LS3 Cylinder Head, Cam, and Intake Swap - Crate LS3 Throw Down
Eeking 108 Extra Horsepower out of a Crate LS3 with a Cylinder Head, Cam, and Intake Swap
From the December, 2011 issue of Chevy High Performance
By Stephen Kim
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.
GMPP currently offers three...
GMPP currently offers three different variants of the LS3 in crate trim. In addition to the base LS3 used in our test, it’s also available with a larger 219/228-at-0.050 cam that boosts output to 480 hp and 475 lb-ft. Dubbed the LS 376/480 (PN 191712240), it costs the same as a base LS3. For an extra $600, GMPP matches up a larger 226/236-at-0.050 cam with a single-plane intake manifold to create the LS 376/515 (PN: 19171225), which increases performance to 515 hp.
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.
Like many modern camshaft...
Like many modern camshaft designs, the Mast unit packs steep ramps onto its billet core with 0.602/0.607-inch lift spread over a rather tame 225/231 degrees of duration at 0.050 lift. This allows taking advantage of the high-lift flow numbers of the LS3 heads without sacrificing streetability. Since the cam was designed primarily for EFI applications, its wide 115-degree LSA enhances engine vacuum and smooths out idle quality.
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.
Along with the cam swap, Mast...
Along with the cam swap, Mast installed its nitrided 1.290-inch springs onto the stock LS3 heads to handle the extra valve lift. They feature 130 pounds of seat pressure, 318 pounds over the nose, and are good for up to 0.650-inch lift. The springs are direct stock replacements that are compatible with the stock retainers and locks, and are sold as a package with the Mast cam for $680.
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.
Mast’s LS3 head castings are...
Mast’s LS3 head castings are available in three different trim levels for small- (3.900 to 3.930), medium- (4.000 to 4.070), and large-inch bore (4.125 to 4.200) motors. The small-bore heads have 253/89cc ports and 2.080/1.600-inch valves, the medium-bore heads utilize 256/89cc ports and 2.165/1.600-inch valves, and the large-bore heads offer 270/87cc ports and 2.200/1.600-inch valves. Prices for a fully assembled set—which includes factory GM rocker arms and Mast rocker stands—start at $3,600. That’s not cheap, but there’s no denying the tremendous volume of air they move.
The ports and combustion chambers...
The ports and combustion chambers on the Mast heads are fully CNC machined prior to shipment. Flatting out the valve angle from 15 to 12 degrees not only helps de-shroud the valves, but it also yields a smaller, more efficient, and faster-burning combustion chamber design. Customers have the option of choosing between solid- and hollow-stem steel valves, and our test heads were fitted with the latter.
Although airflow could have...
Although airflow could have been increased significantly by raising the intake ports to complement the flatter valve angle, Mast opted to leave them in the stock location to maintain compatibility with factory intake manifolds. Mast’s small-, medium-, and large-bore heads flow 353/257, 370/241, and 390/249 cfm, respectively, at 0.700-inch lift. Those figures were achieved using appropriately sized 3.900-, 4.070-, and 4.125-inch bore fixtures for each trim level of head.