What belt length bypasses the smog pump on a Fox body 5.0 Mustang?

An 84.5 inch belt bypasses only the smog pump (with underdrive pulleys installed; stock pulleys require a different length).

What belt length bypasses both the smog pump and power steering pump?

A 70.5 inch belt bypasses both the smog pump and the power steering pump on a Fox 5.0 with underdrive pulleys.

Does a short belt improve performance on a 5.0 Mustang?

Per the document, the 70.5 inch belt gave about a 2-tenths decrease in ET and 1.5 mph gain in trap speed on a stock 1990 5.0 Mustang 5-speed; the 84.5 inch belt showed no measured gain.

Which direction do the pulleys spin with the stock 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 safe to bypass the smog pump permanently?

The document says if you run catalytic converters, permanently bypassing the smog pump is not recommended because it will decrease catalytic converter life.

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Fox Body Mustang 5.0 Serpentine Belt Routing Diagram - Stock & Short Belts

Serpentine belt routing diagrams for a Fox-body 5.0 Mustang with explanatory text

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Belt routing diagrams comparing 84.5-inch and 70.5-inch short belts to the stock 5.0 serpentine belt path with explanatory notes.

AI caption February 2011 · Photo 737 of 956

This document is a computer-drawn schematic showing three serpentine belt routing options for the 5.0L engine in Fox-body Ford Mustangs. The bottom diagram (green) shows the stock 5.0 belt routing with all accessories labeled: tensioner, A/C compressor, alternator, water pump, smog pump, crankshaft pulley, and power steering (P/S) pump. The upper-left diagram (blue) shows an 84.5-inch short belt routing that bypasses only the smog pump, while the upper-right diagram (red) shows a 70.5-inch short belt that bypasses both the smog pump and the power steering pump. The text explains that in the short-belt routings, the belt wraps opposite sides of the crank and water pump pulleys compared to stock; the crank pulley always spins clockwise, the water pump pulley counter-clockwise, and all accessories spin clockwise. Belt lengths given are for a car with underdrive pulleys; stock-pulley cars require different lengths but identical routing. Drag strip testing on a stock 1990 5.0 Mustang 5-speed showed the 70.5-inch belt improved ET by about 2 tenths and trap speed by 1.5 mph, while the 84.5-inch belt showed no measurable gain. It also warns that permanently bypassing the smog pump will shorten catalytic converter life.

This document covers 1990 (test vehicle; applies to Fox body, which may differ from this 1986 Ford Bronco.

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Frequently asked questions

What belt length bypasses the smog pump on a Fox body 5.0 Mustang?: An 84.5 inch belt bypasses only the smog pump (with underdrive pulleys installed; stock pulleys require a different length).
What belt length bypasses both the smog pump and power steering pump?: A 70.5 inch belt bypasses both the smog pump and the power steering pump on a Fox 5.0 with underdrive pulleys.
Does a short belt improve performance on a 5.0 Mustang?: Per the document, the 70.5 inch belt gave about a 2-tenths decrease in ET and 1.5 mph gain in trap speed on a stock 1990 5.0 Mustang 5-speed; the 84.5 inch belt showed no measured gain.
Which direction do the pulleys spin with the stock 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 safe to bypass the smog pump permanently?: The document says if you run catalytic converters, permanently bypassing the smog pump is not recommended because it will decrease catalytic converter life.