Last month, we began a simple buildup of an all-aluminum 5.3L Gen III engine that was a brand-new production overrun aluminum-block 5.3L SSR truck engine. This SSR engine is virtually a clone for the popular iron block LM7 GM truck engine, with the exception of the aluminum block. Last month, on Lingenfelter Performance Engineering's (LPE) Digalog Testmate dyno with little more than a swap to a bigger camshaft and a set of headers, we made an amazing 413 hp, which equated to a 100 hp peak-to-peak increase. But we weren't finished yet.
LPE's Project Director Jason Haines, along with expertise from "Dyno Bob" VanderHart, decided to really put the screws to our little 325ci small-block by adding some larger injectors, as well as a set of LPE's CNC-ported heads, a swap to one of Comp Cams' FAST LSX intake manifolds, along with a couple other little goodies to see if we could make this little motor sing. We'll cut right to the finish and tell you that Little Bro managed a respectable 458 hp at 6,800 rpm and 392 lb-ft of torque at 5,800 rpm.
Up To SpeedLast month we added a pretty healthy LPE-spec'd hydraulic roller cam (the details are in the Cam Box). Dyno Bob noticed that the stock fuel injectors were maxing out at 100 percent duty cycle. What we really needed was larger injectors. The stock injectors are rated at 25.4 lb/hr of fuel, which is good for between 350 and 400 hp at roughly 85 percent duty cycle with the fuel pressure at 58 psi. When you exceed 85 percent duty cycle in search of more fuel, it's time to increase the size of the fuel injectors. The next step up in the Delphi injectors is 30.2 lb/hr, good to between 400 and 475 hp, which is what we put in our 5.3L engine. It's important to note that the factory runs the 4.8 and 5.3L truck engines at a significantly richer air/fuel ratio than the passenger-car engines. According to Haines, the factory calibration for the truck engines can run as rich as 11.5:1 at wide-open throttle (WOT), to protect the exhaust valves and the catalytic converter. Our baseline testing revealed that our 5.3L engine was running around 12.2:1 air/fuel ratio.
With the larger camshaft and now with larger injectors, LPE had to go into the factory computer to rescale the fuel map to set up the proper fuel delivery curve. For these first runs, LPE had been using production ignition and fuel curves. For calibration changes, LPE uses proprietary in-house software. LS1 Edit, HP Tuner, and others offer that capability, but it's beyond the scope of this story to get into the details on specifically how that was accomplished. The LS1 Edit program is available to any enthusiast, but it does demand significant knowledge of both engine tuning and how to navigate through the complex GM computer using this software. This is not for beginners, but the software does allow tremendous latitude for spark and fuel tuning to get the most out of the changes made to the engine.
Heads UpUp until now, our changes had been relatively inexpensive with a camshaft, headers, injectors, and valvesprings. We'd added an amazing 100 hp to the stock baseline, and we were most impressed with the stock truck intake. At 413 hp, we were still using an unmolested stock truck intake manifold along with the stock 75mm throttle-body. Before we changed the intake, we decided to test a set of LPE's CNC-ported heads with the truck intake to see how well this intake would perform.