Mini Cooper Air Filter

The amount of horsepower an engine makes is directly related to the mass air flow of the engine. Mass air flow is determined by volumetric efficiency VE, and the density (pressure-and-temperature) of the air. In turn, if you know the actual efficiency of the engine, and energy content of the fuel used, you can predict horsepower. Assume a 97.5% VE at 5400. At standard temperature and air pressure (77 degrees Fahrenheit, and 14.53 psi) this equals 22.56 lbs/hour air. Assuming 19000 BTUs per gallon of gas and a 0.33 (mechanical x thermal) efficiency this should produce 228 hp. Converting the mass flow to CFM = 309CFM. Now, add a K&N cone air filter into the picture. It may positively impact VE due to a lower air pressure drop at 309 CFM than the stock filter. Let’s say VE goes to 98%. Mini Cooper Cold Air Intake System

Based on the same calculation, the mass airflow is now 22.68 lbs/hr or230 HP. However, consider the temperature of the air. Under the hood, without any type of insulation, the temperature is probably not far from the temp of the thermostat. To be conservative, let’s say the new cone filter is breathing in 160 degree under hood air instead of 77 degree air. Using the previous formula, but adjusting the air temperature what is the mass flow rate? 19.64 lbs/hour. That amounts to 199 horsepower. Here are calcs for a couple other temps at 98% VE:

Temp

Mass Air Flow

Predicted HP

40

24.36

247

77

22.68

230

100

21.75

220

120

21.0

213

140

20.3

206

160

19.64

199

180

19.03

193

 

Which means that for every 60 degree C the density changes by 10%. Assuming the engines volumetric efficiency stays the same, then we get 10% more power out of an engine, if we can reduce the inlet air temperature by 60 degree C.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s