Stealth CAI The "Stealth" Cold Air Intake A 2005 Ford Focus How-To One of the most cost effective performance modifications you can add to the 2005 Ford Focus is the "Stealth" C.A.I.. 
It was tested on a DynoJet in Denver Colorado adding 6 hp and 7 ftlbs of torque at the wheels! Not bad for a $25.00 investment.

Two problems with the stock air intake system are that you cannot clean the filter and it's too long/restrictive to allow the Duratec engine to breath easily, so the "Stealth" C.A.I. was developed to solve these problems. 
The only additional part you will need is the Cone Style Air Filter itself! 

This will show you how to install your own "Stealth" Cold Air Intake. 

You will need the following tools: 
A socket wrench with a 6mm, an 8mm, and a 1/2" socket, a phillips screwdriver and a #15 Torx bit The Mass Air Flow tube has an OD of 3 1/4", a cone air filter with a 3" ID will fit but it's a VERY TIGHT fit. 
A cone filter with a 3 1/4" ID would be best, such as a K&N RX-4120. (Not the one used in this How to). 

Start by lifting the front end and putting it on jack stands for safety. 
Remove the driver's side front wheel, this step can be eliminated but access to the wheel well liner is limited, and then remove the wheel well liner. 
Remove the splash guard from under the front bumper, their are many screws. 

Loosen the 6mm hose clamp on the inlet tube above the air filter box in the wheel well and dislodge the boot from the inlet. Loosen the 6mm hose clamp on the Mass Air Flow Sensor tube and dislodge the boot attached to the stock air filter box. 

Remove the two accessible bolts holding the air filter box to the frame and pull the air filter box straight back towards the wheel removing it from the third bolt. 
The stock air filter box is mounted on rubber grommets. 
 
With two of the three blots removed the air filter box will slip off the third one which then becomes accessible. 

Remove the inlet tube above the wheel well. Loosen the hose clamp on the resonator box boot. 

Remove the two 8mm bolts holding the resonator box to the MAF tube. 
Dislodge the boot from the resonator box and pull straight up on the box to remove it. 
A pin on the bottom of the resonator box seats into a rubber grommet in the frame. 

Remove the 1/2" bolt mounting the MAF to the frame and remove the MAF tube. 
When disconnecting the MAF sensor wires pull the red slide away from the connector, and in line with the wires, to release the connector. 

Now that you have the MAF tube in your hand it's time to attach the new Cone Style Air Filter. Lightly grease the lower end of the MAF tube and slip on the pre-oiled cone filter.
Don't over tighten the hose clamps! All the parts of the intake are made of plastic; a little grease and a snug clamp are all you need to seal the joints. 

Now slide the new air filter and MAF tube back into its original location and bolt it back onto the frame. 
Lightly grease the resonator box inlet and outlet tubes and plug it into the MAF tube and throttle body boot, press it back into the rubber grommet in the frame and re-install the two bolts holding it onto the MAF tube. 

Tighten the hose clamp at the resonator/throttle body boot, again don't over tighten them. Re-install your wheel well liner, splashguard and drivers side front wheel and your done. 

Fire up the Focus and enjoy your "Stealth" C.A.I. 
 Looking from underneath the car you can see the “Stealth” CAI just above the stock splash guard on the 2005 model used here. 
Next is a look at the air path of the "Stealth" C.A.I. 
The "Stealth" C.A.I. retains the O.E.M. Resonator, Hydrocarbon Trap and Mass Air Flow Sensor. 
Looking into the O.E.M. Resonator from the Mass Air Flow Sensor tube side, you can see it’s a pretty straight open tube. The same is true from the throttle body boot side, looking into the resonator box.

The air path through the resonator box is short, clean and reasonably smooth. 
The double wall tube in the last photo is the hydrocarbon trap entrance. 
It is still a possible area to reduce turbulence by replacing the bellows style boot with a straight tube. 

We have reduced the length of the air path by several feet and opened up the intake flow allowing the engine to breath easier. 
Retaining the O.E.M. Resonator and Hydrocarbon trap provides a deep throaty sound while still maintaining some level of environmental responsibility. 

Don't forget to clean and re-oil your new air filter every 3000 - 5000 miles!! This is an over view of the whole "Stealth" C.A.I., less the throttle body boot.
This "Stealth" C.A.I. was developed by BlazingCopper_ZX3 on a 2005 D20 Duratec equipped Ford Focus ZX3.
For more information on the Stock Air Induction System see Visteon's web site.
 
 
Here are the results of the DynoJet test runs.
As you can see the first run was the best resulting in 118.5 max power and 123.4 max torque.
 
Focus Fanatic Magazine tested a stock 2.0L Duratec ZX3 in the Spring 2005 issue with a result of 112.1 max power and 115.9 max torque.
 
Based on these results the “Stealth” CAI gives you an increase of 6 whp and 7 ftlbs of torque.
 
The air filter used in this How-to cost $24.95. Divide that by 6 whp and this modification cost you $4.15 per horsepower. The least expensive per horsepower cost of any performance modification.