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Old 11-02-2001, 05:12 PM
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Join Date: Oct 2001
Location: Dallas, TX
Posts: 29
Lightbulb Here is the theoretical air intake for 300E

I've just joined this site, and it is amazing. I remember reading a post about enhancing the air intake on a 300E, where someone asked what the actual amount of air intake was on the car. Here is the theoretical amount it ** should take in**.

Let's start out at 700 RPM (low idle speed)
The displacment of the engine is just a hair under 3.0 liters, but I'll use 3.0 liters for the calculations.

Gas auto engines are four cycle engines; two up motions plus two down motions equals one cycle (4 strokes) Therefore, in 2 revolutions (2x2=4), all cylinders have gone through one cycle.
The displacement of all six cylinders is 3.0 liters. I know not all cylinders intake air at the same time, but the following calculation will work and be very very close to the more complicated solution. Taking all this into account, here goes:

(750 RPM /2) = 325 intake strokes per minute
325 intake intake strokes per minute x 3.0 liters = 975 liters of air per minute. This equates to 37.4 Cubic Feet Per Minute (Cfm)

Using that math, here are all the numbers I ran:
RPM Air Intake (Cfm)

750 37.4
1000 53.0
2000 105.9
3000 158.9
4000 211.9
5000 268.4
6000 317.8
7000 370.8
8000 423.8

Note that these are only theoretical numbers, which is based on what's called "volumetric efficiency" which is the actual amount of air the engine CAN breath in (given filter and airbox restrictions, among other factors) divided by what the engine SHOULD breath in. 98% efficiency without a filter or airbox is a high number. It is further reduced by the filter and box. I need to call 1800 for merc to see what the volumetric efficiency for the 300e is.

Note also that on super or turbo charged engines, the volumetric efficiency may be 105% or higher. In other words, the charger pushes in 5% or more air than the unasperated engine could, even theoretically. Hence, can burn more fuel, and get more power (Car computer seeks to maintain the stochiometric ratio of 14.7 parts air to 1 part fuel.)

Hope this helps; it at least shows your 500 cfm fan will work under all conditions, and will not restrict air flow when running.


Don Drake

1990 300E 125k Miles
1994 S420 100k Miles
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Old 11-02-2001, 06:02 PM
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Join Date: Sep 2001
Location: Austin, Tx
Posts: 713
hehe thanks... I didn't think anyone took me seriosly ;-) Oh well, ive yet to install the fan... maybe later, school has got me going from 3 in the morning to 11 at night... no time for anything else.

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