Basically this is how to size up a turbo to your motor....all examples will be on an assumed base of a 1.6L 4valve @ 8psi on a T3-Super60... feel free to use your own numbers. NOTE: This guide is only for maps that are in US Customary units (inch, pound, second). You would have to do the conversions for SI units

This is a compressor map for the T3-Super60 turbo. The first thing you notice is the left hand colum. The left hand column is the PRESSURE RATIO. What does that mean?? Simple... here's a forumla for ya.

Pr = (Bp + Ap) / Ap

Pr = pressure ratio

Bp = boost pressure

Ap = atmospheric pressure which will always be 14.7 (this is the static barometric pressure at sea level, you can tune for specific elevations and atmospheric conditions if you want... but no need)

Okay here we go, it's just plug and chug to find Pr

Pr = (8+14.7) / 14.7

Pr = 1.54

Now pull out your map and go up the left side of the graph and find 1.54 and draw a line @ 1.54 parrell to the x axis

Next comes the bottom of the graph (aka the x-axis) it should read CFM or AirFlow lb/min ....since there is no formula for lb/min we find cfm first and convert. New formula alert

Cfm = (L * Rpm * VE * Pr) / 5660

L = liters of the motor

Rpm = the revs you are searching for....ususally redline

Ve = Volumetric efficiency

basic numbers...not exact: 2valve = 85 4 valve = 90 ported = 95

okay so we got to plug and chug again..

Cfm = (1.6 * 7000 * 90 * 1.54)/5660

Cfm = 274.3

Note: This is a simplified formula. There is a more explicit way to make this conversion, found here... http://xs210.xs.to/xs210/06516/computation.JPG )

Now to convert that to lbs/min: Lb/min = (cfm).07

Lb/min = 19.2

[i]note: this assumes a standard density for air, again this changes due to temp and elevation much like pressure, but for initial tuning choose this number as a constant)

Okay now you got one more number to plot...find 19.2 on the x axis and plot a line parrell to the y axis....this should cross the line you made for 1.54

This line will tell you if you're gonna run out of breath at redline...

Next you need to plot a line at 50% rpm...that's simple to do as well....take your Lbs/min and multiply by .5 ie: (Lbs/min).5 = 50% Rpm (assumingly but works good enough)

so (19.2)(.5) = 9.6

Plot 9.6 on your x axis...then of course...draw a line parrell to the y axis

You need to make sure that you are on the right side of that surge limit line

note: the surge limit is the physical limit as to the airflow of the turbo. crossing this line will result in backspin... damaging your turbo and possibly engine

Now to the last point. and this is kinda tricky... but I'll try and explain easily....

We need to make sure that from 20% to your already Okay'd 50% that no where on that line will it cross the surge limit.

We need to set this at Pr=0 (NO BOOST... this assumes no launch control and that you will only start to spool at 20% of your RPM band, 1400rpm in this case)

so we take our lb/min and multiply that by 20%

(19.2)(.20) = 3.84 (about 4)

Now go to the x axis again...and plot your point at your 20% rate...which is 4 in my case....now instead of drawing a line parrell to the y axis...draw a line from your 20% to your 50%.....should be an angled line...

as long as that line stays to the right of the surge limit ....you're in the clear!

That my friends is basic reading of compressor maps for turbos. Keep in mind, this is not exactly perfect, but it gives you an idea of how the turbo is going to react. Always allow yourself some error room on the map... DO NOT GET TOO CLOSE TO THE SURGE LIMIT.

This way of mapping assumes a single boost pressure. If you have staged boost controllers, there is a different proceedure. There is also a different proceedure for anti-lag and launch control. Anyone interested in the advanced mappings, PM me and I'll try to elaborate.

Quick Tips For Turbo Selection

- The "rings" on a turbo map show the different areas of efficiency. Each line is marked with the efficiency level that the area it contains is. The more efficient the turbo, the less heat and less turbulence is created, which means more power, more reliability, and better engine health during boost. Try to stay inside the "sweet spot" or inner most part of the map where efficiency is highest

- The surge limit of the turbo is the max pressure the turbo can deliver for a particular flow rate. Pushing a turbo further than the surge limit can cause the turbo to spin backwards, thus sucking air from the engine, or even starve the engine for air because it cannot meet the demands of the breathing cycle. Stay AWAY from the surge limit.

- As the map dissappears to the right, the turbo reaches high speeds and high temperatures. While the turbo can function far to the right, it isn't not a good place to be and can cause damage to the turbo due to heat or over-spinning. Again, try to stay near the sweet spot.

Shortcuts

ONLY DO THESE AFTER YOU UNDERSTAND THE MATH AND REASONING!!!

Excel sheet to convert everything for you: http://www.northtexasneons.org/shawn/mi ... fmCalc.xls

ONLY CHANGE THE BLUE CELLS

Java Program: http://www.turbofast.com.au/turbomap.html

There are a number of maps there and it also accounts for intercooler pressure drop, water injection, etc

Another source of info: http://www.turbosaturns.net/articles/co ... 20maps.htm

Post any questions in here and I'll try to clear it up.