Not wanting to reuse the factory...
Not wanting to reuse the factory head bolts and gaskets, we replaced them with a set of ARP studs and Fel Pro MLS gaskets.
To maximize power production...
To maximize power production from the new cylinder heads, we installed a fresh set of E3 spark plugs. Run with the stock ignition and E3 plugs, the modified LS3 never missed a beat.
Equipped with the TEA heads...
Equipped with the TEA heads and cam from Texas Speed, the GMPP LS3 belted out 574 hp at 6,300 rpm and 520 lb-ft at 5,300 rpm.
Since we had some extra dyno...
Since we had some extra dyno time, we elected to try a set of new LS3 head castings from ProComp Electronics. We figured these large-chamber (81cc) heads might be the hot ticket for forced-induction applications. Massaged by Dr. J's, they flow more than 360 cfm on the intake side.
The large chambers on the...
The large chambers on the ProComp heads reduced the compression ratio of our LS3 by 1.3 points, from 10.7:1 to a more boost-friendly 9.4:1. Even so, the combo offered a significant improvement in power over the stock components (538 hp vs 485 hp). Throw on a blower or turbo, and look out.
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.
Boosted Bolt-Ons
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.