As powerful and efficient as the Corvette's 6.2L LS3 engine is, there's always room for improvement. This unrealized potential is perhaps most evident in the cam timing, which is relatively mild (0.551/0.524-inch lift, 204/211-degree duration, 117-degree lobe-separation angle) given the cylinder heads' enormous flow potential. We decided to see how much extra power could be unleashed by installing a rowdy high-performance replacement stick from Texas Speed & Performance (0.641/0.615-inch lift, 231/236-degree duration, 111-degree LSA). Because of its aggressive nature, this cam is recommended for manual-trans vehicles or automatics with a 2,500-rpm-stall torque converter. (It's also available with a slightly wider lobe separation for improved idle quality.)
Running a cam change in an LS3 is a no-brainer, but for us it simply wasn't enough. Just as we did a few years back with an LS2, we decided that the LS3 deserved a set of basic performance modifications to illustrate what is possible with the right combination of parts. To that end, we sourced an LS3 crate motor from GM Performance Parts and subjected it to the usual array of upgrades. In addition to the aforementioned cam, we bolted up a set of ported L92 heads from the flow wizards over at Total Engine Airflow (TEA). According to the company, the CNC porting procedure took the already impressive L92 heads from 315 cfm at 0.700 lift (327 cfm at 0.600) to an even more impressive 371 cfm.
In addition to the porting, the TEA heads featured a 2.165/1.590 valve package. Naturally, they were treated to a multi-angle competition valve job and a "Platinum" valvespring package capable of supporting our 0.641-lift cam all the way up to 7,000 rpm without fear of valve float. To further improve rpm capability, the heads also featured titanium retainers and hollow-stem LS3 intake valves.
Before we could begin, our GMPP LS3 crate motor needed to have a few items replaced to prepare it for dyno use. The throttle body was supplanted by a manual unit from FAST, the exhaust manifolds were ditched in favor of a set of 1 3/4-inch long-tube headers, and, since we weren't running any accessories, the water pump was pulled in favor of a Meziere electric unit. Once we had the crankcase full of Lucas oil (conventional for the break-in procedure), the LS3 crate motor was up and running in no time. After the break-in procedure, the motor was run in stock trim with the headers, the electric water pump, and a set of E3 spark plugs. So equipped, the GMPP LS3 produced 485 hp at 5,900 rpm and 476 lb-ft of torque at 4,600 rpm. Torque production from the 6.2L exceeded 450 lb-ft from 4,100 rpm to 5,600 rpm.
After establishing a baseline, we tore into the crate motor to make way for the new cam and heads. The head swap required the removal of the factory coil packs, valve covers, and rockers, while the damper, front cover, and timing chain were all that stood in the way of accessing the cam. Because we were using ported factory heads, there was no need to change pushrod length. The L92 heads supplied by TEA also offered stock valve stem and spring-installed heights, so all we had to do was bolt down the factory rockers. Since the factory head bolts are not reusable, the new heads were secured using ARP studs and Fel Pro gaskets.
Replacing the factory LS3 cam with the custom Comp grind from Texas Speed also required replacing the timing (cam) gear. The factory LS3 cam is run with an upper cam gear retained by a single bolt. By contrast, most aftermarket cams come with the more common three-bolt core and, as such, require a new cam sprocket designed to work with both the front-mounted LS3 cam sensor and the three-bolt cam. This sprocket is available from Texas Speed or directly from GM (PN 12586481) for less than $30.
After the head and cam swaps, everything was buttoned back up, and the motor was once again ready to run. With the TEA heads and Texas Speed cam upgrade, the LS3 really came alive. These performance upgrades increased the output of the LS3 to 574 hp at 6,300 rpm and 520 lb-ft of torque at 5,300 rpm. The engine pulled cleanly all the way to 7,000 rpm, where it was still producing 550 hp. Torque production from the 6.2L now exceeded 500 lb-ft from 4,300 rpm to 5,800 rpm, making for one sweet torque curve.
The stock LS3 is already near the top of the current crop of performance V-8s. That you can add nearly 100 hp to this already impressive package with a simple head-and-cam swap is remarkable, a true testament to the Power of 3.
GMPP LS3 vs. TSP Cam and TEA L92 Heads
As important as the huge jump in peak power (from 485 to 574 hp) is the significant improvement in torque production (from 476 to 520 lb-ft) throughout the rev range. These gains are even more impressive when you consider that the TEA heads came equipped with slightly larger combustion chambers than did the stock LS3 units (70cc vs. 68cc), dropping the static compression by nearly 0.2 points.
GMPP LS3 vs. TSP Cam and Dr. J's 81cc ProComp Heads
Despite dropping the compression ratio from 10.7:1 to 9.4:1, the ported ProComp heads and Texas Speed cam improved the output of the LS3 crate motor from 485 hp and 476 lb-ft of torque to 538 hp and 495 lb-ft. Knowing that every point of compression drops power output by 4 percent, we can calculate that with the stock chamber size, these heads would produce in the neighborhood of 565-570 hp. A full test of the standard-chamber heads will be completed soon, but for now it's clear that these large-chamber offerings combine plenty of flow with a drop in compression that makes them ideal for forced induction.
We took a set of large-chamber L92 heads from ProComp and had Dr. J's "tune them up" so we could run them on our LS3 (see graph). Thus modified, the ported ProComp heads offer impressive flow numbers, enough to support more than 700 hp in normally aspirated trim. Combine that with the drop in compression, and you have some seriously powerful blower heads. ProComp also offers LS3 heads in standard chamber sizes for the NA crowd, and Dr. J's can tune them for big-time power production.
If you're considering a supercharger or turbo for your LS3, here's an interesting option to explore: ProComp Electronics now offers dedicated LS3 head castings in as-cast and CNC-ported form. What makes them so attractive for forced-induction applications is that they're available with combustion chambers measuring 80-81 cc's, compared with just 68-70 cc's for the production LS3/L92 heads. The larger chambers drop the compression ratio by 1.3 points, bringing it down to a more boost-friendly 9.4:1.