How to read and formulate a compressor map.

[Töuge-MR]

By: Chris schnell, Brad ligget.

Here are the variables you must determine. Some of them include temp, others include your motor.


(How much PSI you plan to run)PSI= 18
(How much PSI loss your IC will generate)IC loss 1.2lbs
(atmospheric pressure for your state)atmosphere 14.7
PCO (pressure out of compressor) 34.2
PR (pressure ratio) 2.3265
IC air temp 150 degrees
DI = 0000838
5,000 RPM
MF (mass airflow rate) 29.0443
Outside Temp 75F
CMf = 25.45lbs per min


**The perfect turbo will be 100% efficient, which means the car will have to work 0% to spool it, which doesnt exist. The Mines' Skyline GT-R's HKS turbos are 81% efficent on that car. Anywhere from 70%+ is good.

1)ok..we have 18lbs of boost, we will assume 1.5 psi of pressure drop across the intercooler.
1) 18lbs boost
2)1.5 psi drop across intercooler
3) 14.7 psi atmoshperic pressure for sea level

This is where you calculate the PCO, or the pressure out of the compressor.
(Pco= boost+ atmo. pressure+ intercooler drop)
18+ 14.7 + 1.5
-------------------
PCO=34.2

*Now we need to find the Pressure Ratio (PR), which is PCO / atmospheric pressure
34.2/14.7
----------------
PR=2.3265

Now we have to find the Density of the air (DI) after the intercooler. A good aftermarket intercooler will rate the air comming out at about 130 degrees F, so for a stocker put 150F.

Di= boost pressure+ atmospheric presssure/ R x 12 x (460+ post intercooler temp)
or
18 + 14.7 divided by 53.3 x 12 x (460 + 150)
---------------------
DI=0000838


*Now we need mass airflow rate (MF), but first you have to find the RPM range that you want to measure it at. You can redo this equasion once for every RPM you want it for. I measured at 5,000RPM because thats about where any turbo on my car would be at its peak.

MF=Di x displacement in cubic inches x RPM / 2 x volumetric eff.
i would say my engine is at 88% volumetric efficy.
MF= 29.04

*Find the displacement of your motor in cubic inches. Mines a 2.OL, so 2000 cc (2.0l) x 16.387.


*Okay, now we have to correct it. The computer uses numbers for standard test conditions.
CMf= Mf x the square root of 545 degrees rankin/ ambiant temp in degrees rankin / atmo pressure/ comp inlet pressure.

So find the temperature outside it is durring this "test". I chose 75 degrees F.
(F deg. + 460 = deg R[rankin] )
so 75 + 460= 465
----------
CMf= 29.04x square root of 465 R

29.04 x .9236942 / 1.0537634 = 25.4555

CMF = 25.45
--------------------------------------------------------------------
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Now print the map out.
"Trace your pressure ratio over until it intersects with the air flow required to achieve your flywheel hp.At this point you are looking at the efficiency percentage at which your turbo is currently working
It should be above 60% minimum...........the higher the better"



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[4g63ownedu]

 

[Töuge-MR]

lol.

[Töuge-MR]

Heres an example of what it should look like when youre all done. Here is the 46 trim T04E on my MR2.



As you can see, this turbo will meet my spool demands almost to a tee.

[4g63ownedu]

I'm still undecide on exactly what turbo to get. I'm probably going to get something in the 20g range. Anything smaller will spool too quickly if I do the 2.3 stroker. But this is a couple years off yet, so only time will tell.

[rotarded]

How's this?

[rotarded]

Touge,

To the left of the surge limit line on the flow map is the surge area where compressor operation can be unstable. Typically, surge occurs after the throttle plate is closed while the turbocharger is spinning rapidly and the by-pass valve does not release the sudden increase in pressure due to the backed-up air. During surge, the back-pressure build-up at the discharge opening of the compressor reduces the air flow. If the air flow falls below a certain point, the compressor wheel (the impeller) will loose its "grip" on the air. Consequently, the air in the compressor stops being propelled forward by the impeller and is simply spinning around with the wheel, which is still being rotated by the exhaust gas passing through the turbine section. When this happens, the pressure build-up at the discharge opening forces air back through the impeller causing a reversal of air flow through the compressor. As the back pressure eventually decreases, the impeller again begins to function properly and air flows out of the compressor in the correct direction. This sudden air-flow reversal in the compressor can occur several times and may be heard as a repetitive "WHEw Whew whew" noise if the surge is mild (such as when the by-pass valve is set a little too tight) to a loud banging noise when surge is severe. Surge should be prevented at all costs because it not only slows the turbocharger wheels so that they must be spooled back up again but because it can be very damaging to the bushings or bearings and seals in the center section.

[Töuge-MR]

Nice information rotarded.

I love the GT35R.. Nice horsepower AND spool charecteristics on the 3SGTE, but thats all i know about them.