Boost calculator

What the blower will actually make

Put your engine size, rev limit and pulley sizes in and this works the boost out the same way our own tables do. It is arithmetic, not a promise — but it will tell you straight away whether a pulley choice is sensible.

Engine size cc · 1300–2100 is the AMR 500’s range Max engine speed rpm · where you expect to be pulling Crank pulley mm · 170 is the stock aircooled pulley Supercharger pulley mm · 60 is what we supply as standard

Realistic boost 8.5psi

Static compression to aim for: 7.5:1 – 8.5:1

Their recommended range for 8–10 psi. Lower compression buys detonation margin.

Drive ratio: 2.83 : 1
Blower speed: 14,167 rpm
Blower flow: 7,083 L/min
Engine flow: 4,103 L/min
Pressure ratio: 1.73
Ideal boost: 10.7 psi

Blower at 14,167 rpm, inside the 16,000 rpm limit.

60 mm

8.5 psi

What we supply as standard.

70 mm

5.6 psi

Not an off-the-shelf part for the AMR 500 — special order, so ask first.

80 mm

3.5 psi

The mildest of the three. Least stress on a standard engine.

The working

Nothing up our sleeve

Every figure above comes out of these seven lines. The AMR 500 is a 500cc-per-revolution Roots blower, and a four-stroke engine swallows half its capacity per revolution — the rest is division.

drive ratio = crank pulley ÷ supercharger pulley

blower rpm = engine rpm × drive ratio (16,000 rpm ceiling)

blower flow = 0.5 L/rev × blower rpm

engine flow = litres × engine rpm ÷ 2

pressure ratio = blower flow ÷ engine flow

ideal boost = (pressure ratio − 1) × 14.7 psi

realistic boost = ideal × 0.8 (efficiency and leakage)

The 20% comes off for what the arithmetic can’t see: volumetric efficiency below 100%, supercharger leakage, intake restriction and charge heating.

Find which kit fits Ask us about your build

Read this too

These are estimates, not a warranty

What moves the number

Engine condition and age
Installation quality
Ambient temperature and altitude
Fuel system, exhaust and ignition
Tuning method and calibration accuracy
Variation between individual engines and components

Where we stand

Any boost chart, performance graph, airflow calculation or projection on this site is a theoretical estimate based on mathematical modelling, idealised conditions and controlled assumptions. It is general guidance.

We don’t guarantee that any customer will reach the boost or power shown here, and none of it should be relied on as a promise or a warranty. Making sure your engine and supporting systems suit the intended performance level is down to you.