Think carefully about restriction when you modify an air intake. Allen Wright, manager of advanced engineering for ArvinMeritor, warned attendees at the Association of Equipment Maintenance Professionals' 2003 Management Conference that a high-restriction system requires more frequent service, it can sap performance, and slash engine life. He explained how common choices choke engines by comparing three intake systems he's seen on scrapers with identical Cat 3412TA engines.
The good choice employed an 18-inch-diameter air cleaner with built-in precleaner, dust ejector, and an inner safety filter. The cleaner produces 6 inches of restriction. The rain hat and the reducer at the turbocharger inlet are the only other major restrictions.
Wright says the bad option is a 15-inch-diameter air cleaner without a built-in precleaner or safety filter. The air cleaner alone produces 7½ inches of restriction, compared to 6 inches with the good air cleaner.
"This unit is designed primarily for on-highway trucks, and it comes chrome plated," Wright says.
The matching chrome rain hat is more restrictive, too.
This one uses the same style filter as the bad system, but adds an aftermarket precleaner that creates 8.5 inches of restriction. The mounting location changed, and the buyer tried to save money with a reducing elbow at the housing outlet and smaller tubing throughout. That choice alone tripled restriction downstream from the housing, compared to the good arrangement.
"This system is downright ugly because it only leaves a little more than 2½ inches of restriction to accommodate dirt buildup on the filter before the cartridge should be replaced (according to the manufacturer's service recommendations)," Wright says. "That guy's either going to replace a lot of filters or over-fuel the engine."
Wright remembers a contractor who bought a machine and retrofit it with a different engine. The replacement required more air than standard, but the intake system never changed. The operator ignored black smoke pouring from the exhaust stack between service intervals.
"The owner rebuilt that engine twice one year," Wright says. "It's a good reason to use filter-restriction indicators, and to watch how you spec intake systems."