TPIS LSX 383 - Warning Shot

TPIS began the development of the Engine Masters Challenge entry with a clean sheet, and discussed all of the relevant points and variables as a team. We agreed on just about everything, from the critical cylinder head choice to some loose camshaft and intake basics. Surely we'd have some variables to figure out and fine-tuning to accomplish, but the major hardware choices were narrowed down almost immediately.

Beginning with a GM LSX block, we knew the foundation of our Challenge entry would be a solid one. The LSX block is designed to support big power, and the additional strength in critical areas would ensure we didn't have any issues here. We know LSX blocks have shown the capability to withstand 2,000 hp, and our target peaks would be less than half of that. We simply wanted an absolutely rock-solid foundation to build upon, and we got it with the LSX.

Once we completed flow testing, we settled on the 383ci displacement level as one the heads were fully capable of feeding. Team leader Myron Cottrell says: "I wanted to keep displacement under control. It would have been easy to stroke the engine out to over 420 cubes and produce some big numbers, but we had to focus on efficiency here. The valves needed to be completely unshrouded, but it's easier to get horsepower-per-cubic inch efficiency from lower displacements, and we knew there would be a size limitation on the exhaust pipe diameter. This meant all the competitors would be breathing through the same diameter exhaust pipes, so a smaller displacement engine should have some advantage over a larger one breathing through the same pipe in this rpm range. [3,000-7,000 rpm-ed.] The 383 displacement would be able to make good torque, and with the single-plane intake manifolds we were considering, we knew it could make good power right up to the 7,000-rpm ceiling."

The intake manifold was the next major component to choose. We considered all the factory-type (front-fed) and traditional (top-fed four-barrel type) intakes that were commercially available and legal for use in the competition. We decided that the four-barrel style would be best, and ended up testing several different types before settling on the Edelbrock Super Victor. We learned that the longer the runners were, the greater the power and torque potential existed in the target EMC rpm range of 3,000-7,000 rpm. This greater-length theory extended right up into the throttle body, as our testing showed greater returns from taller examples. TPIS manufactures several different throttle bodies for use in these configurations (mounted like four-barrel carbs on EFI applications) and the tallest one delivered the best results. In fact, the 102mm "tall" TPIS throttle body was some 20 lb-ft better in testing than a standard-height unit (up to 5,000 rpm).

We also tested a wide range of exhaust headers. TPIS manufactures several excellent long-tube designs that we felt would work well in the Challenge competition, including their late-model Pontiac GTO and Cadillac CTS-V offerings in stainless steel. Previous testing had shown them to be great performers over a wide rpm range, but a check into the EMC rules showed the previous callout for a chassis assignment for the headers was no longer required. This opened the door to other designs, and we acquired a couple sets of headers from American Racing Headers to test. This proved to be a good move, as we found power in American Racing's 1.750-inch/1.825-inch stepped diameter, 26-inch-long primary pipe Corvette headers with 18-inch-long collectors.

Our reciprocating assembly choices were twofold. We ordered up a flyweight (40.3-pound) custom crank from Callies to minimize reciprocating mass, and hoped that this crank (teamed with lightweight Manley forged rods and custom-crafted 459g CP pistons incorporating ultrathin .032-inch-thick Total Seal top and second rings) would deliver more power than heavier, more readily available parts. It's certainly proven to make a difference in the acceleration rates of competition cars that have powerplants so equipped. But these parts would require waiting while they were being crafted, so we went with more pedestrian parts to complete the testing. We'd go through the rebuild once again just before the Challenge competition, and drop our flyweight "jewelry" into the crankcase at that time. Since the basic dimensions (crankshaft stroke, connecting rod length, piston pin height) would remain identical, this was a solid plan and we'd be able to see the benefit of the lighter parts in back-to-back testing.

Additionally, this final pre-Challenge rebuild would give us the benefit of inspecting all of the engine's internals to ensure all was up to snuff right before the competition. Once accomplished, everything was found to be just fine. The only work done (besides the previously mentioned reciprocating assembly swap) was a tiny touch on the valve seats. They didn't really need it, but as Myron says, "After 600 dyno pulls, I had to touch the valve seats. It was just for insurance, so I could sleep knowing they were as good as they could be." No other changes were made to the heads.

"We should have just made an oil pan," Cottrell says. "The truck pan we used has a deep sump, but the front of the pan is quite close to the crankshaft. I think that might have been an issue, and some clearance there may have helped a little." As it was, using the stock pan and stock pickup with oil pressure limited to 45 psi, there were no lubrication issues after hundreds of 7,000-rpm pulls. The setup works reliably, but there may be more power on the table here. The engine was broken-in using Gibbs Break-in Oil, which proved to work extremely well compared to typical parts store oil typically employed for this purpose.

The maximum effort called for by the Engine Masters Challenge forced our crew of experienced performance engine specialists to go back to basics and put what we knew to the test. We learned a lot from start to finish, as the in-house dyno served as our guide while the other competitors gave us inspiration and direction to push the limits even further. Such an engine could serve as a phenomenal street or track engine, with ample power on tap throughout the sub 7,000-rpm range on pump gasoline.

Based on what was learned, TPIS will be offering several LS-based combinations capable of producing broad-based power on low-octane pump gas. These, too, will evolve, like the Challenge entry engine itself, but durability and reliability will remain priority one. With the LS design as a foundation, the future of pump-gas powerplants from TPIS is bright. When the dust settled, the diminutive 383-cube LS bullet belted out 629 peak horsepower at 7,000 rpm-that's well into big-block territory. It's also a warning shot across the bow that TPIS is a player in the wonderful world of LS power.