Supercharger belt slip happens when the drive belt cannot transmit enough torque to spin the supercharger at the speed it should, so boost drops or stops climbing at high rpm. Common signs are a squeal under load, boost that falls off near redline, a glazed or shiny belt and black belt dust around the pulleys. Centrifugal superchargers, which spin very fast and make most of their boost at high rpm, are especially sensitive to slip.
Supercharger belt slip symptoms
- Squealing or chirping on hard acceleration or gear changes
- Boost that is lower than expected or drops at high rpm
- Glazed, shiny or cracked belt ribs
- Black dust on pulleys and nearby parts
- Belt jumping a rib or coming off
Common causes
- Not enough tension: a weak tensioner or a belt that has stretched.
- Not enough wrap: the belt contacts too little of the supercharger pulley; idler placement matters.
- Too small a pulley: smaller pulleys for more boost reduce contact area and increase slip.
- Contamination: oil, coolant or belt dressing on the belt.
- Worn or misaligned pulleys.
How tight should a supercharger belt be?
Follow the tension or deflection specification in the supercharger kit’s instructions; correct tension depends on the drive design. Too loose slips and too tight loads the bearings in the supercharger and accessories, so measure rather than guess, and recheck after the first few hundred miles as a new belt settles.
Fixing belt slip
- Clean the pulleys and replace any contaminated or glazed belt.
- Check the tensioner and set tension to specification.
- Confirm pulley alignment.
- Increase wrap with the idler arrangement the kit maker offers, or move to a wider rib count.
- For high boost, consider a cog (toothed) belt drive if your kit offers one.
Is belt grip spray a good idea?
Belt dressings can quiet a squeal briefly, but they attract dirt and can glaze the belt, which makes slip worse over time. Fix the tension, wrap or pulley cause instead.
Belt slip vs other boost problems
Low boost can also come from intake leaks, a bypass valve stuck open or an engine running out of fuel. A boost gauge and a careful inspection separate them; see what does a supercharger do?, centrifugal superchargers and serpentine belt.
ECS Paxton kits
Our East Coast Supercharging Paxton NOVI kits list their belt drives and supporting parts in each listing; browse supercharger kits by platform, including LS3 and C6 Corvette kits.
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