What belt lengths are used for the short-belt routings on a Fox-body 5.0?

An 84.5 inch belt bypasses only the smog pump, and a 70.5 inch belt bypasses both the smog pump and the power steering pump. These lengths are for a car with underdrive pulleys; lengths with stock pulleys will vary, though routing stays the same.

What performance gains did the 70.5 inch short belt provide?

On a stock 1990 5.0 Mustang with a 5-speed running slicks at a 1/4 mile drag strip, the 70.5 inch belt gave approximately a 2-tenths decrease in ET and a 1.5 mph increase in trap speed. The 84.5 inch belt showed no measured gain on the same car.

Which direction do the pulleys spin with the stock 5.0 belt routing?

The crank pulley always spins clockwise, the water pump pulley always spins counter-clockwise, and all accessories spin clockwise with the crank pulley.

Is it OK to permanently bypass the smog pump?

Not if you run catalytic converters — the document states permanently bypassing the smog pump will decrease the life of the catalytic converters.

How does the short belt routing differ from the stock routing?

In the short-belt diagrams, the belt routes along the opposite sides of the crank pulley and water pump pulley compared to the factory belt.

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Ford 5.0 Fox Mustang Short Belt Routing Diagram - 84.5" & 70.5" vs Stock

Serpentine belt routing diagrams for short and stock 5.0 belts with explanatory text

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Belt routing schematic comparing 84.5, 70.5 short and stock 5.0 serpentine belt paths around accessory pulleys.

AI caption July 2017 · Photo 428 of 911

This document is a screenshot of a forum post showing a serpentine belt routing reference diagram for the Ford 5.0L (302) V8 engine as used in Fox-body Mustangs. Three routing diagrams are shown: an 84.5-inch short belt (bypassing only the smog pump), a 70.5-inch short belt (bypassing both the smog pump and power steering pump), and the stock factory-length 5.0 belt routing with all accessories labeled (tensioner, A/C compressor, alternator, water pump, smog pump, crankshaft pulley, and P/S pump). The captions explain that in the short-belt routings the belt wraps the opposite sides of the crank and water pump pulleys compared to stock, that the crank pulley always spins clockwise and the water pump counter-clockwise, and that all accessories spin clockwise with the crank. Belt lengths cited are for a car with underdrive pulleys; stock-pulley lengths will vary but routing is the same. Quarter-mile testing on a stock 1990 5.0 Mustang with a 5-speed showed roughly a 2-tenths ET reduction and 1.5 mph trap speed gain with the 70.5-inch belt, and no measurable gain with the 84.5-inch belt. It also warns that permanently bypassing the smog pump will shorten catalytic converter life. The forum poster asks whether the reroute improves water pump pulley belt traction.

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Frequently asked questions

What belt lengths are used for the short-belt routings on a Fox-body 5.0?: An 84.5 inch belt bypasses only the smog pump, and a 70.5 inch belt bypasses both the smog pump and the power steering pump. These lengths are for a car with underdrive pulleys; lengths with stock pulleys will vary, though routing stays the same.
What performance gains did the 70.5 inch short belt provide?: On a stock 1990 5.0 Mustang with a 5-speed running slicks at a 1/4 mile drag strip, the 70.5 inch belt gave approximately a 2-tenths decrease in ET and a 1.5 mph increase in trap speed. The 84.5 inch belt showed no measured gain on the same car.
Which direction do the pulleys spin with the stock 5.0 belt routing?: The crank pulley always spins clockwise, the water pump pulley always spins counter-clockwise, and all accessories spin clockwise with the crank pulley.
Is it OK to permanently bypass the smog pump?: Not if you run catalytic converters — the document states permanently bypassing the smog pump will decrease the life of the catalytic converters.
How does the short belt routing differ from the stock routing?: In the short-belt diagrams, the belt routes along the opposite sides of the crank pulley and water pump pulley compared to the factory belt.