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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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.

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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?




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