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Compressor Flow Maps and Calculations

Time:2012-04-05 12:51Turbochargers information Click:

Tu horsepower Lovehorsepower

At 7200 RPM we have 35.6lb/min.

Some Comments/Opinions

Check out the new CFM calculator. It will generate a table with varying RPM given boost, volumetric efficicency, max engine RPM, and engine size.


The above two diagrams were pulled from 'Forced Induction Performance Tuning'.

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Plotting 25psi:
Here is an interesting one, this compressor, despite being larger, cannot make the 29psi that the 50 trim can.  The graph doesn't even extend to a pressure ratio of 3.0.  At boost levels of around 18-25psi, however, it is extremely efficient and hence will make more power at those boost levels.

For 7200RPM:

How about that 60 trim Garrett compressor.
RPM = maximum engine speed (we'll adjust this later)

Plotting our points results in:


Great resource for compressor maps.

400HP - exducer bore between 61mm and 70mm

There is yet another item we can determine from the compressor map.  We want to make sure that the turbocharger selected will not operate to the left of the 'surge line'.  The above graph does not specify a surge line, but it is to the left of any point within the largest island on the graph.  Check out the T04E-46 and 50 trim maps below, they include a surge line on the graph.  A good approximate method for checking to be sure we are away from the surge line, is to plot one more point on the compressor map.  This is 20% airflow at a pressure ratio of 1.0.  Then connect that point with the 3600RPM point.

Whoops! - Off the graph.  So we know that this compressor and the MR2's 2.0 liter engine cannot run 25psi at 7200RPM.  Doing the same for the TD06-20g compressor:

Just makes it!  Again, keep in mind that more boost can be made at lower RPMs, but it will just start to drop off to about 29psi as the RPMs rise.

200HP - exducer bore between 41mm and 51mm

Great!  The line plotted from 20% max airflow to our 3600RPM point falls to the right of the surge line.  If this line fell to the left at any point, this compressor would not be a good choice.  If the turbocharger operates to the left of the surge line, the compressor will be unstable, and will eventually damage the compressor.  From this, the TD06-20G compressor is a wonderful fit for the MR2 turbo.  Now that we have these numbers, we can plot them on other compressor maps.

20% airflow, in our example is 101.6CFM or 7.12lb/min.  Plotting this point and connecting the dots:

The Compressor

From these two points (where the above red lines intersect), this compressor looks like a great fit.  According to the compressor map it can make 18psi by 3600RPM, and at 7200RPM it is in the 76% efficiency 'island'.  The higher the efficiency island the lower the outlet temperature of the compressed air, and hence the more power you can make.  This map also includes compressor RPM as denoted by the numbers on the graph 55000rpm, 75000rpm and so on.  At 7200 engine RPM, and making 18psi of boost, the compressor RPM is between 105,000 and 120,000RPM.  This means that the compressor is capable of supplying this type of spool up, but only when matched with a correct sized turbine for your application.  See '' below.


We need to plot our two points on this map:

Since this is the internet and I can write whatever I want....
Stock 4-valve = 90%

The turbocharger compressors that I will be comparing are the TD06 20G compressor from Mitsubishi that comes with a couple of the Greddy kits, the T04E-46, T04E-50, and the T04E-60 trim compressor wheels from Garrett.  This method and formulas was taken from A. Graham Bell's excellent book, 'Forced Induction Performance Tuning'.
Pr = (14.7 + 29) / 14.7 = 2.97
Now lets calculate airflow.  I think it's best to calculate airflow at at least two different RPM points.  For our example, let's say we want to have full boost by half of max RPM.  Redline on the MR2 is 7200RPM.  So we'll calculate airflow for 3600RPM and 7200RPM, and then see which map works out best for these values.  We'll choose 90% for volumetric efficiency (VE).

Looks like we cannot make 18psi by 3600RPM with this compressor, so it is going to have slightly more lag than the above two compressors.  At 7200RPM, we are just out of the 78% efficiency island, and with room to spare for more boost.  So how do we make sure that we are not to the left of the surge line?  If you draw a line from 20% airflow (7.12lb/min) to the 3600RPM point (17.8lb/min), the line is to the right of the surge line right up until the intersection.  The method for determining if you are to the right of the surge line is an approximate one, and suffice it to say, will not work if the compressor doesn't make full boost by half of redline as the method prescribes.  That said, given this compressors record, it does not operate in surge with the 2.0 liter MR2 engine.  An explanation of this is beyond the scope here.  Surge usually can be noticed by a pop or backfire out of the compressor inlet.

A/R is the real important dimension for judging a turbines potential.  It is determined by dividing the area of the turbine nozzle A by the radius R from the center of the turbine axle to the center of the housing throat.

500HP - exducer bore between 67mm and 78mm

Last Updated on Saturday, 01 January 2011 21:01  

CFM at 7200RPM = (2.0 x 7200 x 90 x 3.08) / 5600 = 680.6CFM or 47.6lb/min

By Joseph Obernberger

There seems to be a lot of confusion about which turbocharger to choose for which application.  These are some notes and calculations for the MR2 Turbo and which maps I think are best for this 2.0 liter engine.  If anything is wrong here, please , and I will make the corrections.


The Turbine Side

Click here for a CFM Table of the 2.0 liter MR2 engine.

Clearly there is more lag with this compressor, but it is over 78% efficient at 7200RPM and 18psi of boost!  Again, surge is a consideration, and from word of mouth from those using this compressor, it doesn't seem to exhibit surge problems.  That said, I have not tried it myself.

Valid intersections are denoted by arrows.  Plotting this point for the T04E-46
Pr = (14.7 + 25) / 14.7 = 2.70

First we need to calculate the engine air flow rate (CFM).  The formula for this is:

Now we can look at some compressor maps and see where these points fall.  Let's take a look at the TD06 - 20g compressor map first.

Compressor Flow Maps and Calculations

Thursday, 30 December 2010 17:26 Joe


Pr = 14.7 + Boost
CFM = (2.0 x 3600 x 90 x 2.22) / 5660 = 254.1 or 17.8 lb/min.  As a side note, since half the RPM will result in half the airflow, 254.1 is indeed half of 508.32

Here at 18psi of boost and 7200RPM we are at about 73% efficiency.  This turbo will also make 18psi by 3600RPM, and we are very safe from surge.  Looking at this map, it is clear that this compressor is smaller than the TD06-20G and will spool faster.  Just for fun, we can see where on this plot we will be at 25psi of boost.
VE = engine volumetric efficiency.  From A. Graham Bell's book Forced Induction Performance Tuning some good values for VE are:

To calculate the pressure ratio you need to know what boost pressure you want to run and then plug that into the following formula:

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