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      11-05-2008, 05:10 PM   #77
exdos
Second Lieutenant
 
Drives: Z3 M Coupe(S54) and Z4 M Coupe
Join Date: Apr 2008
Location: UK

Posts: 221
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Quote:
Originally Posted by ace996 View Post
So you plugged a leak in your intake system and made your ram-effect more efficient...that's what I would like to do. Increasing the amount of air that is forced into the box is not going to make as much of a difference if there is a hole in it. It's like filling that tub with two drains(air manifold and the hood vent)...block one and the water will fill up faster, just like it did when you blocked the brake-duct exit.
No, you're wrong. The MC's OEM air intake doesn't have the leak you are suggesting. The OEM brake duct on my MC is NOT actually a scoop for the air intake system, it merely acts as a source of cold air into which the snorkel from the air-filter box is attached. However, I have converted it into a scoop for the air-intake system by almost completely blocking it off, this has increased the pressure inside the "scoop" over what it was when it was a "brake duct". The second air intake is behind the headlamp and this is VERY leaky and is not sealed at all. If you block the mouth of this second air intake, then the MC loses power BIG TIME at WOT.

The photo below shows what I have done.



It appears to me that you have the idea that some of the air entering your intake system through the air scoop, Part 3, when the engine is working at WOT will exit out through the air intake/vent Part 1. This just won't happen. Even if the engine is operating at a VE of, say, 110%, the pressure inside the air intake system just in front of the throttle isn't going to be at a static pressure of much above ambient air pressure, but for your engine to be operating at a VE of more than 100%, then that will only occur due to ram effect as a consequence of your car moving at sufficient forwards velocity to produce a sufficiently high positive dynamic pressure at the openings of Parts 1,2 and 3. Your engine, being an air pump, will always be at the lowest pressure point relative to the pressures at the openings of Parts 1,2 and 3 when the engine is working at WOT. Yes, the air pressure above Part 1 will be lower than Parts 2 and 3, but at WOT it will always be above the pressure immediately in front of the throttles. Remember your engine is a normally aspirating (= sucking) air pump and this creates relative negative pressure to draw air inside it.

Think about this: if your bath taps had hose pipes connected to them so that the water leaving the hose pipes was below the level of the overflow drain in the bath, do you think that the water would stop flowing out of the pipes as soon as the water level covered the ends of the hose pipes and that this would stop the bath from filling further? If not, why does this arrangement not stop the taps from running, even if the hot tap was only flowing at half the rate as the cold tap?
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