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# Volumetric Efficiency

### Tech Articles

Discussion and questions related to the course EFI Tuning Fundamentals

Hi,

I have a 2011 MK6 GTI CCZB with a 82.5mm & 92.8mm bore and stroke. Based on my calculation I arrived at 496cc per cylinder.

If I'm not wrong with my numbers, the volume of my cylinder should be 52.5 ft^3/min or 29g/s at 6,0000rpm. My question is, whether Mass Air Flow can be used to calculate engine efficiency for a force induction engine? I logged 300g/s and that makes about 75g/s per cylinder. That would mean my Volumetric efficiency is 250%?

I really, REALLY dislike the use of "volumetric efficiency" in this context, preferring to reserve that for the internal efficiency of the engine, and would use the term "mass efficiency" - but as I'm in a minority (of one?), then yes, if your math' is correct (you mixed different measurement systems).

Indeed, VE is very strange term. I also don't like it...

Yay! Doubled our minority overnight :-)

I think, to calculate 'Volumetric Efficiency' in this context, you would need to divide the Mass Flow with the Pressure Ratio first, then further divide that with the geometric cylinder swept volume.

So for instance if your MAP sensor was reading 220 kPa, and the Barometric Pressure at that time was 100 kPa, your Pressure Ratio is 2.2.

Your 'Volumetric Efficiency' in a conventional sense would then be around 114% at that engine operating point.

Volumetric Efficiency is very tricky subject. It represents how well the cylinder is fed with fresh air fuel mixture. Although intake manifold pressure has direct correlation with cylinder filling it doesn't tell you how good your hardware works ( head, camshafts, valves, manifold, runners) with consuming air avalable at intake manifold. Moreover, it shows you that air flow isn't optimal since air is kind of stuck at intake manifold creating boost...

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