Usage:
793 (3SJ) Trucks
Reference: Service Magazine; August 22, 1994; Page 2; "Procedure To Modify 4P-4866 Coupling And 4P-4864 Housing To Work With New High Pressure Turbocharger".
Description of Change: This article replaces the article with the same title on Page 8 of the May 8, 1995 Service Magazine.
Several changes have recently been made to improve the service life of the turbocharger and the performance of the engine. Each new change has resulted in new components in the turbocharger group. The changes and their benefits are listed below.
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- * Change One upgraded the 48 trim high pressure turbocharger to a 56 trim. The new turbocharger increased the quantity of air to the engine, resulting in lower exhaust temperatures. Also, the wastegate orifice was increased in size. The size of the orifice varies from 33 to 38 mm (1.3 to 1.5 in) depending on the machines' operating altitude.
- * Change Two added a new low pressure turbocharger with a larger compressor wheel and housing. The larger compressor wheel allowed the turbocharger to pump the same volume of air, but at a lower speed. This speed reduction resulted in longer service life of the turbine wheel. The wastegate orifice was also changed to remain compatible with the new turbocharger.
- * Change Three added a new high pressure turbocharger. The turbocharger's turbine housing and center housing are now made from the same material. This reduced the exhaust leakage between the center housing and the turbine housing because both parts expand and contract at the same rate. Also the low pressure turbocharger changed to include a turbine wheel with lower stresses. This will result in a longer service life for the turbine wheel.
- * Change One upgraded the 48 trim high pressure turbocharger to a 56 trim. The new turbocharger increased the quantity of air to the engine, resulting in lower exhaust temperatures. Also, the wastegate orifice was increased in size. The size of the orifice varies from 33 to 38 mm (1.3 to 1.5 in) depending on the machines' operating altitude.
To maximize exhaust temperature reduction, all engines built to change level 0, as per the "Turbocharger Information Chart", should be updated to change level 1 or higher of the "793 Turbocharger Update Chart".
All engines can be updated to any higher version. Whenever updating the turbochargers on a 793 Engine, use only a turbocharger and wastegate orifice plate that is listed in one of the two options in the "793 Turbocharger Update Chart". Do NOT use any combination of turbochargers or wastegate orifice plate other than a combination that is listed in this chart. Failure to do so can cause excessive cylinder pressure or excessive exhaust temperature. Operating an engine with either condition can cause major engine problems.
Do NOT mix 48 and 56 trim high pressure turbochargers on the same engine. Acceptable 48 trim high pressure turbochargers are the 4P-4693 and 109-8925 Turbocharger Groups. Any 48 trim high pressure turbochargers can be mixed on the same engine. Acceptable 56 trim high pressure turbochargers are the 0R-6757, 0R-6966, 106-4557, and 121-3850 Turbocharger Groups. Any 56 trim high pressure turbochargers can be mixed on the same engine.
Do NOT mix low pressure 4P-4646 Turbocharger Groups with either low pressure 114-1980 or 122-0351 Turbocharger Groups on the same engine. But, the low pressure 114-1980 and 122-0351 Turbocharger Groups can be mixed on the same engine.
Adaptable To: All the turbocharger variations can be upgraded to the latest change. The new 122-0351 Low Pressure Turbocharger Group and the 121-3850 High Pressure Turbocharger Group are direct replacements for the former turbocharger groups if the other components are also updated. The 4P-4693, 106-4557, and 4P4646 High Pressure Turbocharger Groups have been canceled.
