Better Roads Digital Magazine
Issue link: http://read.dmtmag.com/i/221550
choose, the eﬀect of extra airﬂow diﬀers between gasoline and diesel engines. Since gasoline engines are "air throttled" (fuel is mixed proportionally with airﬂow, ideally at an air/fuel ratio of 12.5:1), power output is directly related to total airﬂow. In a practical sense, that means a gasoline engine with enhanced airﬂow can make the same power at a lesser throttle opening, consuming less fuel per mile. Conversely, the engine has more power for accelerating, climbing grades or hauling/towing. In contrast, diesel engines have no air throttle: Diesels are "fuel throttled," in that power output is determined by how much fuel is injected, which can range from a 50:1 air/fuel ratio at idle to about 22:1 at full power. A turbodiesel can ingest as much air as the turbo can supply for the engine load. As on a gasoline engine, airﬂow enhancements on a diesel improve eﬃciency. COOL AIR BENEFITS The location of the air intake is another factory to consider. Some intakes are designed to capture cooler air from the outside of the engine bay, instead from under the hood. The latter area typically heats the air by as Aftermarket "cold-air" intake systems are designed for direct replacement of OEM air box and intake tube. much as 50 degrees when passing through the radiator and air conditioning condenser. What's the advantage of not drawing in heated, underhood air? Cooler air is denser, containing more oxygen. The more oxygen that ﬂows, the more fuel that can be burned for more power. Another way to lower the temperature of intake air is with a charge-air cooler, also called an intercooler. On a turbodiesel, intercoolers can be either an air-to-air or air-toliquid type. Both work well, but the liquid type requires an additional air/heat exchanger. EXCEED THE DISTANCE. The idea behind aftermarket intakes is to get as much cooler air from the outside as possible into the engine. As a general rule of thumb, for every 10 percent reduction in charge-air temperature, you can expect a one-percent or more increase in air density and power. That might not sound like a lot, but it can add up, and charge-air cooling not only increases power, but also prevents detonation (uncontrolled combustion of the air/fuel mixture that causes excessive temperature and pressure in the cylinder, and engine damage as well). Intercooling has additional beneﬁts for diesel engines in particular. It not only increases the charge-air density, but also lowers exhaust-gas temps (EGT). Keeping that number below 1,300 degrees is critical for ensuring long engine life. Lowering the intake temp usually results in an almost equal reduction in the EGT. FORCED AIR 1-800-442-0056 (530) 893-5209 PROUDLY MADE IN THE USA Text INFO to 205-289-3781 or visit www.ppmrequest.com 12 PROPICKUP December 2013 Another key factor is air pressure. On a naturally aspirated engine, it's limited to atmospheric pressure of 14.7 pounds per square inch at sea level (which is why engine power drops when you drive at higher altitudes with thinner air). On the other hand, ram-air intakes that scoop up outside air improve performance as vehicle speed increases, resulting in a natural form of forced induction. Turbos and superchargers do the same thing, but with far more force, as does nitrous oxide, an oxygen-rich gas that's a chemical form of forced induction. In sum, whether your work truck is gas or diesel, naturally aspirated or forced induction, the cooler the intake air, the better. And make sure to clean or replace the ﬁlter element regularly, whether it's a factory or high-ﬂow unit, especially when you're running your truck at a dusty worksite.