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.

Richard Holdener Mar 1, 2010 0 Comment(s)
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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.

Sucp_1003_17 Chevy_small_block_hydraulic_testing Cast_iron_intake_manifold 2/23

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.

Sucp_1003_20 Chevy_small_block_hydraulic_testing Q_jet 3/23

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).

Sucp_1003_18 Chevy_small_block_hydraulic_testing L46_results 4/23

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.

Sources

Comp Cams
Memphis, TN 38118
800-999-0853
http://www.compcams.com
Chevrolet Performance Parts
Detroit, MI 48232
800-577-6888
www.gmperformanceparts.com
Demon Engines
Sante Fe Springs, CA
562-694-2559
www.demonengines.com
Pro Comp Electronics
Ontario, CA 91761
909-605-1123
www.procompelectronics.com
L&R Automotive
Sante Fe Springs, CA 90670
562-802-0443
www.lnrengine.com
Probe Racing
Torrance, CA 90505
310-784-2977
www.probeindustries.com
Sean Murphy Inductions
N.A, AK
714-843-9169
www.smicarburetor.com

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