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High Performance Diesel Engines

By Bruce Mallinson

March, 2019

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Be careful squeezing the nickel when it comes to preventative maintenance on the truck that makes your living possible and supplies your family with a car, food, and a roof over their heads. What is the most important item in your life? This torsional damper which we removed from an ISX has 680,000 miles on it. The silicone fluid has been hard for quite some time negating the purpose of the damper, to remove torsional vibrations. The following is a list of what fails when the torsional damper has outlived its useful life: broken crankshafts, broken camshafts, broken alternator brackets, broken AC compressor brackets, broken flywheel bolts, broken flywheel housing bolts, knocking the springs out of the clutch disc, broken input shaft of the transmission, worn out U-joints and carrier bearing. I want you to think about this Kenworth with the destroyed torsional damper. We are replacing the damper, installing the mercury filled engine balancer and the timing case cover. But what else is about to fail? This truck could turn out to be a mechanical disaster. It would be interesting to follow the failures of this truck for the next 5 years. Think about the word “LEMON”, how many times have you heard someone say their truck is a LEMON. Was it? Or were the problems created because of a faulty torsional damper. Something else to think about, the person assembling this engine at the factory could have dropped this damper thus putting a dent into the outer cover and rendering the damper useless. Maybe it was dropped at the damper manufacturing facility or during transit. If your engine isn’t running smooth, don’t ignore the problem, it will only manifest into greater problems.

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Our dyno is our best diagnostic tool when it comes those hard to find issues. We recently had a customer visit us because his CAT 6NZ was bucking, sputtering, hesitating, and generally running rough. When we ran it on the dyno, we found this was no stock 6NZ, but a fully built motor with a performance cam and marine injectors. It put down 840 HP and 2500 TQ on the first pull all while running rough. Once we reviewed the data, the source of the problem became clear. Fuel pressure was dropping from about 90psi to 30psi from before the cylinder head to after the cylinder head. With a sight glass in the fuel line, we verified there was air in the fuel. After some more digging, we found the primary air filter housing was cracked letting air in the fuel. As for the lack of fuel pressure and/or volume, it had stock fuel lines and fuel pump and it seemed those marine injectors demand more fuel volume/pressure than what is standard for a 6nz. The customer opted to make the repairs himself. For experimental purposes we put a FASS system on that increased fuel pressure and reduced air in the system. The result was 870 WHP and 2600 WTQ which means this 6NZ was making 1,000 flywheel HP (accounting for 15% drivetrain loss). We encourage owner operators to save money by learning to repair their own trucks, but if you get stuck with a problem you just can’t figure out bring your truck in. We’ll help you figure it out and put you back on track. 

Fuel mileage, cruise control

Do you drive your truck, or does it drive you? We all love cruise control; however, it’s best used in automobiles, empty pickup trucks, and motorcycles. Anything pulling a trailer should very seldom use cruise control unless you are on dead level terrain or slight downhill. If you listen to our radio show with Kevin Rutherford (The Power Hour, on Tuesdays from noon to 2 pm EST), all the owner operators that call in and complain about poor fuel mileage do not have a turbo boost gauge or do not know what it means. My first question is always, “how much boost do you use when driving on the level and the wind is not blowing.” Many times, the answer is, “this is an old fleet truck and it didn’t come with a boost gauge.” My friends, the boost gauge kit is $68.00 and is very easy to install, in fact you can install it in your driveway or truck stop parking lot. If they have the boost gauge the answer is usually around 18 psi on the level. My fellow trucking friends, there is NO fuel mileage at 18 or more psi of boost on the level. There could be many reasons why it is taking all that boost to move the rig at the speed you have chosen. First, try slowing down 5 mph and see if the turbo boost drops 5 psi or more. Here is a list of other possibilities: the turbocharger on the engine could be too small creating too much back pressure, the mufflers could be clogged or too restrictive, the tires have high rolling resistance, the gap between the trailer and cab is too far (air can only jump 36 inches at highway speed), the load is pulling hard or the trailer is loaded wrong, the exhaust manifold is stock and will not allow the exhaust to escape from the engine, the truck is geared wrong, a bad ECM program, or you are NOT paying attention to the boost gauge and using cruise control and the terrain is rolling. I feel driving is 66% of fuel mileage. Recently I had an owner-operator call and could not drive his DDEC5 under 18 psi of boost on the level, he was from Minnesota and never gets East so I could not see the truck. We have long conversations and I realized someone installed a 12.7 turbo on his 14-liter engine. I shipped him the performance turbo we use on a 14-liter Detroit and with the same load and speed, his boost went from 18 psi to 8 psi. That was a gain of 1.25 mpg, less exhaust gas temperature, and a more free running truck. If your engine has EGR and equipped with a Variable Geometry (VG) Turbocharger, the variable geometry section of the turbine housing may not be opening properly, soon enough or not enough. All three symptoms will lower the fuel mileage, cause the truck to drag, and increase the exhaust gas temperature. Our engineering department can design an ECM program for your engine and your driving conditions. As you can see, many items determine fuel mileage, it’s up to YOU to make the changes to your truck and your driving style to improve your fuel mileage. 

Written by: Bruce Mallinson and Andrew Wilson,

Pittsburgh Power Inc.,

3600 S. Noah Dr. Saxonburg, Pa. 16056

Phone 724-360-4080