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EFI Tuning Fundamentals

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So VE can be increased with forced induction ?

Hello Dean

Volumetric efficiency can be improved in a number of ways, most effectively this can be achieved by compressing the induction charge (forced induction) or by aggressive cam phasing in naturally aspirated engines as seen in racing applications. In the case of forced induction volumetric efficiency can exceed 100%.

People seem to use that term but I REALLY hate it being used like that - I'd call it something like Mass Efficiency or, better yet, Mass Ratio.

Why? Because traditionally the VE is the actual Vs nominal volume of charge in the cylinder. Heck, when you consider adiabatic losses, it can be considered LESS efficient.

Why is this important? Because using higher boost pressures to increase the mass of air in the cylinder, rather than improving the actual air flow through the intake system, increases compressive temperatures which requires improved charge cooling and greater pumping losses, and forcing the air through the 'charger requires more power to overcome the inlet pressure.

Think of it this way - you have a windmill (bear with me) and you want to grind more corn. You can do this by putting larger sails on it, or reducing the friction in the various bearings so the original sails have more power left over for the milling. Both mean more corn will be ground.

The first isn't increasing the efficiency, but the second is.

Should one wish to discuss this further, I'll come back to it - but I would suggest considering the relative densities of the air in the plenum Vs in the cylinder.