Quote:
Originally Posted by mfanatic325
The video was exactly what I was thinking when reading Exdos's posts. Because it seems to me that his general explanation of how he's getting such crazy power figures is due to the fact that a lot of air is being fed into the intake manifold...
And I've already noted in another thread that unless the air is pressurized, there's only so much air that an otherwise stock engine can make use of  |
Let me make a few essential points for you so you might understand this better.
To increase Torque you need to increase engine Volumetric Efficiency. Since the engine capacity is a fixed volume, the only way to increase the VE (i.e. the mass of the air/fuel charge in the cylinder) is to increase the pressure of air entering the cylinders and/or have the temperature of the charge as low as possible.
Horsepower is calculated from
Torque x RPM/ 5252. Because in that calculation the RPM is divided by the constant
5252, the point in the engine rev range at which Peak Torque occurs has a very significant effect on the HP figure which is calculated. I didn't make up that formula, so don't shoot the messenger! Try a few different calculations yourself to see how this works.
At 8000rpm the S54 engine consumes (3.246litres x 4000 =12,984 litres) = 12.984 cubic metres of air/fuel mix. Air at 20 °C and 101.325 kPa, dry air has a density of 1.2041 kg/m3, therefore, if the S54 engine at 8000rpm can be filled with air at this density, then it will consume (12.984 x 1.2041 =) 15.6340344kg/min of air (34.47lbs/min). If the air density is different, then the mass of A/F mix will be different, but the volume of 12.984 cubic metres of air will always be the same.
A vehicle travelling through air will experience an equal and opposite force from the air related to the speed at which the vehicle and the air are travelling relative to each other which will create ""ram pressure". As such, an air intake designed to capture and retain air at ram pressure can supply an engine with air at a pressure greater than ambient pressure, therefore, it is possible to achieve a greater VE than would otherwise occur if the source of air is at ambient pressure, only. The Z4M's OEM air intake is such a design.
I've previously stated that the OEM Z4M will record around 31lbs/min as Airflow through the MAF at 8000rpm in 3rd gear and since the charge at WOT is an A/F mix at around 13:1 AFR, then the actual charge is 31lbs of Air + 2.38lbs of Fuel = 33.38 lbs of A/F mix. Therefore the OEM S54 engine is operating at a VE of 96.85% at peak revs.
Since the engine is an air pump, the exhaust system must also be made more free-flowing so that exhaust gases can escape to allow the greatest cylinder filling (i.e. highest VE/torque). The Z4M's OEM ram air-intake is very good, but it can be improved by using the same scientific principles long used in other totally unrelated applications. The objective is to provide the engine with a constant supply of air at ram pressure and the graph below shows how ram pressure increases in relation to speed. Therefore, the faster the car travels the greater the pressure difference above ambient pressure is the charge, thus increasing VE/torque and shifting the peak torque to higher rpms, thus considerably increasing the HP.
