Usage:
All 3116, 3126, 3208, 3306, 3176, C-10, C-12, And 3406 Truck Engines
If not currently equipped with an Exhaust Backpressure Tap, install a pressure tap on a straight length of exhaust pipe. This tap should be located as close as possible to the turbocharger or exhaust manifold on a naturally aspirated engine, but at least 305 mm (12 in) down stream of a bend. If an uninterrupted straight length of at least 457 mm (18 in) is not available, [305 mm (12 in) preceding and 152 mm (6 in) following the tap), take care to locate the pressure probe as close as possible to the neutral axis of the exhaust gas flow. For example, a measurement taken on the outside of a 90 degree bend at the pipe surface will be higher than a similar measurement taken on the inside of the bend.
The pressure tap can be made by using an 1/8inch NPT half coupling welded or brazed to the desired location on the exhaust pipe. After the half coupling is attached, drill a 3 mm (.12 in) diameter hole through the exhaust pipe wall. If possible, remove burrs on the inside of the exhaust pipe so that the gas flow is not disturbed. The gauge or gauge hose can then be attached to the half coupling.
Exhaust backpressure is measured as the engine is operating at rated conditions. Either a water manometer or a gauge measuring inches of water can be used.
Do not use the tapped hole in the exhaust pipe elbow, directly downstream of the turbocharger, because this tapped hole is for the temperature measuring pyrometer only. The use of this tapped hole for exhaust backpressre readings may lead in erroneous readings.