Volumetric efficiency??

James Kanteraki

Registered User
I know that volumetric efficiency is around 85% for the internal combustion engine. I also know that race cars and the like can have more than 100% volumetric efficiency.

so i was wondering since our cars are super charged, this raises the volumetric efficiency right???

so what is a good estimate of the volumetric efficiency of a stock sc that makes around 12 psi???

thanks
jim
 
HI,
I'm not any expert on engines by any means, but unless your talkin about something different the internal combustion engine is not effictient. As far as i know they are anywhere from 10-20% efficient. So much energy is waisted by heat, unspent fuel and the drag of all the components like cam, alternator, water pump and everything else that needs to be turned bye the motor, that the engine ends up bein only 10% or a little more efficient. Nothing Can ever be 100% effient, i repeat nothing. That'd be like having a bouncy ball that never stops bouncing, it'd just keep bouncing to the height you dropped it at. 85% is about the effiecency of the supercharger on a 94-95 SC.

dan
 
Efficiency

Volumetric efficiency is something different entirely. How much air is consumed at a given RPM vs actual engine displacment. For example if a cylinder displaced 100 liters of air, but only sucked 85 liters per stroke, it would only be 85% efficient. Conversley, if it was force fed air under boost you could stuff it with 120 liters, then it would be 120% efficient.
 
To add a little to TransDoc's post:

A normally-aspirated engine has only atmospheric pressure, 14.7 psi, to push air into its cylinders. If the resistance to air flow remains the same but we increase the pressure by 12 psi to 26.7 psi, the engine that achieved 85% volumetric efficiency normally aspirated will probably show a supercharged volumetric efficiency of (26.7/14.7) x .85 which equals 1.54 or 154%.

Hope that clarifies things a little.

Regards,
Bob P.
 
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