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Author: Subject: Reading compressor maps
bi22le

posted on 2/12/13 at 07:49 PM Reply With Quote
Reading compressor maps

Hi all,

I have been doing my reading and research into compressors and have done a conversion spread sheet so I have my mass flow in all of the different units.

Any way, I would like some advice on 2 different things:

1) The volume effeciency dictates the multiplier for the mass flow of air goin into the engine. I have read that it depends on a number for factors but for NA engine is between 0 and 2, forced induction between 3 and 5. Any one have any more accurate data on this? In particularly 4age forced induction or modern 1.6l injection Thottle bodied forced induction engine.

2) The mass flow across the bottom of a compressor map is obviously important when reading the map. I assume that this is the mass flow when been forced, ie through the mouth of the SC. Not pure engine pre fitting of the SC. Is this correct?


Cheers.





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on_eighty_runner

posted on 3/12/13 at 08:27 AM Reply With Quote
Hi there
Volumetric efficiency is the ratio of the volume of air drawn in in our complete cycle divide by the engine size.
4 stroke engines require 2 full revolutions to complete one cycle
Eg 3000 rev/min is 50 rev/sec but 25 cycles/ sec.
For a 2 litre engine this is 50itres/second assuming 100% volumetric efficiency

If the engine is taking in 30 litre/s at its air filter it is 60% volumetric efficiency
If turbo charged you might get 70l/s through so 140% ve

When it comes to air, its temp and pressure effect it's volume so is easier to use mass flow rate rather than volume flow rate as both temp and pressure are changing within the turbo but the mass flow is constant. 40grammes/sec in is 40 g/s out.
From a measurement point of view it doesn't matter if the air is pressurised, in a vacuum, hot or cold of even where in the inlet system it is measured. Mass flowers is the same everywhere!
Steve

[Edited on 3-12-13 by on_eighty_runner]

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bi22le

posted on 3/12/13 at 12:53 PM Reply With Quote
Yup, I got all that.

I know that the VE changes the MAF by mulitiple factors. If you boost to pos 1bar thats 2 X MAF.

I was hoping somebody had readings from a boosted 4age so I knew the VE.

I know now that the VE does effect SC MAF on the compressor map.

A 1.6L engine running pos 1bar will have the same MAF as a 3.2L, all other things being considered equal.

Any other thoughts?





Track days ARE the best thing since sliced bread, until I get a supercharger that is!

Please read my ring story:
http://www.locostbuilders.co.uk/forum/13/viewthread.php?tid=139152&page=1

Me doing a sub 56sec lap around Brands Indy. I need a geo set up! http://www.youtube.com/watch?v=EHksfvIGB3I

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