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My CFM calculator

Enter the peak boost you plan to run and the rpm in which you plan to reach it (or leave blank for simplification) and the displacement in CU (there is a check box to change it to CC units).

This will give you two numbers for each rpm point: Pressure ratio (PR) and air flow (in cfm) for your motor.

All you have to do is look at any compressor map and plot PR vs air flow (in cfm or lb/hr). You want your plot to stay withing the most ideal part of that compressor map.

The map has rings. The rings represent the compressor effeciency at a given point. There is also a line show compressor rpm. The higher the compressor rpm, the hotter the air will be and the harder the turbo will be working (read: longivity). If your plot gets to the left of the chart (off of the chart) the compressor will surge. This usually happens when you try to put a turbo that is too big for a car.

Now the links!

This is what you should read first. It pretty much teaches you everthing you need to know about turbos and maps:
http://www.badbricks.com/main_files/faqs/turbo_size.htm (link not currently working)

here is a site that plots it for you on top of various charts:
http://www.bsmotor.com/turbo/kalkuler.html

on the sites that don't plot it for you, or if you find a chart elsewhere, you just print out the compressor map and draw it in with ink.

turbonetics compressor maps:
http://www.turboneticsinc.com/comp_maps/fig1.html

garret compressor maps:
http://www.bsmotor.com/turbo/tabell.html

Mitsubishi turbos upgrade guide and well as some GOOD tech info http://www.3si.org/member-home/jlucius2/j2-2-turboguide.htm (link not currently working)


After reading all of this and understanding it, you'll pretty much know all you need to about turbos (beside actually getting hands-on experience).

-C

This almost seems like a FAQ.

[EDIT] I forgot I added the cfm to lb/hr conversion checkbox on my calcuation page.
 
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