Well I’m a fickle person. Over the course of the past week and a half, I’ve been tinkering with my intake and diverter valve setups. I think I’ve finally settled on one; stock. I know it is quite an about face, but I’ve come to the realization that the stock setup is actually quite good and does not detract from power. It has excellent filtration, a good source of cold air, and is excellent at avoiding water intake.
The stock engine cover uses an oval maf sensor housing, one that isn’t easily duplicated in aftermarket housings. In fact, I don’t think there are any aftermarket intakes that accurately mimic the stock housing. Round intakes can come close but not 100%. The necessity of 100% accuracy is debatable but the closer you are, the better. Fujita ignored this and was rewarded with the worst performing intake for the MKV. Wholly inaccurate maf measurements and worse performance. Even certain versions of the BSH diverter valve kit threw the maf sensor readings off, not to the degree of the Fujita, but enough to reduce performance. The stock housing also contains a flow straightening screen which helps the maf read air flow as accurately as possible. In short, you do not want inaccurate maf readings.
Inaccurate maf readings can lead to a multitude of problems such as reduced performance, poor gas mileage and poor throttle response. Most of these result from messing with the short term (STFT) and long term (LTFT) fuel trims. Here is a good article from Ross-Tech explaining how fuel trims work: Fuel trim info. Basically you want to keep your trims around as close to zero as possible. STFT has a +-5% range while LTFT is +-10% I believe. I’m not so sure on the LTFT. If you exceed these ranges, your performance will begin to suffer.
With the stock intake, my STFT is less than +- 1% and the LTFT is less than +-2.5%. The aftermarket intake showed trims of -2.5% and around 5% respectively.
Stock vs. Aftermarket
The stock intake feels much better down low. Chalk it up to the MAF area design or location but I cannot deny that it feels much more responsive down low. The metal of the aftermarket intake pipe may be absorbing heat when the car isn’t moving. In the upper rpm range, the aftermarket intake feels like it pulls harder/better. It’s possible that an advantage in air speed may show up once the engine starts requesting more air. Another possibility is that the airflow in the tube becomes less turbulent as speed increases, allowing the MAF to read the mass correctly.
Filtration is one area where the OEM intake will always win. As good as the AEM filter may be, it is not going to beat the OEM cellulose filter. The stock filter also has a huge amount of surface area, with more material and pleats than the aftermarket filters.
The noise difference is not drastic between the BSH and stock intake. The BSH is already one of the quietest intakes and stock is well, stock. BSH’s intake does have a deeper growl.
Why would you want stock?
I’m not going to say that aftermarket intakes have no place. I’m just reorganizing the priorities for my car. If the stock intake can provide me with 98% of the performance of an aftermarket intake, why not? I ran an aftermarket intake for around 40,000 miles. It has certainly served me well. I just like to tinker with things. Nothing purely scientific, I know, so take my experiences for what it is. But you can be sure that the MAF area has certainly caught my eye and a lot of engineering did go into the design of the cover. I’m just deciding that they did a pretty good job.