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      11-05-2008, 06:35 AM   #68
Second Lieutenant

Drives: Z3 M Coupe(S54) and Z4 M Coupe
Join Date: Apr 2008
Location: UK

iTrader: (0)

Originally Posted by ace996 View Post
I see your point, but not exactly...perhaps I just can't 'see' it.
If you have a straight river flowing south and you have a stream flowing into it from the east, then if the stream joins the river at an angle of less than 90 degrees, then the flow of water going south in the river will pull water from the stream into the river. Think about it, if the stream joins the river at angle of, say, 60 degrees, then there is absolutely no chance of the river back-flowing into the stream because the pressure of water upstream in the river, will force all the water in the river down the river and not into the tributary streams along its route. In the case of your air-intake, think of the river as being the air coming from the scoop in the bumper (Part 3 in the diagram of your car) and the stream being the air coming from your vent in the hood. Does this example help?

Originally Posted by ace996 View Post
EXDOS said -"I think that you will find that, under WOT, the ram effect from the two vents (parts 2 and 3 in the diagram of your M3's air intake system) will provide less air to the engine, even in a completely sealed ram air-intake system, than your OEM air intake system will do."

ACE996 said - "that's the question...they may any speed."
My S54 engine has a 3246cc engine and at the rev limit of 7600rpm, and at a Volumetric efficiency of 100% it consumes 12.33 cubic metres of air per minute. Your E90 M3 with a 3999cc engine and at the rev limit of 8400rpm and at a VE of 100% consumes 16.8 cubic metres per minute which is 36.25% more air than my S54 engine can consume. Now my air intake has just the scoop in the bumper and a secondary scoop behind the headlamp, which I see is equivalent to Parts 2 and 3 in the diagram of your air-intake.
I have done a total of seven individual mods and tweaks to my air intake and exhaust systems, all of which have individually, and collectively, helped me improve the Volumetric Efficiency at increasingly lower speeds. Now if you had to rely solely on Parts 2 and 3 to provide 16.8 cubic metres of air per minute, then I would suggest that you will not see a VE of anything near 100% until very high speeds. However, with your additional third intake, Part 1, your engine is able to obtain the necessary air to achieve 100%VE at realistic useful road speeds.

I am sure that if I were to cut a hole in my MC's hood and provide an additional intake to my air-filter box, to make my MC's air-intake system function similar to yours, that I would see a considerable improvement in VE at lower speeds in addition to those I've already achieved with my present 7 tweaks/mods.

Take a look at the photo below, it shows the rain marks on the bonnet of my car after I'd made a high-speed motorway journey (Germany). These marks clearly demonstrate the flow of air over the hood of my car. Notice how the lines seem to come closer together and concentrate in the region on the hood where your M3's hood vent is located. This concentration occurs on both left and right sides of the hood. In view of the fact that the pressure of air towards the rear of the hood is at positive pressure on a moving car, then it seems obvious to me, that your bonnet vent is perfectly positioned to provide the additional air required to supplement the air-intakes from Parts 2 and 3. I'm afraid that I just can't bring myself to cut a hole in my bonnet to allow my engine to benefit from this additional source of air, purely for aesthetic reasons.

Originally Posted by ace996 View Post
pressure sensor would do it, too
Using pressure sensors will give you the picture of what is going on inside the air-intake system, and would be extremely useful and interesting to see, but they will not give you the figures for Volumetric Efficiency. Ideally they would be part of a bigger test rig which would give you time-stamped data that could be viewed alongside air-flow measurements and rpm etc. For me, the ultimate measurement in assessing mods to air-intakes and engine performance improvements/losses is Volumetric Efficiency.

If your car is parked outside in a thunderstorm, where does the rain water go that falls into the hood vent?