Originally Posted by Decipher
Some intakes are acceptable to run without a tune, such as the K&N. That intake doesn't change the diameter, therefore flow dynamics are unchanged, meaning no tune is required.
It doesn't matter if the diameter is the same. The flow pattern is different, which throws off the MAF scaling.
ALL intakes for the 08+ WRX/STi need a tune...ALL of them, there are no exceptions. None of them measure close enough to stock to work with the stock scaling.