High Performance Diesel Engines

Bruce Mallinson, Peter Sharp, Leroy Pershing
September 2023

I always wondered why Kenworth never made the cab of their great trucks about 6" longer so taller people would have room for their legs. Recently I had the opportunity to meet Mike McWilliams from Bakersfield, Ca. He is now 56 years old, and in his younger years, he was a welder fabricator in the oilfield. The lure of the open road, being self-employed and heavy hauling led him to purchase a 1979 A model Kenworth. I asked him what made him do the things he does to equipment, and he said, "It's in my blood; I can't leave things alone. I always have to improve the design, like making my old W90A a 6" extended cab. I also extended the frame horns 9" to make it a long nose. I couldn't find the long hood, so I made a 9" cowl and kept the short standard hood." After California banned the use of non-emission trucks, he decided to pull his 5th-wheel camper trailer with the Q model. To get traction, he built a tilt tray that latched into the fifth wheel plate. That was the only securement, just the kingpin and the weight of the D-4 dozer to hold it down. He could not pull the traveling tailor without the D4 on the deck, or the tray would lean back to the ground.

Next month we will showcase his newer Kenworth with a 180-inch bunk and a box on the front of the trailer that hauls his dune buggy or Harley Davidson. 

It has been 30 years since the last N-14 mechanical engine rolled off the assembly line. The mechanical N-14, in my opinion, is an excellent engine that is often overlooked by the younger generation of drivers and sometimes even older ones.

We recently finished rebuilding one of these engines in our shop on a 1652 CPL that was making 430HP from the factory. We installed steel pistons to replace the less durable aluminum stock pistons, a larger turbo with custom flow injectors, and a newly rebuilt fuel pump. With this setup, we are able to take this engine from 430 flywheel horsepower to 625 flywheel horsepower and still be reliable on the road.

If you, too, have an older N-14 or Big Cam Cummins engine and are looking to increase its horsepower and torque, please give us a call. We are one of the few shops in the country that still regularly stock parts for this engine as well as a large inventory of miscellaneous parts in the clearance section of our website.

If you listen to our podcasts with Kevin Rutherford or our radio program on Sirius XM, you may have heard us talk about piston side thrust. I have received a few questions asking to explain that in a bit more detail. The funny thing about most engine topics is that the rabbit hole is deep and simple ideas can become complex quickly. I will attempt to explain what I am talking about plainly. So, we start with visualizing the engine from the front of the truck. The engine turns in the clockwise direction. SEE PHOTO. So you can see in the photo the major portion of the thrust is exerted on the left side of the cylinder. Naturally, this is called the major thrust side and the right side is called the minor thrust side. The amount of pressure on the liner is dictated by crank angle, cylinder pressure, piston speed, acceleration, and connecting rod geometry. A real world application is how one engine can have a shorter connecting rod than another. The one with the shorter rod would have more side thrust or friction. Friction in an engine is converted into heat. A typical symptom of high piston to liner friction is high oil or coolant temperature. Excessive friction will but more heat into the piston which will heat the oil via the oil squirters trying to cool the piston or the liner will absorb the heat and put that energy into the coolant. A poorly tuned engine with too much timing advance will add increased cylinder pressure. This excessive cylinder pressure will translate into increase side thrust which will increase friction. Again, this will show itself in high oil or coolant temperature. The most intuitive way to think of it is how lower piston speed makes less friction. Put your hands together and rub them as if you were trying to warm your hands. The faster you do this, the more heat you’ll generate. The harder you push your hands together the more heat you generate. Do both and you will quickly feel how excessive friction can lead to excessive heat in your engine. There is not much you can do as a consumer to change this issue since the side thrust is designed into the engine. There are a few things to consider or watch out for. Your engine oil is what reduces the piston to liner friction. Having proper oil type, capacity, and clean oil make all the difference. When that oil is not there or has broken down, your engine will destroy itself from the generated heat. You’ll see this in scored liners, broken pistons, etc.

Written by: Bruce Mallinson, Peter Sharp, Leroy Pershing - Pittsburgh Power Inc., 3600 S. Noah Drive, Saxonburg, PA, 16056  Phone (724) 360-4080, Email: [email protected]