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Old 05-08-2004, 01:16 AM   #1
raven_240
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how do you find the right turbo.

I did some reasearch on reading and ploting your engine on a compressor map. How ever thats only half the turbo. I dont know how to disifer the compresor side to find out the best turbo. I think all i need to know how to do is finding out what the formula to find what the shaft speed will be at any given engine speed, right?

Second thing is what is a good value for the temp on the intake. I relize this will vary depending on location and colling options on your car but does anyone know what the "normal" intake temp is on an sr20det?
This would make finding the corrected air flow much more exact.

The problem im runing into is that you plot the engines air flow requirments for a given boost and it will show you what the compressors rang is at a given engine speed, however without at least an estemated shaft speed its hard to tell what it will actualy run. Now for instance the GT28RS, acording to the map, will flow 18 psi but that takes an very high shaft speed, or the GT30R will spool to 18 psi at 4400 acording to the map but it almost needs as much shaft speed as 18 psi at 7500.

Right now im looking at the garrett GT28RS or the GT30R. Im looking to bring my HP to about 350-400 and will probably have to run 18PSI to do so. However I'm not making a drag car i whant a road car so spooling at 4500 RPM blows when coming out of those hairpin corners.

By the way im not afraid of math. So if you have formulas on this send em my way.
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Old 05-08-2004, 02:17 AM   #2
raven_240
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Re: how do you find the right turbo.

oh ya, another think i found people using a few diffrent formulas to find out what a specific engines air flow requierments are. Which one is the most acurat? Im just playing around with maps so im using the simpelist one

CFM = (L x RPM x VE x Pr)/5660

then to find lbs/min just mult my about .06....

was acurate when i maped out on the t25 compressor map for 10psi wich is what im running now.

However there is also this way:
First to calculate EVF use the following equation:
EVF=(engineCID/1728)*(rpm/2)
then we’ll use EVF to calculate the amount of air in lb/min the engine is flowing under boost and at temperature using this equation:

N=(P*EVF*29)/(10.73*T)

Where N is the airflow in lb/min, P is the absolute pressure in psi, and T is the absolute ambient temperature in Rankin.

then take n and multiply it by the VE on your engine.

If there is a better way let me know.
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