LS3 Cylinder Head, Cam, and Intake Swap - Crate LS3 Throw Down

These days, opting to build a Mouse motor over an LS small-block probably means that familiarity and practicality both stepped into the boxing ring, and the former won via TKO in the 12th round. With all due respect to the legendary Gen I small-block Chevy, from a horsepower-per-dollar standpoint, it just can’t hang with its LS counterpart. Pricier parts and fear factor used to be the biggest strikes against the LS, but that’s no longer the case. Yank a Vortec 6.0L long-block out of junkyard, swap in a mild hydraulic cam, and you’re looking at an easy 500 hp for well under $2,500. With a plethora of carbureted intake manifolds and MSD’s trick LS ignition controller, you can chuck all that EFI—and the fear that comes along with it—right in the trash. While the Gen I small-block Chevy is the most prolific engine ever conceived in terms of sheer production volume and its impact on amateur and professional racing, each successive iteration of the Gen III/IV design reminds enthusiasts why the General jumped ship to a new platform in the first place.

The proof is in the horsepower. To illustrate the point and test some of the hottest new LS components on the market, we hooked a fresh GM Performance Parts LS3 crate engine to Mast Motorsports’ SuperFlow 902 dyno for a proper WOT christening. While the concept of bolting on a bigger cam, heads, and intake manifold on a crate motor is so cliché in the walk of magazine stories, the results this time around are anything but ordinary. Simply installing a set of Mast’s new 12-degree LS3 cylinder head castings along with a granny-certified 225/231-at-0.050 hydraulic cam netted a gain of 99 hp. That’s not too shabby at all for a naturally aspirated 376 that already puts out 469 hp on stock trim. Throw some more cubic inches and cam into the mix, and the horsepower potential is truly ridiculous.

While the 638hp LS9 and the 505hp LS7 have it handily covered in the power department, the 430hp LS3 used on our dyno session represents the best bang-for-the-buck package in the GMPP crate engine lineup. Currently serving duty in the fifth-gen Camaro SS and the base C6 Corvette, at $6,700 the crate LS3 costs less than half of the price of an LS7. Granted, that’s not exactly pocket change, but it buys a whole lot of motor. Essentially an L92 with a lower profile intake manifold, minus the variable valve timing, the LS3 boasts the same 4.065-inch-bore aluminum block, rectangle-port raised-runner cylinder heads, and 376ci displacement as its Escalade-derived forbear. The combination of a respectable cube’s tally and high-flow heads yield loads of untapped potential, evidenced by the fact that the LS3 produces 430 hp, despite a dinky 204/211-at-0.050 factory cam. Furthermore, the factory’s 430hp rating is quite conservative, as it’s derived using far more stringent SAE testing procedures and correction factor. Under the more conventional Standard Temperature and Pressure standards used by most engine shops, the crate LS3 actually produced 469 hp and 465 lb-ft on Mast Motorsports’ dyno.

The phenomenal airflow capabilities of the Gen III/IV cylinder heads, and GM’s need to keep its cam specs conservative for streetability and emissions purposes, means that tremendous performance gains can be had by simply upgrading to a larger camshaft. Late-model enthusiasts realized this about two days after the first LS1s hit the showroom, but the odds are stacked in favor of hot rodders even more with the LS3. That’s because the 376ci LS3 uses the same camshaft as in the 346ci ’01 LS6, albeit with a smidgen more intake lift. Furthermore, the LS3’s rectangle-port cylinder heads flow roughly 60 cfm more than the cathedral-port LS6 castings (260 versus 320). Considering that its factory cam was originally designed for an engine that’s 30ci smaller and heads that flow 60 fewer cfm, it’s not surprising that the LS3’s torque curve plummets rapidly after 4,700 rpm. To remedy the situation, Mast installed one of its 225/231-at-0.050 hydraulic cams in our test subject, which features 0.602/0.607-inch lift and a 115-degree lobe-separation angle.