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Volumetric Efficiency
You dumb hicks gotta learn something metric, ha!

So the amount of power your motor makes is an indication of how much air it flows through
itself. To get straight to the point, a two liter engine operating at 100% volumetric efficiency
(VE) will fill its cylinders with a full two liters worth of air during each cycle. A .5 liter cylinder,
then, will be filled with exactly .5 liters worth of air at 14.7psi. The pressure in the cylinder will
be exactly the same as the pressure in the atmosphere.
  The way turbos and superchargers work, far more than 100% VE is possible. Because they
compress the air, you can have a higher air density; essentially more energy in the same space.
Because of this, a .5 liter cylinder can contain 1 liter of air; in .5 liters worth of space because it is
compressed. If the air was the same temperature as uncompressed, it’d make twice the power.
Twice the air = twice the power.
  We run into a couple problems which limit this: High pressures in the cylinder at a certain
point become too high to keep from spontaneously combusting, which, frankly, isn’t very
spontaneous at all. It’s called detonation, which I’ll go into in another article. But essentially,
the compressed air goes kaboom before the spark plug tells it too, and your engine will likely
break in to eleventy billion pieces, though I’ve seen them go into thirteen gazillion pieces as
well, in extreme cases. So basically, you can’t compress the air too much or it will just combust
on its own.
  The second problem we run into is that as pressure goes up, so does temperature. This not
only makes less power, but makes it more likely to detonate (see above, idiot), because hot air is
less resistant to detonation.
  Thirdly, a 2.0 liter motor has a hard time physically flowing 4 liters worth of air, if you double
the pressure. “Pumping losses” mean that it is difficult for more air to get into the cylinders, and
the more pressure you pump into the engine, the harder it is for the engine to swallow the air
without restricting it. So blasting tons of boost out of a turbo into a motor that can’t take it will
back up pressure in the intake manifold. An exhaust that won’t flow the air out will build up
enormous air pressure in the cylinder. This will also lead to detonation.
  So what do we need to get out of this? Volumetric efficiency is the ability for an engine to
breath. Blasting more boost into an engine that can’t flow well the extra air wont’ do much
good. If the engine can’t flow the air through it, it won’t make power but boost pressures will
be sky high. This is exactly why you can NEVER compare power levels at certain boost levels. If
the engine can flow a lot of air efficiently, it will make a lot of power at a low boost pressure.
Running 20psi is hardly impressive if the engine can’t flow much air through; as a restrictive
engine will make for high boost pressure and low power. Think about blowing air through a
straw; if you blow lightly, a good and efficient motor will be easy to blow through, like a straw
for a slurpy at seven eleven. A crappy motor will be like blowing through a coffee straw: you
will build up a lot of pressure in your mouth but not much air will be going through the straw.
You are a high boost straw that makes shit for power.
  Don’t compare boost level’s, it’s useless. Leave that to Honda-Tech and all their nutswinging
fanboism.