The Duramax L5P Goes Back Together
In the May 2017 issue of Diesel Power, in an article titled “Inside the Duramax L5P,” we visited Gale Banks Engineering in Azusa, California, and documented the complete dismantling of a straight-out-of-the-crate version of GM’s latest 6.6L powerplant. After the engine was completely taken apart, its individual components were compared side by side with the equivalent internal pieces of a Duramax LML. The comparison allowed us to see the innovations and changes GM integrated into its new diesel creation, and many of the features show there’s potential yet to be unlocked.
Not long after returning from our visit, we received a call from Gale Banks, who told us about his plan to put the same L5P back together. He explained that the reassembly process would include measuring tolerances and clearances of key pieces. Recording this data would also provide an accurate analysis of the engine that can be used to design such performance components as camshafts and pistons. It also provides insight into possible issues that may arise from modifying an L5P. Any time there is a chance to gain more understanding of what makes this new engine tick, count us in.
A few weeks after our phone conversation with Gale, we spent three days with Gale Banks Engineering’s lead engine builder, Mike Keegan, as he reassembled and measured the L5P’s critical internal components.
The bearing caps are installed on the block and torqued to specifications so the bore can be accurately measured.
The camshaft’s journals (2.3995 inches), lobes, and cam bearings (installed in the block) are analyzed next. After recording the measurements, Mike smears the cam bearings and shaft with assembly lube before installing the cam in the block.
Assembly lube is applied to the crankshaft’s bearings and journals before the crank is set into the block. Bearing-cap main bolts are torque-to-yield (the fastener is designed to yield/stretch when torqued), which causes it to deform and become permanently elongated, so new bolts must be used for final assembly.
Silicone is applied to the original side bearing cap bolts before they are installed. Once they are installed, all the cap bolts are torqued to specification. After the bolts are secured, Mike checks the crank thrust clearance.
Mike measures a piston’s wristpin bore, wristpin, and rod bearings before mating the pistons to the connecting rods. This provides the measurements used to determine the clearances between components. Our L5P’s wristpin-to-piston clearance is 0.0008 inch.
All the pistons and cylinders are measured to check tolerances. The piston diameter is 4.0521 inches and cylinder bores are 4.0551 inches, which creates a clearance of 0.003 inches. The bores have a straightness taper of 0.0003 inches and are 0.0002 inches out of round. Rod bearings are coated in assembly lube before the pistons and rods are installed.
Mike begins assembling the front of the L5P, installing the oil-pump drive gear, oil pump, high-pressure fuel pump, and timing cover.
What Are the Limits of a Stock 6.6L Duramax L5P Engine?Tearing an engine apart and putting it back together can yield a lot of information about that powerplant, including how well or how poorly it is constructed. However, disassembly and rebuilding does not provide all the facts about what the engine can do. The only way to truly understand everything is to test it. And the best place to test an oil-burner is in the controlled environment of a dyno cell.
Shortly after Gale Banks Engineering’s lead engine builder Mike Keegan finished reassembling the 6.6L Duramax L5P engine, the powerplant was mounted on the dyno (minus the EGR and catalytic converter, in order to see how the engine performs without those restrictions), ready to be put through its paces.
One problem with the engine not having an EGR is that all the exhaust gases go directly into the turbocharger. The excess exhaust volume is more than the turbo is designed to support, which hinders its ability and efficiency.
On the dyno, a Banks ECU is used to control engines that are being tested, making easy fuel and timing adjustments possible for our L5P test. Sensors were installed to monitor every pressure, temperature, density, and bit of data that can be analyzed. All the information was tied to two prototype Banks Power iDash gauges that act as data loggers.
For the first test, which we used as a baseline, the engine was run at 2,800 rpm. It produced 450 hp and 844 lb-ft of torque (peak torque is at 1,600 rpm) and put out lots of vital ancillary information. Additional tests were then performed, with minor adjustments made to timing, fuel, and the position of the turbo’s vanes in order to determine the engine’s maximum potential. With the turbo vanes wide open, fuel delivery increased (to the upper limit of the stock system), and timing set to a sweet spot (advanced until an increase in performance was seen), our L5P made 540 hp and 915 lb-ft of torque at 3,100 rpm—the limit for the turbocharger (it got too hot due to an overabundance of exhaust-drive pressure), as well as the fuel system.
The dyno gives us an abundance of information about the stock L5P’s performance potential and its limits. Capturing this type of data can be a huge benefit to engine builders and aftermarket-parts manufacturers who are working to resolve the engine’s shortcomings and push its performance limits farther.
A look inside Banks Power Dyno Cell 2 and the 6.6L Duramax L5P engine that is ready to run.
Gale Banks EngineeringAzusa, CA 91702