lets get some str8

lets get some str8

Adding a turbocharger does not increase the displacement of the engine. To help you understand this concept, I'll give you a short tutorial on VE (volumetric efficiency), which by definition is: Volume of air that actually enters the cylinder, in contrast to the volume of air that should theoretically enter the cylinder.

Some standalone EMS fuel tables are labeled as VE tables, but it's a different usage of the term in that form. For the remainder of this discussion, I'll refer to VE in it's true definition, which I described in the above paragraph.

Corky Bell states that a SOHC, 2 valve engine will operate around 85% VE, whereas a DOHC 4 valve engine will operate around 95% VE. However, recent testing data reveals that VE can actually exceed 100% on a N/A engine, because of engineered harmonic resonance causing a scavenging effect, and well-engineered cams with perfect valve overlap. If you wish to find a nice example of this, take a dive into the workings of the "expansion chamber" on a 2-cycle dirtbike or snowmobile engine.

Now, take the turbocharger into account. It does not increase the volume of air into an engine. It increases air density, via compression. Think in terms of an actual shop air compressor. You have a 10 gallon tank, right? Now, stuff it with 100psi of air and what do you have...a 10 gallon tank. Same concept with an engine using forced induction.

Forced induction is all about moving air in lbs/min (density), rather than CFM (volume).

Now, look a little deeper into the structure of the turbocharger. It's a restriction placed in the exhaust stream, which causes backpressure in the exhaust manifold. This backpressure results in a high pressure differential across the turbine wheel. Since pressure demands equalization, the gas passes through the turbine area and across the wheel at a higher than normal velocity, increasing as engine exhaust output increases. Now, we have a turbine wheel spooling up, which also spools the compressor wheel, thus resulting in a denser air charge being forced into the engine, forcing the cyle to repeat itself. Simple, right?

Not quite. Now that there's a restriction in the exhaust stream, the scavenging designs that would normally be used to obtain maximum VE have been negated. Conversely, the turbocharger has actually DECREASED the engine's VE.

Still yet, the air charge is much more dense than it would have been in N/A form, resulting in more combustible content in the cylinder.

Taking that into account, along with other variables, such as intake air temperature increases as a result of compression, will help understand why doubling the atmospheric pressure at the intake manifold does NOT provide double the power.

I hope this helps.

lets get some [censored] str8