Engine Upfit

The Final-Stage Parts That Finish a Conversion Right

Engine upfit is one of the most commonly overlooked parts of a conversion. Many customers assume that because they have a dressed donor engine, they can simply set it in the chassis and connect everything. That is rarely true.

Fan hubs, fan blades, accessory drives, intake manifolds, thermostat housings, oil pans, and power steering pumps are often engine and chassis specific. Using the wrong combination creates clearance problems, alignment issues, and custom fabrication that could have been avoided.

Key areas that typically need attention:

• Fan Hubs – These are engine, chassis, and model specific. The center height from the crankshaft to the fan hub must match the truck. A Peterbilt 389 requires approximately 15.75", while a Western Star 4900 needs around 20". The wrong hub leaves the fan blade off-center in the shroud.
• Fan Blades – Blade count, offset, bolt circle, and pilot diameter all matter. A Paccar engine uses a different pilot and bolt circle than a CAT C15, so the blades are not interchangeable. The wrong offset can cause contact with the engine or prevent the blade from engaging the shroud properly.
• Serpentine Belt Systems – The most common upgrade. Serpentine belts offer clear advantages over older V-belt setups, but they require matching brackets, idlers, and pulleys so everything stays in alignment. We still support V-belt configurations when needed.
• A/C System – Updating to current compressor and line fittings (at the compressor, expansion valve, and condenser) avoids the need for custom one-off lines later.
• Intake Manifold & Thermostat Housing – These vary by the original chassis the engine came from. A Detroit Series 60 that came out of a Freightliner has a different intake location and angle than one originally installed in a Peterbilt. Thermostat housings are also vertical or horizontal, which determines the correct upper radiator tube.
• Oil Pan Configuration – Front-sump vs rear-sump pans are dictated by the original truck. A front-sump pan can interfere with a set-forward front ax
• Power Steering Pump – Rotation is engine-specific. A Cummins power steering pump will not work on a CAT engine, and vice versa.

Shop Story: A customer installed a CAT C15 that came out of a Western Star into a Peterbilt 389 and reused the original fan hub. The center height was wrong, so the fan blade sat too high in the shroud.

To compensate, the shop installed a 30" fan blade instead of the recommended 32" blade. Within a few weeks the customer was complaining of high operating temps and the fan running constantly because there was not enough blade capacity to properly cool the engine. Once the correct fan hub was installed that allowed the proper 32" blade, the overheating issues went away immediately.