LS3 Cam and Cylinder Head Swap - Late Crate Update

Swapping the heads and cam on an LS3 can yield some significant power gains.

Let's face it, not all crate motors are created equal. In a world in which remachined, remanufactured, and reconditioned all blur into one seemingly unremarkable product, it is refreshing to see that the word new still applies. Nowhere is this more evident than in the current lineup of crate engines available from GM Performance Parts. Using our LS3 as an example, the combination is essentially a brand-new Corvette LS3 plucked from the assembly line. Rated at 430 hp and 424 lb-ft, the LS3 crate engine has more going for it than just the impressive power output. How many crate engines can offer the level of research and development and attending reliability that went into a production engine? Corvette owners fully expect an LS3 to run flawlessly for 100,000 miles or more. You'd be hard pressed to find that level of engineering in any other crate motor that didn't originate at the OEM level.

Starting with an increase in displacement, the LS3 checks in at 6.2 liters (376 ci) versus the previous 6.0L LS2 combination. This comes courtesy of an increase in bore from 4.00 inches (in the LS2) to 4.065 inches, while the two share the same stroke of 3.622 inches. 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 a serious small-block. The production LS3 heads flow more than 315 cfm right out of the box.

The GMPP crate motor was essentially a 6.2L LS3 Corvette mill. Rated at 430 hp and 424 lb-ft, in the right chassis, the LS3 offered 11-second performance even in stock trim.

The GMPP crate motor was essentially a 6.2L LS3 Corvette mill. Rated at 430 hp and 424 lb-

The massive flow potential of the LS3 heads allowed GM to reach its power goals for the production LS3 using relatively mild cam timing. GM went back to its successful (early) LS6 grind and applied it to the LS3. The stock LS3 cam offers a 0.551/0.522 lift and 204/211 duration at 0.050 with a wide lobe-separation angle of 117 degrees. The combination of this mild cam timing and the impressive LS3 head flow means the LS3 motor will respond very favorably to cam upgrades. To illustrate the potential lurking in the LS3, we applied a select few factory performance upgrades to our GMPP LS3 crate motor. We chose a set of GMPP CNC-ported LS3/L92 cylinder heads and a roller cam. What we liked about the GMPP heads was that not only did they offer exceptional flow numbers (see flow data), but they were also a trouble-free bolt-on because they were essentially factory components. Recognizing the mild factory cam specs, we also opted to replace the wimpy factory LS3 cam with a much more performance-oriented stick from Comp Cams.

The factory drive-by-wire throttle body made way for a manual FAST 102mm Big Mouth throttle body.

The factory drive-by-wire throttle body made way for a manual FAST 102mm Big Mouth throttl

Those who have jumped ahead already know the combination offered sizable power gains, but before getting to the dyno numbers, there were a few installation tricks that bear mentioning. 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 with a set of 13/4-inch, long-tube headers. The production water pump was likewise ditched in favor of a Meziere electric unit (the LS3 was run sans accessories). All testing was run with the stock injectors controlled by the FAST XFI management system. After filling the crankcase with Lucas 5W-30 (nonsynthetic) oil, the motor was treated to a break-in procedure prior to running in anger. After the break-in and some quick tuning by Westech's Ernie Mena, the LS3 belted out some pretty impressive numbers. Torque production exceeded 450 lb-ft from 3,900 rpm to 5,700 rpm and more than 400 lb-ft from 3,000 rpm to 6,300 rpm. These are the kind of numbers we'd expect from a 383 stroker small-block with a healthy cam, free-flowing aftermarket heads, and a good dual-plane high-rise.