How Do you read\analyse Compressor Maps
22-06-2005, 11:51 AM
#2
Professional Waffler
you plot your pressure ratio against the folw of the engine and see what efficiency band it drops into,,,, you can then work out how much extra heat is being put into your intercooler intake 
22-06-2005, 12:01 PM
#3
Professional Waffler
you need to know the flow rate of the engine too get this use
L x rpm x VE x pr
--------------------- = CFM
5660
to convert from cfm too lb/min (which most compressor maps are in multiply by 0.07)
L = engine capacity in liters
rpm = i hope you know that one
VE + volumtric efficiency
PR pressure ratio
boost +atmospheric pressure
------------------------------------ = pressure ratio,
atmospheric pressure
L x rpm x VE x pr
--------------------- = CFM
5660
to convert from cfm too lb/min (which most compressor maps are in multiply by 0.07)
L = engine capacity in liters
rpm = i hope you know that one
VE + volumtric efficiency
PR pressure ratio
boost +atmospheric pressure
------------------------------------ = pressure ratio,
atmospheric pressure
22-06-2005, 12:02 PM
#4
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From memory. Pressure ratio on the y axis, air flow on the x axis. You then have the lines representing turbo rpm and the 'island' regions relating to efficiency. If you have an idea of the bhp required and boost you want to run you can start looking at Maps. You can then see for the pressure and air flow where the turbo is operating. If it operating far from the central island you will need to change the turbo spec. There will also be a surge line.
This could mean a completely different turbo or modifications to trim, exh housing ect.
This is how I understand it, and welcome any corrections.
This could mean a completely different turbo or modifications to trim, exh housing ect.
This is how I understand it, and welcome any corrections.
22-06-2005, 12:23 PM
#7
Professional Waffler
Originally Posted by Paul Eggleton
I think between us Gareth we could write a book.
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22-06-2005, 12:45 PM
#10
Professional Waffler
the PR scale is a ratio
so work it out like i first showed
so if you was running 20 psi boost it would be
20+14.7
----------- = Pr = 2.36 pr
14.7
so work it out like i first showed
so if you was running 20 psi boost it would be
20+14.7
----------- = Pr = 2.36 pr
14.7
22-06-2005, 12:49 PM
#12
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Its a ratio, therefore doesn't have a unit. It's as Gareth pointed out above. As long as the units are the same top and bottom of the equation, i.e psi or bar. Either way you will end up with the ratio. This is what is known as a dimensionless number 
So at 2.00, the pressure coming out of the compressor is double that of what is going in.
i.e runnning 14psi will be
14psi boost + 14psi atmospheric pressure(roughly)
------------------------------------------------------------- = 2.00
14 psi atmospheric pressure
The variable is the boost. Stick different no's in and the ratio will change
So at 2.00, the pressure coming out of the compressor is double that of what is going in.
i.e runnning 14psi will be
14psi boost + 14psi atmospheric pressure(roughly)
------------------------------------------------------------- = 2.00
14 psi atmospheric pressure
The variable is the boost. Stick different no's in and the ratio will change
22-06-2005, 12:55 PM
#13
Professional Waffler
i know VE can be worked out by a fuction of HP/torque, rpm and volume,,, but my fooking head is blank,, i know ive done it before aswel,,,, dohhhhhhhhh
22-06-2005, 02:37 PM
#14
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Calculating VE
A brief explanation in simpler terms:
Also:
How to read turbo flow maps
A brief explanation in simpler terms:
VE curve is what gives the shape of the torque curve; they match exactly, so peak VE is where you get peak torque.
If you have a closed airbox with an inlet duct, VE is easily measured. You measure the velocity of the air at the inlet and multiply that by the inlet area to get volume flow. You divide that by the calculated flow (volume x rpm) to get a percentage, which is VE.
If you have a closed airbox with an inlet duct, VE is easily measured. You measure the velocity of the air at the inlet and multiply that by the inlet area to get volume flow. You divide that by the calculated flow (volume x rpm) to get a percentage, which is VE.
How to read turbo flow maps
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