston. Before making the swap to L79 specs, we ran the L76 with the new piston/rod combination to register the difference between the different rod lengths. The graphs were identical with less than 1-2 hp difference anywhere in the curve. Basically we did a lot of work for nothing, but nothing is too good for the readers of Super Chevy.

With our back up work performed, it was time to run the L79. We installed the Comp L79 grind and matching hydraulic flat-tappet lifters along with a can of high-zinc break-in lubricant from Lucas Oil. Naturally the cam and lifters were liberally coated with a moly-based assembly lube prior to installation and we allowed the new cam plenty of break-in time (keeping engine speed above 2,000 rpm) prior to making our power pulls. After dialing in the ignition timing and carb jetting, the L79 produced peak numbers of 345 hp at 5,400 rpm and 381 lb-ft of torque at 3,900 rpm. Torque production exceeded 375 lb-ft from 3,400 rpm to 4,400 rpm and exceeded 350 lb-ft from 3,000 rpm (and lower) to 5,100 rpm.

The 327 produced peak power at just 5,400 rpm with the hydraulic flat-tappet cam, but remained relatively flat out to 6,000 rpm, dropping by only 12 hp. We were not surprised by the torque production of the hydraulic-cammed 327 (compared to the previous solid-cammed L76), but we were surprised to see the peak power numbers produced by the L79. Despite a drop in cam timing of over 30 degrees (at 0.050) compared to the Duntov 30-30, the L79 still managed to produce just 10 hp less than the L76. No doubt, the larger carb helped, but it is no wonder the L79s had such a strong reputation on the streets back in the mid-late '60s.

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.

As luck would have it, the L82 was equipped with the same hydraulic flat-tappet cam as the L46. The difference between the two motors was the static compression ratio. Where the L46 featured the small-chamber, big-valve fuelie heads (186 casting numbers), the L82 came with large-chamber (882 casting numbers) heads. Remember that our '71 LT-1 performed very well with a set of the 76cc chamber smog heads, despite the significant drop in compression. It all depends on how well they flow, which is a function of several factors including core shift, valve job and a variety of other production-line variables.

In addition to the larger combustion chambers, the L82 also received a piston change compared to the L46. Gone was the domed LT-1/L46 forged aluminum pistons, replaced by a flat-tops with valve reliefs, dropping the compression down by two full points (from 11.0:1 to 9.0:1). This was a mistake we made when running the 1971 version of the LT-1 in our previous test, as the '71 version also received a similar piston and not just the head swap. Lucky for us, Westech had a flat-top 350 small-block on hand and we produced the L82 by adding a set of freshly machined 882 heads (from L&R Automotive), the GMPP L46 cam and the Q-Jet induction system.

The drop in compression ratio really took its toll on the power output, as the L82 produced peak numbers of 313 hp at 5,500 rpm and 355 lb-ft at 3,800 rpm. As a rule of thumb, each point of compression ratio is worth roughly four percent in power. Dropping two full points meant a loss of eight percent relative to the L46, but our drop was slightly more significant. Though freshly machined, the 882 heads did not flow quite as well as the 492 fuelie heads used on the L46 (down by 8-10 cfm at various lift points).

What did we learn from this test? The results indicate that the L79, L46 and L82 were all accurately rated by GM in terms of power output, despite the difference in the gross and net power ratings. Not surprisingly, the larger L46 350 offered more power and torque than the smaller 327. The power output of our L79 327 was likely helped by the 750 Holley compared to the original 600 cfm version, but we wanted to test all of the factory Holley-equipped motors with the same carb (as used on the L76, LT-1 and 302 motors).

Though you don't often associate cast-iron intake and Q-Jet carb with performance, the induction employed on the L46 and L82 actually out-flowed the smaller Holley on the L79. We'd have a hard time running a cast-iron intake on any street engine these days, but know that if you are building an original 350hp 350, the induction system is pretty darn good. The drop in compression really hurt performance on the L82, but we expected as much.

What really surprised us was just how well the hydraulic-cammed L79 and L46 did compared to their solid-lifter counterparts from part 1 (L76 and LT-1). Though there is no denying the sound of a high-compression small-block equipped with a solid-lifter cam, the performance of these hydraulic motors was every bit as legendary.

Probe Racing
2555 West 237th Street
CA  90505
Demon Engines
Sante Fe Springs
1801 Russellville Road
Bowling Green
KY  42101
Sean Murphy Inductions
L&R Automotive
13731 Bora Drive
Sante Fe Springs
CA  90670
Comp Cams
3406 Democrat Road
TN  38118
GM Performance Parts
P.O. Box 33170
MI  48232
Pro Comp Electronics
605 S Milliken Avenue
Unit A
CA  91761
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By Richard Holdener
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