We all have heard of the phases “an engine is essentially a giant air pump” and "more air in and more air out equals more horsepower”. What is not clearly understood is that there is a limit to how much air an engine can digest. We can’t force more air into an engine, no matter how big the air intake system is, if the engine does not want it. Engine air requirements are determined by the following: engine size (displacement), RPM at maximum horsepower, maximum boost pressure, and engine volumetric efficiency. The graph below shows the air flow needs for our 5.9 Cummins.
The above graph assumes a typical volumetric efficiency (VE) for the stock Cummins engine. Changes to a better air intake system, larger intercooler, camshaft and turbocharger or ported head will improve the VE up to 10% above the CFM values shown. A stock '04 Cummins engine is set at the factory at 22 psi boost with the maximum horsepower occurring at 2900 rpm. From the above graph, the amount of air needed by this engine is 640 CFM. If the boost is increased or the engine rpm at maximum horsepower is raised, the engine's air requirement will be increased.
The Dodge/Cummins stock air box and air filter is larger than the Duramax and Power Stroke and consequently Dodge has the least restricted stock air inlet system of the Big Three. PSM real-world and dyno testing has shown that the most restricted part of the Dodge air box is the air inlet area into the box. Dodge must have realized this limitation as they increased the inlet area into this box from 19 square inches to 26 during the '04.5 model change. Even this larger area is insufficient to feed the air box all the air the engine requires. We have solve this problem by providing additional air inlet area at the bottom of the stock air box by using a 4-inch diameter duct that provides 12-1/2-square inches more area for increased air flow into the air box. The PSM cold air intake system will provide sufficient quantity of air to the Cummins engine to produce 450 rear wheel horsepower.
The stock air filter is adequately sized for the stock air box. However, our testing has shown if we add additional air to the box using the PSM cold air intake kit, the filter now becomes the limiting factor in delivering all the air the Cummins engine needs for maximum performance. A small gain in performance can be obtained by changing the stock air filter to a high performance filter.
To maintain the maximum performance from the engine, the density of the air entering the air intake system is very important. PSM real-world testing showed that horsepower gains from most aftermarket air intake systems that increased air intake flow can be totally negated if underhood air heated by the engine is getting into the air box. In fact, when this situation occurs, our testing has shown the engine will produce less horsepower than an engine using the stock unmodified air box. Most aftermarket air intake manufactures appear not to understand nor consider the total effects of underhood heated engine air getting into their air boxes. Most aftermarket air boxes are designed to shield hot air from the air box, but does not prevent hot air from entering the air box. Our testing has shown that the stock Dodge “sealed” air box design is the best air box for preventing hot underhood heat from entering the air intake tube. The following graph shows these temperatures during a 4-mile 6% grade climb.
From the graph you can see that underhood air can exceed 150 degrees. The air intake temperature for the "shield" type air box follows the rise and fall of the underhood air temperature because a "shield" air box obtains 45-50% of the air from under the hood. The stock air box is "sealed" and obtains air between the inner and outer right front fender where the air is much cooler and isolated from the heated underhood air. The PSM cold air intake kit provides additional cold air from behind and below the front bumper to the stock air box thus lowering the intake air temperature an average of 2.5 degrees below the stock system or 32 to 44 degrees below a typical "shield" type air box.
When using a "shield" type air box, underhood air temperature is self-perpetuating; hot underhood air results in hotter intake air, resulting in higher EGTs, causing underhood air temperature to increase, resulting in this cycle being repeated until you back off on the throttle as shown the 3.5 mile point on the graph.
Why is keeping hot air out of the air intake system so important? Air is made up of molecules. Molecules that get hot expand and become larger than cool air molecules. Fewer hot air molecules can be packed into a given volume (say a 1-foot cube) compared to the number of smaller cool air molecules. The greater number of air molecules that can be placed in 1-cubic foot box, the heavier the box becomes. The heavier the box is, the denser the air is inside that box. The more air molecules the engine digests in a cubic foot of air the more power an engine will make. Therefore, to maximize the power of your engine, you should use an air intake system that provides cold air to the engine under all driving conditions. Engines typically produce 5% more horsepower for every 30 degrees of cooler intake air. A PSM cold air intake system is one of the very few systems available that can deliver a continuous supply of cold air to the engine for maximum performance.
With the Electronic Control Module (ECM) in our ‘03 and newer common-rail trucks, fueling adjustments are continuously made while the engine is running. There are two sensors (1 on the engine which is called the manifold absolute pressure (MAP) and the other on the air intake duct) that measures air temperature and air pressure. The MAP sensor sends continuous data to the ECM which calculates air density and makes adjustments to the fuel injector flow. When air intake temperature is increasing, the MAP sensor sends a signal to the ECM which in turns reduces the time the fuel injectors are turned on. This reduces the amount of fuel injected into the combustion chamber. Less fuel injected means less power is being produced. The exhaust gas temperatures will also go down since the heat produced during combustion is less.
To summarize, air flow and air density have major influence in the overall performance of an engine. Aftermarket published air flow numbers that are greater than the engine’s requirements do not produce additional horsepower. Providing cold air to the engine under all driving conditions will guarantee the maximum horsepower and torque from your diesel engine. PSM has performed the dyno and real-world testing and strongly believes they have designed the best and lowest cost cold air intake system for the ‘03 and newer Dodge/Cummins turbo diesel trucks for heavy towing and hauling applications.
