Cheap and effective! The best bang for your buck is a simple 2.75" elbow off the MAF to your choice of filter.

What I described is how to modify the intake between the turbo inlet and the MAF, a more complicated change that mimics ALTA's silicone intake hose only much shorter. It allows you to mount a larger in-line filter without an elbow. I'll post pictures and results when development is finished.

 

could someone explain the point of a cold air intake on a turbo car? I thought the turbo is just going to heat it up again, then the intercooler will cool it. So wouldn't the bump in performance just be from less air restriction from the filter? since the turbo is going to heat it up anyway?

 

COOL! Yeah I want to see it! I love cheap and effective.

 

The MAF subaru uses the Denso (Also used by most modern Toyotas, and Mazdaspeed 3/6) even the new designed sensor for the 08 subies are made to go inside the intake tube and its two separate parts and on intakes the stock tube diameter is changed normaly to a bigger size to allow for more cfm's but that also changes the MAF scale that is ok to a point but after that its easly fixed with tuning. If you look at the MAF sensor for the mini cooper the sensor is part of its own tube so it does not change diameter like on subaru intakes so the scale its always the same with any intake.

 

To answer your question about the benefit of a cold air intake on a turbo car, it all has to do with air density. The denser the charge, the more oxygen can be crammed into the combustion chamber. You do this by dropping the temperature and/or increasing the pressure. There are two distinct parts of the system separated by the turbo air compressor. The fact that the air is heated up anyway as it is compressed can't be changed, but the quality of that air is what we are changing with a properly designed CAI.

There are other mechanical benefits obtained by increasing the pressure and density of the air to the centrifugal comprerssor which makes the impeller "bite" better, thereby increasing it's efficiency and outlet pressure.

Of the two variables, lower temperature or higher pressure, higher pressure has more effect on air density. This is because the change is calculated from a reference to absolute zero (-460 F) for temperature but only from 0 psi for pressure. Of course, larger differences have larger effects and the initial conditions are also important. A sample calculation: What is the % increase in air density from a 20 degree (F) drop in temperature, say from 100 to 80?

460 + 100 = 560 or 3.7%
460 + 80 = 540

What is the % change in air density from a 1 psi increase in pressure above atmospheric conditions?

14.7 + 1 = 15.7 or 6.8%
14.7 + 0 = 14.7

Hope this helps.

 

that makes sense, thanks!