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Supercharger Pulley Calculator

2026-09-27 6 min

Required blower pulley diameter for a target boost — solve the belt-drive equation backwards.

Blower Pulley
3.92 in
Blower Speed
10714 RPM

Calculator

Target Boost(psi)
psi
Blower Rated Boost(psi)
psi
Engine RPM(RPM) Help
RPM

RPM where target is wanted

Crank Pulley(in)
in
Results update live as you type

Live statistics

Blower Pulley

3.92 in

Blower Speed

10714 RPM

Results

Optimal

Blower Pulley

3.92in

Blower Speed

10714RPM

Planning estimate from standard automotive formulas. Validate with dyno, timeslip or datalog data when precision matters.

Visualizations

Results overview

3.9Blower Pulley
10,714Blower Speed

Blower Pulley vs. Target Boost

Blower Pulley

3.9in
26

Formula

Inverted pulley math: from desired boost to required blower speed to the pulley diameter that produces it.

Needed blower RPM = target ÷ rated × 15,000; pulley = crank × engine ÷ blower RPM

Variables

SymbolNameUnitDescription
targetDesired boostpsiAt the RPM below
ratedBlower ratingpsiAt 15,000 blower RPM
crankCrank pulleyinFixed drive side

Explanation

Round to the nearest available pulley (usually 1/8 in steps) and verify belt length changes.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Record the inputs.

Target Boost:10 psi
Blower Rated Boost:14 psi
Engine RPM:6000 RPM
Crank Pulley:7 in
Result: 4 inputs ready
Step 2

Apply the formula.

Needed blower RPM = target ÷ rated × 15,000; pulley = crank × engine ÷ blower RPM
Result: Primary result = 3.92 in
Step 3

Read every derived output.

Blower Pulley:3.92 in
Blower Speed:10714 RPM
Result: Blower Pulley = 3.92 in
Final Answer
3.92

Worked Examples

See how the calculator works with different scenarios.

Scenario

10 psi wanted, 14 rated, 6,000 engine, 7 in crank.

Inputs

Target:10 psi
Rated:14 psi
Eng:6,000
Crank:7 in

Calculation

blower = 10,714 RPM; pulley = 42,000 ÷ 10,714 = 3.92

Result

3.92 in — buy the 4.00 in pulley.

Interpretation

Nearest shelf size lands ~9.8 psi — close enough to tune around.

Understanding Your Result

Your Result: Blower Pulley: 3.92 in

What This Means

Blower pulley diameter that delivers your boost goal.

Why It Matters

Turns pulley shopping from folklore into one calculation.

Professional Interpretation

Treat the primary result as a planning estimate, then validate on a dyno, at the track, or with logged sensor data. If measured numbers disagree by more than ~10%, re-check inputs (units are the usual culprit) before changing parts.

Recommendations

  • •Double-check units on every input before trusting the result
  • •Compare against the worked example below to sanity-check magnitude
  • •Validate with measured data (dyno, timeslip, datalog) when it matters

Learn — fuel economy, deeply

Target boost in, pulley size out — the blower shopping equation solved backwards.

1 · Where the gallon goes (energy path)

Engine heat

60–70% lost

Coolant + exhaust carry most energy away. Hybrids recover some via Atkinson cycle + regen.

Driveline

5–15% lost

Transmission, differential, accessories. CVTs and 8–10 speed autos lose less.

Aero drag

∝ v²

Doubles from 55→78 mph. Roof boxes hurt more than trunks.

Rolling + brakes

10–20%

Tires, weight, stops. Regen braking (hybrid/EV) reclaims city braking energy.

4 · Measure like a pro (the 3-tank protocol)

  1. Fill to first click at the same pump, record the odometer (Tank 0).
  2. Drive normally for 2–3 tanks; always refill to first click at the same pump.
  3. MPG = total miles ÷ total gallons across all tanks — averaging kills pump-click noise.
  4. Cross-check with the trip computer; a persistent >10% gap means the computer needs calibration — or the car needs service.
  5. Log with an OBD-II dongle for per-trip MPG if you want to isolate commute vs. highway behavior.

Practical Tips

  • •Start from the default values — they describe a typical combination
  • •Use the sensitivity chart to see which input moves the result most
  • •Keep units consistent (all inches or all mm, never mixed)

Common Mistakes

Mixing units (inches with mm, psi with kPa)
Convert every input to the unit shown on its field before calculating.
Trusting a single output blindly
Cross-check with the worked example and, when it matters, a dyno or datalog.

Assumptions

This calculator makes the following assumptions to provide estimates:

Steady-state model: Formulas assume stabilized conditions; transients, heat soak and traction limits are excluded.
Standard factors: Empirical constants (BSFC, VE, drivetrain loss) use typical values — your combination may differ.

Limitations

Be aware of these limitations when using this calculator:

Estimate, not measurement: Predictions carry real-world scatter of roughly ±5–15% depending on the model.
No transient effects: Shift time, wheelspin, spool lag and heat soak are not modeled here.

Frequently Asked Questions

Answers to common questions about this calculator.

Belt length changes?
Yes — smaller pulleys need shorter belts; check tensioner travel and wrap.
Overspin risk?
Never exceed the blower’s max RPM — bearings and rotor coatings fail fast beyond it.

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Related Guides

Deepen your understanding with these educational resources.

Glossary

Technical terms used in mortgage calculations explained in plain language.

MPG
Miles per gallon. Distance travelled per gallon of fuel; higher is better. US gallon = 3.785 L.
L/100 km
Litres consumed per 100 kilometres; lower is better. Standard metric efficiency unit.
MPGe
Miles per gallon-equivalent. EV metric: miles travelled on 33.7 kWh (energy of 1 gal of gasoline).
CAFE
Corporate Average Fuel Economy — US fleet-average efficiency standard enforced by NHTSA.
Rolling resistance
Energy lost deforming tires as they roll. Low-pressure or wide tires raise it.
Aerodynamic drag
Air resistance growing with the square of speed — why highway MPG falls fast above 60 mph.
Hypermiling
Driving techniques (coasting, steady speed, anticipation) that maximise real-world MPG.
OBD-II
On-board diagnostics port. Scanners and dongles read live MPG, fuel trim and fault codes.

Authoritative References

Trusted sources and standards referenced by this calculator.

Applicable Standards

EPA Fuel Economy Testing (40 CFR Part 600)CAFE — Corporate Average Fuel Economy Standards (NHTSA)WLTP — Worldwide Harmonised Light Vehicle Test ProcedureSAE J1321 / J1711 — Fuel consumption test proceduresISO 2575 — Road vehicles symbols & efficiency markings

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