Issue link: http://read.uberflip.com/i/588723
72 DIESELTECHMAG.COM DIESEL TECH NOVEMBER 2015 155555BacBum13h.indd 1 9/9/15 4:28 PM TECH CORNER B Y Robin Ridgeway TECH CORNER B Y TECH CORNER B Y TECH TECH TECH CORNER B Y Are You Feeling Me? How to eliminate pressure surge S Strictly Diesel, an online and in-shop marketer of diesel parts and service located in Phoenix, Ariz., is one of several manufacturers of ported-shroud compressor housings for stock turbochargers found in 1999.5 and up Ford Super Duty 7.3L Navistar diesel engines. The ported compressor housing is one of several possible solutions to a turbo perfor- mance issue called "compressor surge" found in 7.3L Power Strokes that are performance modified, but also found in stock configurations when the engine is under significant load. Compressor surge can be extremely destructive to the turbo by damaging the thrust bearings and potentially even mechani- cally damaging the compressor wheel itself. The turbocharger on a diesel engine utilizes the energy from the exhaust gases to drive a turbine-powered centrifugal air compressor that increases the density of the air entering the combustion cham- ber. The turbocharger allows for increased fuel economy and power, and improves the combustion efficiency of the engine. Operating Range Before discussing surge in the compressor of the turbo- charger, it is important to understand what the designed operating range of the turbo is intended to be. Each turbo- charger compressor has its own unique performance finger- print. This fingerprint is shown graphically on a diagram called a compressor map. The map consists of a pressure ratio on the Y axis (compressor outlet pressure/compressor inlet pres- sure) with the mass flow of the turbocharger shown on the X axis, usually in units of pounds-air-per-minute. The data used to produce a compressor map is collected by running a turbo on a properly instrumented test stand in a test chamber while running the turbocharger at a constant speed and then vary- ing the pressure ratio for that speed.