QUOTE (hatchy_gt-s @ Jun 18, 2010 - 12:58 AM)
QUOTE (azian_advanced @ Jun 17, 2010 - 1:58 AM)
QUOTE (hatchy_gt-s @ Jun 16, 2010 - 10:45 PM)
Edit: If you lengthen the pipe you want to decrease the size. If your car intakes 250cfm and your original pipe is 250cfm and you increase the length without decreasing the diameter you will have say a 350cfm pipe causing drag because your intake is at a -100cfm.
cfm= cubic feet per minute
so what you're recommending is to match the volume of the original pipe with the volume of the piping in the CAI setup?
the only reason one would reduce the pipe diameter is to increase flow velocity which helps reduce heat soak from the engine, but at the cost of pressure loss.
You dont loose pressure if you lengthen and decrease diameter. If I have something that is 14in long and 3in diameter that gives me 99 cubic inches , and if I extend it to 18in with a diameter of 1 3/4in it gives me 99 cubic inches of volume. So if I have the same volume I have the same amount of pressure.
The equation for Volume is;
Pi x radius squared x hight
or Pi*r2*h
or 3.14*r2*h
The equation for pressure is;
normal force(14.7)/area=pressure
or F/A=P
or for cars 14.7/A=P
The only thing you change when you change length is distance ie the time it takes to reach the car.(I dont think you really want me to get into the math of that to)
So again, how does changing the length of the pipe change flow rate or pressure? As you just said, the only thing that changes with length is the time it takes for air entering the filter to reach the throttle body (essentially). Changing the volume of the pipe won't change anything as long as the volume change is due to length and not diameter. As air is used by the engine, the air at the intake end of the pipe will displace the air that was just used due to the fact that a gas will expand to fill its container. Thus, as long as there is always air in the intake pipe (which there is, there's no vacuum there), there will always be the same pressure for any given length of pipe of the same diameter. Volume is entirely unrelated to pressure in this case.
In a closed container, volume and pressure are inversely related, absolutely. However, an intake pipe is not a closed container, one end is open to the atmosphere, the other feeds into the throttle body of the engine. Since this is in the case of a N/A engine, the pressure inside the pipe will always be 1kPa (roughly) no matter what the pipe's volume. The flow rate is entirely related to the diameter of the pipe (for a given pipe with the same gas moving through it, A
1V
1 = A
2V
2), thus changing the diameter of the pipe will surely change the flow rate (the narrowest part of the pipe will dictate the flow rate due to the bottleneck it causes). Also, the flow rate is related to the opening of the pipe. In this case, the opening would be the air filter, which surely causes a bottleneck over having a wide-open end. Changing the length will negligibly affect the flow rate, as once the air is used by the engine, it leaves an empty space which is then filled by more air in the pipe, pushed in by the force of the atmosphere. To prove it, you could take a pump with the inlet connected to a reservoir of a given volume of fluid. You'd get different lengths of the same diameter tubing and time the time it takes for the pump to empty the first reservoir, and what you'll notice is that the time it takes will not change no matter how long the tubing is. The given volume of the fluid divided by the time is the flow rate of the pump (in the units you used before: (cu. ft.)/(min)).
I'm not trying to deny what you're saying, but I just can't wrap my head around it and am debating for the sake of my own curiosity
edit: Where does the 14.7 come from when you use 14.7/A = P? You didn't give units, but I assume you mean 14.7psi. That's entirely a false equation, because psi (lbs./sq. in.) is a unit of pressure, not force. Thus, you'd plug it into F/A=P for P, and not F.