READING TURBO COMPRESSOR MAPS, PART I

By 460-BBF-Turbo-In-CC (adapted from the legendary Car Craft turbo blog)

"Somewhere there is a map of how it can be done."

-- Ben Stein

Turbo manufacturers create compressor and turbine maps to summarize the air flow and density characteristics of turbochargers. Sadly, these maps are often withheld from grassroots Car Crafters (especially turbine maps).

But when you can find them, these maps are invaluable guides in turbo selection . . . if you know how to read them.

The next few [articles]are going to be about reading turbo maps.

To make these tips more relevant to our discussion of turbocharging a big-cube V8, here's a turbo compressor map for an old Garrett T66 (a pair of these would support well over 1,000 h.p.).

The first thing to notice is the left vertical axis of the map. Pressure ratio is simply the relationship between compressor discharge pressure to atmospheric pressure.

However, it is NOT a direct measure of how dense the compressed charge is because of charge heating during compression and atmospheric conditions outside of the turbo. (If it were, we wouldn't need the map!)

1.00 is basically no compression (compressor discharge pressure = ambient (outside) pressure)

2.00 means the discharge pressure is twice as much as ambient pressure.

3.00 means the discharge pressure is three times as much as ambient pressure.