Calculators
7 calculators, and the working behind them
All free, all in the browser, nothing uploaded and no account. Each one sits under a page that writes out the formula it uses, because a calculator you cannot check is a calculator you have to trust — and every one of these is an estimate with assumptions you are entitled to disagree with.
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Compression ratio, and how to work it out
Static and effective compression from bore, stroke, chamber, dish, deck and gasket — with the formulas written out, and a calculator that applies them.
Engine -
Estimating horsepower from airflow
An engine makes power in proportion to the air it can pump. Working from that gives an estimate you can argue with — unlike a multiplier for 'large turbo'.
Engine -
Sizing a turbo from the compressor map
Work out the mass flow and pressure ratio your engine will actually run at — the two axes of every compressor map — then take that point to the maps of the turbos you are choosing between.
Engine -
Sizing fuel injectors
What size injectors a target power needs, what they really flow at your fuel pressure, and why the same set that was fine on petrol is marginal on E85.
Engine -
Lambda, AFR, and what the gauge says
Three ways of writing one mixture, and why a car on E85 at a perfectly good lambda reads 12.1 on a wideband — both numbers correct, only one an air/fuel ratio.
Engine -
Gearing: road speed, rev drop and tyre size
How gear ratios, final drive and tyre diameter set road speed, and how to read the rev drop between gears — the number that decides whether a gearbox suits an engine.
Engine -
Density altitude and dyno correction
How much air there is today, why a hot damp day at sea level is worth thousands of feet of altitude, and what the difference is between an SAE number and a DIN one.
Engine
What they will not do
None of these knows your engine. They take numbers you supply and apply published physics to them, which is worth a great deal when the alternative is a forum post, and worth nothing against a measurement. Where a figure is an assumption rather than a fact — volumetric efficiency, BSFC, compressor efficiency, deck clearance — it is an input you can see and change rather than a constant buried in the arithmetic.
Two of them say so more loudly than the rest. The compression calculator shows what the parts compute to and what Honda quote, because the recovered part data has no deck clearance in it. The turbo one hands you a coordinate and refuses to name a turbocharger, because matching a wheel needs its real compressor map.