High Performance Diesel Engines

Bruce Mallinson and Leroy Pershing
February 2024

Years ago, when the Big Cam Cummins engine was in 74% of all trucks sold in North America, we at Pittsburgh Power developed 42 items to improve the power, longevity, and fuel mileage of this wonderful engine. We really knew this engine well and still do, then one morning a well-dressed man named Al Puhlman walked into my office with one of my magazine articles and asked me if I was the writer. My answer was yes. He proceeded to tell me he had a Big  Cam 3 in a Crown bus that he converted into a motorhome, and the engine laid on its side halfway back in the bus under the floor. I leaned back in my chair and looked at him,  thought to myself, I have heard a lot of stories, but this one takes the cake! Like I said, he was a good-looking, well-dressed, and well-spoken man, so I said when can I see this motor home? His reply was tomorrow. It’s parked at a campsite in Washington Pa right now. Now this was back around 1996. The next morning, it was in my parking lot, an absolutely gorgeous motorhome; the side compartment was open, and there was the Big Cam Cummins engine with chrome valve covers lying on its side. I just stared at it, wondering how the oil pan and oil pump supply oil to the engine. I thought this was impossible, so I got a creeper, slid under the motorhome, and saw the strangest-looking oil pan I have ever seen.

The engine actually was on a 3-degree rise from being completely horizontal, enough to allow the oil to return to the pan. That day, a wonderful friendship began. He wanted a lot of horsepower, and I was the one that made his dream come true. This Crown motorhome started life as a Crown mobile post office powered with an NH 220 Cummins engine. Al and his son converted this traveling post office to a stunning motorhome and installed the Big Cam Cummins engine under the floor. This motorhome has 34 gauges, 17 hides of leather, a 36” television that comes up out of an end table, and the list goes on. The horsepower is around 700, we did not have a dyno at the time to verify the power. Al Puhlman was raised in Western Pennsylvania, and in 1962, his family moved to southern California; this motorhome is now in Round Mountain, California, near Redding, California. 

In 2023, a customer brought us another Big Cam Cummins engine to go into a 1938 Harlan bus to set the land speed record at Bonneville Salt Flats. The following pictures are of the engine during the build process, so it has not been painted at this time. Please note the exhaust manifold, oil pan, and mercury-filled engine balancer behind the new torsional damper. The engine is around 750 to 800 horsepower and will be situated in the bus with the intake manifold facing the ground. You can see how the oil pan sump will be facing the ground.     


EGR was introduced to the trucking world and has been with us for over 20 years. The introduction of hardware that lowered emissions reshaped the industry, and emissions regulations continue to shape our world. From a repair shop perspective, our world went from rebuilds, injectors, and pumps to EGR coolers, DPF cleaning, and DEF diagnostics. The technicians of today live in a different reality than years ago. Hearing an engine roar to life after a new pump and injectors was satisfying. A technician’s job now is borderline ‘nerdy’ with all of the computers and wiring involved. So, back to EGR, why did the OEMs use that technology, and how does EGR reduce NOx?

For starters, DEF and SCR are the superior technologies, but they weren’t ready for mass production in 2003 when EGR came out. EGR is one of the simple and effective ways to reduce the NOx coming out of the engine. The biggest reason EGR is so effective is that it decreases the peak temperature of the combustion flame. It does this through the dilution effect, a thermal effect, and an added mass effect. The dilution effect is a fancy term, which is what it sounds like. The gulp of air that the cylinder takes in is diluted with EGR. The combustion flame has to try harder to find oxygen in the cylinder to burn with. The less oxygen there is, the more ‘left-over’ fuel molecules there are, and soot forms more easily. The “added mass effect” and “thermal effect” work with the dilution effect. When you dilute the intake with something other than burnable oxygen, that something absorbs or takes heat away from combustion. When combustion happens, there is a large release of heat. That heat and pressure is what pushes the piston down. Not all that heat goes into pushing the piston down. It is distributed to the block, pistons, and exhaust, to name a few. The block, pistons, and exhaust absorb heat. Hence, engines get hot. EGR in the cylinder takes heat away and reduces the amount of push on the piston. This is one of the reasons why EGR hurts power and fuel mileage. These three effects reduce cylinder temperature, which reduces NOx formation. Since NOx needs heat and pressure, reducing those components makes it harder to form.

There are many downsides to utilizing EGR, and the ECM tries its best to manage how much it puts in. OEMs know the downside and only put in what they have to. That is why, in some ways, the introduction of DEF and SCR has been a blessing. Using those technologies means the engine has to eat less of its own…waste. One major issue with using EGR is in the design itself. Most OEMs use a high-pressure EGR system. This system works off the fundamental physics property that pressure will always try to equalize. So, areas of high pressure will flow to areas of low pressure. In the case of an EGR system, the turbocharger generates high pressure in the exhaust manifold, so it will flow into the intake manifold. The more boost your engine makes, the higher the exhaust back pressure to drive EGR into the intake. High exhaust backpressure leads to less performance and fuel mileage; this is a known fact. The other downside we mentioned earlier is the decrease in combustion performance. This decrease in combustion performance also comes with increased particulate matter emissions or soot. Displacing oxygen in the cylinder for exhaust gas, which doesn’t burn with diesel, leads to rich pockets in the cylinder. These rich pockets contain unburned fuel and, if not dealt with, will accumulate and grow into soot particles. The larger particles get trapped in sensors and your DPF. This is why whenever you have an EGR sensor acting up, it will lead to even more issues with soot buildup. Soot oxidation rate, the rate at which soot burns, is affected by EGR, especially in the later stages of combustion. This is where Max Mileage can help. By lowering the temperature at which the soot breaks down, Max Mileage will make soot easier to burn in those later stages. Undoing some of the harm that EGR causes.

Written by: Bruce Mallinson and Leroy Pershing, Pittsburgh Power, Inc., 3600 S. Noah Drive, Saxonburg, PA, 16056 Phone (724) 360-4080; Email: [email protected]; Website: www.PittsburghPower.com