Turbo's
complexx:
Although your question is posed to djres4, I'll take a whack at it.
correct me if I'm wrong, but you can't be at more than one place on those maps at the same time right?
Well the answer to that is sorta yes and no
.
Your correct at any given moment you can only be at one point on the map,
but at any given boost (pressure ratio) you can be at many different points on the map.
Look at the 13G compressor map for example at the 2.0 pressure ratio line. You see that if you draw a horizontal line across the map at the 2.0 pressure ratio it can flow anywhere from about 100 cfm at the surge line on the far left side to about 360 cfm on the far right side. This is an example of the fact that a turbocharger is a fixed pressure, variable volume compressor.
You use the waste gate system to define a pressure ratio for the turbo to run at but it can flow a wide range of air flows at that pressure ratio.
The obvious question is how do you determine the point on that line that corresponds to the turbo's true point of operation?
That left right postion, is defined by the air flow demand of the engine the turbo is attached to, and the turbos inlet air temperature and pressure (which we will ignore for now).
If you turn a 2.0L engine at 4000 rpm and it has a .85 VE it will try to ingest about 240 CFM or in this example, right about where the right side of the 75% effeciency island intersects the 2.0 PR line.
Push the engine rpm up to 6000 rpm and now the engine wants to flow 360 cfm which is the maximum rated flow of the turbocharger. (at least at reasonable effeciencies).
As you can see at the midrange rpms around 3000 - 4000 rpm the 13G is a highly effecient turbo that will easily support boost pressures over 14 psi. It hits a maximum practical flow of about 300 CFM about 25 psi with acceptable effeciency, when the engine hits about 5000 rpm. ----- Hmmm that sounds a lot like the rpm range the WRX hits maximum torque doesn't it
If you have a boost controller that allows you to map boost pressure to engine rpm, or if you fiddle with a more basic boost controller so it hits peak boost at around the peak torque rpm of 4500 - 5500 the 13G will make you a very happy driver.
I think the thing you need to keep in mind is
the turbo is not an independent unit, it is part of a co-dependent system.
You can't define the turbo's performance until you know something about the engine it will be used on and its breathing ability, tune and rpm range.
Larry
