Turbo Analyzer

The Turbo Analyzer is the moving-picture version of the Turbo Calculator. Where the calculator gives a single operating point, the analyzer sweeps the whole rev range and plots the engine’s operating line — the path the compressor walks from spool to redline — so you can lay it over a manufacturer’s compressor map and see whether the engine stays inside the efficient envelope all the way. Open it from Analysis › Turbo Analyzer.

Figure 1

The inputs

• Engine + RPM sweep — displacement and the RPM start, end and step: the range the line covers and how finely it is drawn.
• Volumetric efficiency ramp — VE at the start RPM, at a peak (an RPM and a value) and at the end RPM: a three-point VE curve so the engine breathes realistically across the range instead of at one fixed figure.
• Boost profile — boost at the start, at spool/peak (an RPM and a psi) and at the end: models boost building as the turbo spools and tapering near redline.
• Ambient + intercooler + compressor — atmospheric pressure, ambient temperature, intercooler ΔP, intercooler effectiveness (default 70 %), compressor efficiency η (default 70 %) and a target AFR.
• Surge & choke lines — two points each, so you can draw your compressor’s surge (left) and choke (right) limits straight from its map and judge the operating line against them.

Reading the plot

Click Plot and each RPM in the sweep becomes a point at its mass flow (horizontal) and pressure ratio (vertical); joined up they form the operating line. Overlay it on the real compressor map, or read it against the surge/choke lines you entered: a healthy match keeps the line clear of the surge limit at low RPM, out of choke at the top, and through the map’s efficient islands in between. A line that pushes into surge when the turbo is spooling, or runs off into choke near redline, is the sign of a mismatched compressor.

Tip — set one operating point in the Turbo Calculator first to learn the numbers, then come here and let the VE and boost ramps turn that single point into the whole curve. Tweak the ramps to match how your setup really spools.

See also

• Analyzers
• Turbo Calculator
• Air Flow Estimation