These changes, plus running the motor at a slightly colder water temperature, increased the power output from the rated 430 hp to 493 at 5,700 rpm and 484 lb-ft of torque at 4,700 rpm. Equipped with the rectangular-port heads, torque production from the 6.2L LS3 exceeded 450 lb-ft from 3,900-5,700 rpm. This gave us a good starting point, but even the stock-displacement LS3 had more to offer.
Though blessed from the factory with impressive head flow, we knew there was more power to be had from this combination. First on the list of any modifications to an LS3 should be a camshaft. With such impressive head flow, the LS3 will respond very well to a more aggressive cam profile. Since our awaiting stroker came from Texas Speed, we hit them up for a cam as well. Taking into account the piston-to-valve clearance offered by the factory components, it supplied a healthy hydraulic roller profile that featured a 0.644/0.614 lift split, a 231/236 duration split and a 112-degree LSA.
Though the cam certainly offered plenty of power alone, we teamed it with a set of CNC-ported L92 heads from Summit Racing. The CNC heads further improved the flow rate of the already good stock LS3 casting. The only thing missing from the ported heads was a suitable spring package, as they were supplied with factory valve springs. Brian Tooley Racing came through with one of its valve spring upgrades. The dual-spring setup eliminated some of the problems associated with a single beehive spring and offered plenty of seat pressure (160 pounds) and open pressure (450 pounds) for our application. The kit also included the necessary titanium retainers, keepers and seals to facilitate the upgrade.
Replacing the heads and cam on the dyno was simple enough, but we did take the liberty of installing new Fel Pro MLS head gaskets and ARP head studs. The CNC-ported L92 heads utilized the factory pushrods, but hardened pushrods would be recommended with the increased valve spring pressure. The factory intake manifold was deemed more than adequate at this power level so it was reused, but dyno testing did require use of a FAST manual throttle body.
With Westech's Ernie Mean still in command of the tune, he quickly had the new combination dialed and styled. When the dust had settled, the modified LS3 produced 569 hp at 6,500 rpm and 522 lb-ft of torque at 5,200 rpm. Though the gains were most prominent higher in the rev range, torque production exceeded 450 lb-ft from 3,600-6,600 rpm. Where the stock motor struggled to produce 484 lb-ft, the new combination exceeded 500 lb-ft from 4,200-5,800 rpm. The ported heads and new cam profile improved power through the entire rev range, but we were anxious to see how it compared to the increased displacement of the Texas Speed stroker.
The final test involved the stroker short-block from Texas Speed. The 418ci displacement was the result of combining a 4.070-inch bore with a 4.0-inch stroker crank. Stuck in the middle was a set of 6.125-inch forged connecting rods and a heck of a lot of precision machining and balancing. The great thing about strokers is not so much the potential for increased peak power (though that is always welcome), but the real reason strokers bring smiles is torque. Increased displacement brings more power everywhere, from right off idle all the way to redline. Though we all brag about the big peak numbers, it is the extra grunt lower in the rev range that can be enjoyed on a daily basis.
To illustrate the gains offered by displacement, the Texas Speed stroker was equipped with the very same components used on the stock-displacement LS3. The TS custom cam and CNC-ported heads from Summit Racing were installed on the stroker. Running the same heads, cam and intake but with 42 more cubic inches produced 609 hp at 6,200 rpm and 570 lb-ft at 5,100 rpm. Compared to the modified LS3, the stroker was up by nearly 40 hp and 50 lb-ft of torque.
The best thing about the added displacement was that the extra 50 lb-ft was available through most of the rev range, from as low as 3,500 rpm. There is no better feeling than stomping on the gas to summon up an extra 50 lb-ft of torque, except maybe having an extra 100 lb-ft of torque, but we'll examine that kind of gain when we add forced induction to the mix. For now, the Texas Speed LS3 stroker was belting out over 600 hp in normally aspirated trim and we have a number of other combinations left to try.
Power Numbers: LS3 Stock vs. LS3 Modified vs Texas Speed Stroker