it puts into account flow. lets say u have a long tube you will get higher in the low to higher rpms cause the velocity increases as its comming in, but if u have a short intake, i have power only in the higher rpms cause of less velocity and thus only having higher power in the upper range.
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this is from twan....
culmination origionally posted this a while back and i saved it on my computer.
i think this is the url for it
http://www.superhonda.com/forum/sho...hort+ram+vs+CAI
tuan's post
The premise of a CAI is that colder air is denser than warmer air. If you paid some attention in chemistry class you would remember that the concentration of a gas varies with temp. PV = nRT...the universal gas law.
When I mean denser, I mean that the colder air holds more oxygen molecules for a given volume. More oxygen is what supports combustion and makes power.
The general rule is for every 11 degrees F colder the air intake temperature , you gain 1% in terms of power.
What people don't realize is that the length and diameter of an intake also play a huge role on top of the temp of the air. Longer intake tubes produce more power in the lower rpms. Short ones produce a powerband that is located in the upper rpms more than the lower. Bigger diameters move the powerband to a higher rom location.
As you increase diameter, the speed of the air flow slows down but you get more air in. This is why it takes more rpms to build up enough flow speed and the reason the powerband is shifted higher with bigger diameters.
Decrease diameter and the speed of the air flow increases but the amount of air going in is less. You get a lower rpm powerband location sinc ethe speed is achieved at an earlier rom compared to the larger diameter tube.
As you increase the length of the intake tube, like on a CAI, the speed of the air flow increases: lower rpm powerband location . Shorted the length and the speed slows down and you shif the powerband up higher to a higher rpm.
So the air temp drawn in, length, diameter of the intake tube all play a role in how much power you gain and where along the rpm range.
CAI are longer. And if you compare them to a short ram with the same diameter, they make more power only in the low-mid rpms. You can prevent a short ram from sucking in warmer air in the engine bay by placing a box around the filter and place an opening inthe box that is located below or you can make a heat shield and block the heat from the engine.
We haven't even gotten into discussing velocity stacks (venturi effect), air horns, and different filters K&N, foam, metal mesh, paper)....maybe another time.
Wider slows speed: Wider has more gains at high rpms
diameter or width determines the amount of air that gets to the combustion chamber...
the wider you go, the more air you get in BUT also....the wider you go, the slower the speed of the flow....
so you have to tease out 2 ideas:
- flow quantity (amount of air gulped in)
versus
- flow velocity (how fast the air travels as it is geing gulped in)
Getting more air in makes more power. More air (flow quantity) is good BUT where is that gain going to be located along the rpm band? To answer that, we look at both length and width...this is where air speed (flow velocity) comes in: How does length and width (diameter) of the intake tube affect air speed and the location of gains on the rpm range?
Well,
Length affects only speed not the amount of air that goes in:
the longer the you go, the faster the speed.
If you build up speed faster, then the power will come on earlier along the rpm powerband. You get more low rpm power.
If the air is travelling slower, the build up of power takes longer and so the power gain happens at a later or higher rpm.
Short rams that are wide (both of these slow air speed down) have their gains in power at a higher rpm powerband.
Long CAI's tend to make more power at the lower rpms (if the width is identical to the short ram intake).
You can play around with combining different lengths and widths (diameters) to get the location of where you want your gains to be along the rpm range.
We haven't talked about long tubes with tapered widths with the biggest width being at the filter opening and the smallest width at the TB....
Tapered designs increase air speed much faster than tubes with the same width all the way thru from the filter to the TB.
So the Iceman CAI which is tapered will have a faster air speed than a constant width tube like an AEM CAI.
AEM CAI (blue) vs Short Ram with the SAME DIAMETER (red) on the same engine combination (only difference is the due to the intake):
As you can plainly see, the only place where the CAI is "superior" is at the 4000-5500 rpm range (known as the AEM hump) when you compare these on a single stage IM and using the same TB size. This is all due to the extra length on the CAI which gives superior low to mid rpm flow speeds yielding more low end power.
Notice that the short ram does quite well in comparison at the upper rpms, thank you very much AS LONG AS YOU CHOOSE THE PROPER DIAMETER. Val's Civic HX has a B20 in this test and he now runs high 12's all motor with a VTEC head, BF Goodrich drag radials , and weighing in at 2400 lb...
The cold denser air story does not translate into big gains on the dyno....I guess if you blew a fan down by the opening of the CAI to simulate what would happen if the car was moving you may see a difference but in terms of et, there appears to be no big gains there either. The dyno test using a fan has not been done. What speed would you set the fan to anyway?
The other thing you learn is that this gain at 4000-5000 rpm from the CAI is what you "feel" on the butt dyno but in terms of going fast, the gain needs to be higher at the upper rpms. So here, the AEM engineers were smart in placing the gain where you would "feel" it the most but in reality does not translate into a true performance gain on the track.....
