# Volumetric Effieciency.

**URL:** <https://forums.speedlife.net/t/volumetric-effieciency/248226>\
**Category:** Shift518 Automotive\
**Created:** [November 8, 2009, 9:52pm UTC](https://forums.speedlife.net/t/volumetric-effieciency/248226 "2009-11-08T21:52:08Z")\
**Posts on this page:** 1\
**Showing post:** 5

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**Author:** ![99FRC](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/99frc/32/6335_2.png) [@99FRC](https://forums.speedlife.net/u/99FRC)\
**Post date:** [November 10, 2009, 7:09am UTC](https://forums.speedlife.net/t/volumetric-effieciency/248226/5 "2009-11-10T07:09:40Z")

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> [@Well, somebody had to do it......](https://forums.speedlife.net/t/well-somebody-had-to-do-it/25481/128):
>
> Volumetric efficiency is just the percentage of air that is filling your cylinder at a specific speed/load condition vs. the volume of the cylinder.
> 
> At zero rpm if you opened the intake valve the cylinder would fill.
> 
> As engine speed increases the air needs to flow so quickly that the viscosity of the air limits the amount of flow. You don’t get all the air into the cylinder as you could have if you gave it more time.
> 
> Simple as that.
> 
> Its mostly shear stress, and throttling losses.
> 
> Solution: bigger ports, bigger valves. Don’t restrict the airflow.
> 
> You maximize volumetric efficiency my minimizing air velocity. Of course this makes a shitty engine which is only good for top end, or a really sweet diesel.
> 
> Turbocharging can really help maintain a good Ev by increasing density, and therefore reducing velocity.

Is this why a Cam is beneficial? Leaves the valves/ports open for a longer period of time?

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