Turbo compressor maps

[Dirty_SOHC]

Can any one help me understand and read compressor maps?
I have figured out the PR- Pressure Ratio and how to read the map. But I cannot seem to be able on how to calculate the corrected air flow "lbs/min". Here is a quote on honda tech, that I have cut and pasted.

Any help will be apperciated.
Thanks Rolland


quote:
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Lbs/min of air is not just dependent on CFM (as calculated based on engine displacement and speed) and temperature - you also need to multiply it by pressure ratio. Unless you're already using the pressure ratio to calculate CFM which in my opinion is misleading at best. The CFM your engine consumes at a given RPM and throttle position is fixed - the mass airflow is VERY variable.
If your engine is consuming 200 CFM of air at 112 F, at ATMOSPHERIC pressure, the mass is

200CFM *0.070318 lbs/ft^3 = 14.06 lbs/min of air

If you're boosting, say, 8 psi... it's 200*0.070318*pressure ratio

= 200 CFM * 0.070318 * (14.7+8)/14.7 = 21.7 lbs/min

- this makes a BIG difference when you're reading a compressor map since you're interested in the mass of air flowing at full boost.


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EDIT: BTW the 500 CFM was supposed to be airflow under boost...

I dont know where you're going with that..... but you just made me realize something else. If a "NEWBIE" was to read #2 airflow rate he might get confusedm cause I didn't specifically say "BOOSTED ENGINE"S CFM" I just said "ENGINE CFM". I used 500 CFM cause that is the typical CFM for a H22 with 9-12 PSI of boost. I guess I assumed that everyone would know that the 500 CFM is from a boosted engine. But I think it might be possible that someone would mistake 500 CFM for a NA engine, I'm gonna change #2 to say CFM for a boosted engine.

[Dirty_SOHC]

Here's another cut and paste I trying to make sense of to get the corrected air flow.

Quote ----------------------------------------------------------------------------

Here are a couple of formulas to use to determine which compressor to get.
PR = (boost + 14.7 + ic pressure drop) / 14.7
*1.5 is a good pressure drop estimation*

Di = (boost + 14.7) / [53.3 * 12 * (460 + intake temp)]
*130 is good estimate for post ic intake temp*

Mf = Di * displacement * (rpm/2) * volumetric efficiency
*displacement is in cubic in.; .9 is good estimate fo ve

Cmf = Mf * [sqrt(comp inlet temp/545) / (14.7/corrected comp inlet press.)]
*545 rankin is good estimate for inlet temp; Garrett uses 13.95 for corrected inlet press.*

The Cmf number is the lb/min result for x axis and the PR is the y axis. Go to this website:

http://64.225.76.178/catalog/compmaps/fig3.html

and look at the different maps until you find one that gives you 70% for whatever rpm points you are most interested in

[ninspeed]

http://www.mrcontrols.com/primers/sizing.htm This should help a bit... not for hondas, but walks you throung the
math and such

[Dirty_SOHC]

anyone know the volumetric efficiency of a 98 civic si D16Y8 engine?

[pressure_ratio]

Just use 85%,that should get you close enough

[Dirty_SOHC]

Originally posted by ninspeed
http://www.mrcontrols.com/primers/sizing.htm, This should help a bit... not for hondas, but walks you throung the math and such

Thanks Rob, but Linkie no workie

[Dirty_SOHC]

cool I think I have it now. Thanks guys:thumbsup:

[ninspeed]

fixed link

[joeo]

This is my first post here - just found this forum - looks great!
I did a write up about compressor maps that I hope you will find useful:
http://www.lovehorsepower.com/MR2_Docs/compressor_flow_maps.htm

[Primer_Drift]

Good write up Joeo, very comprehensive.:thumbsup: