Even the competition has to agree, Chevy's LS-engine family is more than just a worthy successor to the original small-block; it's one hell of a motor. The Blue Oval boys are jumping up and down about their new 5.0L, but (as usual) they are still behind the eight ball in terms of displacement and power output. While the new four-valve 5.0L mod motor offers reasonable high-rpm power, it is decidedly lacking in low-speed power compared to the LS3. Credit the 6.2 liters of displacement for all that wonderful torque. High rpm power is all well and good, but the vast majority of spirited (street) driving comes lower in the rev range. Besides, in the LS3 there is no choice between low-speed and high-rpm power, as the GM motor offers both. Toss in the fact that the LS3 features lightweight, all-aluminum construction, a composite intake, and even variable cam timing (in the automatic/L99 version) and you have a small-block with all the technology of a DOHC motor, without the penalties in size, weight, and complexity. Back in the original muscle car era, it took a big-block to muster power ratings that exceeded 400 hp and a like amount of torque-using those old (gross) power ratings and not net! The modern LS motor makes this a good time to be a Chevy owner.
The LS engine family has evolved constantly to keep GM ahead of the competition. The original LS1 was a solid step above the LT1, just as the LT1 easily eclipsed the performance of the previous L98 TPI motor. In its latest form, the LS3 has followed the 5.7L LS1/LS6 and 6.0L LS2 engine configurations by starting with an increase in displacement, checking in at 6.2 liters. This came courtesy of an increase in bore from 4.00 inches (in the LS2) to 4.065 inches, though the two shared the same stroke of 3.622 inches. The increase in bore size not only upped the displacement, but also airflow, as head flow increases with bore size. Combine this with a revised cylinder head that replaced the cathedral-port design with a more conventional rectangular port, and you have the makings of one serious small-block. Tested on the flow bench, production LS3 heads flow as much as 315 cfm right out of the box. Not long ago it took a pretty serious 23-degree small-block head to achieve these same flow numbers, offered by the stock LS3. Despite flow figures that suggest supporting over 600 hp (we recently made 690 hp with a set of stock LS3 heads on a 468 stroker for our sister book Hot Rod), additional flow is available with proper porting. What we wanted to find out was just how much power was available with a set of ported LS3 heads.
The massive head flow offered by the stock rectangular-port heads means the LS3 responds favorably to cam swaps (Ed note: "favorably" is an understatement!). The flow potential of the stock heads allowed GM to reach its power goals for the production LS3 using relatively mild cam timing, akin to the early LS6 (and LS2) grind. Using the same 204/211 duration split (measured at .050), the stock LS3 cam offers .551/.522-inch lift with a wide lobe separation angle of 117 degrees. This combination of mild cam timing and sizable head flow means the LS3 motor is just begging for wilder cam timing. Think of the LS3 as an all-aluminum race motor without the race cam. Swapping in the right cam will literally transform your mild-mannered stock motor into a street screamer, but where does that leave ported heads? Will even more head flow improve the power output with the stock cam? Are the gains offered by ported heads greater after you've performed a cam swap? Is porting worth the extra expense? That's what we came to find out.
To illustrate the potential lurking in the LS3, and to answer the cam versus cylinder head question, we embarked on a series of tests using a GMPP LS3 crate motor. Performing the multi-head and cam swap on the engine dyno was much easier than had the LS3 been installed in a '10-or-newer Camaro. To illustrate the gains offered by both head and cam swaps, we ran the GMPP LS3 crate motor on the engine dyno in stock trim, then after the installation of a set of GMPP CNC LS3/L92 heads followed by a Comp LSr hydraulic roller cam. To finish things off, we installed one final set of dedicated LS3 castings from ProComp Motorsports. This way, we compared ported stock castings to a set of (affordably priced) aftermarket LS3 heads. Before we could run the GMPP LS3 on the engine dyno, a few changes were necessary. Off came the factory drive-by-wire throttle body and on went a more dyno-friendly manual throttle body from FAST. The stock exhaust manifolds were also replaced by a set of 1 3/4-inch, long-tube headers. The production water pump was likewise ditched in favor of a Meziere electric unit (the LS3 ran sans accessories).