SG-Motorsport considers intake air to be any air before the throttle body. So, intake air includes Intercooler, blow off valve, intake and all other parts from the filter to the throttle body. On an N/A car, this may just be a peice of foam zip-tied to an ITB (individual throttle body), but on turbo cars this includes many parts and piping. Let's look at where the air would flow through a typical turbocharged setup.

Air Filter:

All engines, no matter whether turbo or N/A, need an air filter. When you bought your car, Nissan, Toyota, whatever, put in a cheap paper air filter. They do this for a couple of reasons. First of all, it filters really well, secondly, its cheap. Its also very easy to replace, and is disposable rather than cleanable. These paper filters filter well, however, they are very restrictive on the intake system. If the engine has to do a lot of work to suck in air, then that is less work going towards the wheels - where you want it. This is the theory behind changing the intake system on any car. By using a better flowing intake, the engine has to do less work to suck in air, and therefore performance results can be seen at the wheels or flywheel, wherever you measure from. Aftermarket companies try to master high flow, with good filtration. Certain companies lean more towards flow than filtration, but at SG we favour the Blitz LM and APEX'i Power Intake because they offer very good filtration, as well as a good power increase. Making an engine last long, rather than gaining 2-3hp is worth it to us, and we hope to you too!

Intake Piping:

Stock cars often use rubber intake piping, sometimes with ridges and very unsmooth flow characteristics. They also love to put intake air resonators everywhere to reduce intake air noise. These peices cause turbulance, or in some cases the tubing just isn't big enough, and again causes the engine to work harder than it should. By installing smooth aluminum intake piping, power gains can be found.

Another BIG problem with plastic/rubber intake piping, esspecially with older engines like the SR20DET, is the threat of cracks or rips. Even a very small hole will cause the car to run terribly (unless you are using a map sensor for fueling calculation), sometimes it will not even run at all. If you do have a crack or rip, it is very hard to track it down, and repair it. (Unless you use an SG Boost Leak Tester, of course!) For this reason alone, SG does not offer stock side mount intercoolers with plastic piping. We HIGHLY reccomend you spend the extra money and go with a front mount with metal piping. The headaches and frustrations avoided are well worth it. Not only that, but you get a nice aggresive intercooler shining out of your bumper, a colder air charge and more power - which brings us to our next point.

Intercooler:

As mentioned in the turbo section, an intercooler is neccessary for any high HP turbo car, to cool down the hot turbo charge, mainly to decrease the chance of detonation, but also to increase HP output. Intercoolers can be placed in different locations depending on the type of car, or HP goal. For example, on the mid-engine Toyota MR2 the stock intercooler is on the side, since the engine is in the rear, there can be no front mount intercooler. Even aftermarket upgrades keep the side mounting, since there is no better place. On the FC3S and WRX/STi, the intercooler is mounted above the engine, for cost reasons, and short piping to allow for quick throttle response.

There are many types of Intercooler, and for a street car you usually cannot tell a difference. Buying a kit that is mass produced for your application is usually the best bet, because the fit and finish is unmatched for the price.

Blow Off Valve:

Most turbo cars come with a stock blow off valve, and it is actually good enough until very high levels of boost. The main reason people change their BOV is so they can hear the releasing air sound when the throttle is suddenly closed. Well, we can't argue, we love the sound too (although it gets annoying quickly). A BOV works by releasing built up pressure inside the intercooler piping when the throttle plate is closed. When in boost, the turbo is spinning very fast pushing air through the charge piping. When the throttle plate closes, the turbo still pushes air, and this air runs into the throttle plate with nowhere else to go, so it compresses further. This compression causes the turbo to slow and puts a ton of stress on the shaft and the compressor itself. What happens next is called compressor surge, when the turbo is working at such a high pressure differential but flowing almost no air. This is a big no-no. You can see how this would damage the turbo over time, specifically the bearings would start to wear, and the shaft play would increase, due to the high shaft tension.

Another problem with "compressor surge" as it is called, is that when you get back onto the gas, your turbo will be slowed significantly. This means longer spool times and shortened engine response.