This is a collection of turbo maps with curves mapped for whiteblock engines. Engine size is assumed to be 2.3L, although there won’t be much of a difference for 2.4L and 2.5L engines.
The lines drawn in the maps below indicate the efficiency area in which the turbo would operate at a given boost pressure on a Volvo whiteblock engine. The data for these compressor maps is taken from actual datalogs.
For a full description of how to read compressor maps, please see Garret’s collection of Compressor Map Terms
By comparing the two maps above you can see that although the 16t is an upgrade over the 15g, it is only marginally so. Anything above 17psi on either of these turbos and the efficiency quickly drops off. Even at 17psi the efficiency is less then 60%. When pushing a 15g/16t to 17psi a high quality intercooler is a extremely worthy investment.
As you can see, the efficiency drops off greatly at anything above 20psi on a 19t. The line drawn for 30psi was an extrapolation, since a 19t can’t actually spin fast enough to supply 30psi on a whiteblock engine.
A whiteblock with a GT28 will stay out of the turbo’s inner most effciency islands, but this turbo can still supply 23psi at above 70% efficiency quite comfortably.
A bit of a step up from the Garrett 71 compressor wheel, the 20G can supply up to 25psi at an efficiency of 70-73%. This is for a standard, cast wheel 20G.