How do I go about determining the most efficient boost pressure for my IX turbo? I have the compressor map, and I know the sweet spot is the smallest concentric “circle”. I’m just not sure how to read and use the compressor map.

Any guesstimates? I’m not asking what boost will give me the most power. I’m asking what boost will operate the turbo at its peak efficiency.

Thanks,
Jim

 

can you post the compressor map?

 

Edit: Here is the link to the compressor map calculator that I mentioned below: https://www.evolutionm.net/forums/sh...map+calculator


About 10 psi will pass right through the middle of the most efficient island.

Don't worry too much about the efficiency. You're going to be in any one efficiency island for a short period of time anyway.

If you want to know where you will land on the compressor maps of several turbos at varying boost, etc, without doing the math yourself, then search for a thread with an attachment of 'compressor map calculator'. It is a spreadsheet that has a lot of compressor maps in it. I added the VIII compressor map to it, which should be the same as your IX.

If you want to plot the points yourself, here is the math:

The Y axis is pressure ratio. That is (boost level+14.7)/14.7. So, a boost of 22 psi is (22+14.7)/14.7=2.5

The x axis is mass airflow (some are volumetric airflow).

To find mass airflow:

volumetric airflow (CFM):
PR(Cid*VE*RPM/3456)

PR= pressure ratio
Cid - cubic inch displacement - our 2.0L engines = 122 Ci
VE - volumetric efficiency - this changes at different RPMs, depending on hotside of turbo, intake manifold, cams, etc. For a rough estimate, use 1 around 5000-5500 RPM and about .85 at redline.
RPM - self explanatory

Then, you have to convert that volumetric airflow into mass airflow. To get from CFM to lb/min, multiply by .07. This is a big assumption, using standard temperatures. A turbo way out of it's efficieny or a heat soaked intercooler will change the mass flow by a lot.

Anyway, user a few different RPMs and plot your numbers. I will do two quickly for you:

5000RPM, 22psi boost, 100% VE

2.5(122*1*5000)/3456=441 CFM
441*.07=~31 lb/min

So, plot 2.5 from Y axis and 31 lb/min from X axis

7500 RPM, 20 psi boost, .85 VE

2.36(122*.85*7500)/3456=531 CFM
531*.07=~37lb/min

So, plot 2.36 on the y axis and 37 lb/min on the x axis.


Do, the same for a number of different boost, ve, RPM


Eric

 

Boost pressure varies too much with all the determining factors.

 

http://www.turbobygarrett.com/turbob...o_tech103.html