More basics

Brake specific fuel consumption (BSFC) is the mass of fuel, in pounds, that is burned per hour to produce one brake horsepower. Normally this value is determined from an engine dyno since both fuel flow and engine output are measured. However based on empirical data, there is a range of BSFC that are typical of certain engine types.

For example, turbocharged engines typically see BSFC values of 0.6 to 0.65, supercharged engines 0.55 to 0.6, and naturally aspirated engines between 0.45 to 0.5. Of course, it is possible to lower BSFC (some would even say that is the goal of upgrading the engine), with competition NA engines going below 0.45... but not at full power though.

The mass of air that actually enters an engine's cylinders as compared to its theoretical maximum is called the volumetric efficiency (VE). Again, we normally measure this value instead of deriving it mathematically. It is more or less analogous to "boost pressure".

The point of all this is to get a vague idea of the VE that is necessary to achieve a targeted power level based on some simple calculations.

Let's take an Evo 9 as an example. The engine is 1997 cc or 121 cubic inches. Let's say it has a BSFC of 0.60 at peak power, and based on our real-world dyno experience it produces 320 bhp @ 6500 RPM when running an AFR of 12.5:1.

Thus, the VE is 9411 * 320 * 0.6 / (121 * 6500) = 2.297, or about 1.3 bar of boost. Pretty accurate.

Another example... the F20C of the Honda S2000. Also 2L in capacity, let's use a BSFC of 0.45... VE is then 9411 * 247 * 0.45 / (121 * 8600) = 1.00... practically 100% VE. Perfectly possible with a good flowing head.

S54 engine of the M3 CSL... 3.2L or 193.6 cubic inches. VE is thus 9411 * 360 * 0.45 / (193.6 * 7900) = 99% VE

Remember, this is not rigorous but should give a decent idea as to what's possible with what kinds of mods...