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Originally Posted by brandonloos_21
I ended up ordering an upper silicone inlet pipe as well as an afm drop in. From what I'm reading, keeping the stock box is good, and the drop in adds some responsiveness and noise. I'm addition, I figured for the low price that I would do the silicone upper inlet pipe (which deletes the resonator). Is this the "best" intake combo for these b58's (stock turbo). In addition, do the lower turbo inlet pipes prove to be effective? Thanks
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Some of the comments on this thread may be incorrect because they are beginning with an incorrect assumption. The incorrect premise is that if an aftermarket drop-in filter is allowing more air into the engine that it must be allowing more harmful particulates to pass through as well.
But what if that's not the case? What if the reason that the stock filter is blocking more air is because it's made as cheaply as possible out of materials that are less than the best for the application?
What if a company such as aFe or K&N that specializes in high tech air filters, designs a drop-in filter that uses a high tech material that blocks the same particulates as the stock filter while also letting more air through?
So don't assume that an aftermarket airfilter might let more particulates into your engine. You can just as easily assume that the stock airfilter just sucks, and it is blocking too much air needlessly.
Don't fall for the fear factor opinions either. These companies have scientists and engineers who specialize in airflow and have the laboratories to design & test their products. They aren't going to risk millions in lawsuits.
A good drop-in filter can definitely add more performance by increasing the airflow since it's less restrictive than a cheap stock airfilter. How much is debatable. It's not a lot, somewhere in the range of less than 5%. (5% of a 300hp engine is 15hp.) Most people's butt dynos perceive a higher responsiveness from a high quality drop-in filter.
As for intakes, they add some additional variables. Think of an intake as having two goals: performance and sound! First let's discuss how an intake can provide better performance.
Most guys assume that since intakes have bigger air openings that the performance must be greater because more air is going in. Actually the purpose of the big openings is to let more sound out!
The reason that an intake may create more performance is the exact same reason that a high flow drop-in filter adds more performance. The intake is getting rid of the restrictive cheap stock airfilter and replacing it with a higher performance airfilter.
Typically a drop-in filter will have the same outer dimensions as the stock airfilter. It can only change the filter material and possibly the number and size of the pleats to increase filtering surface area. An intake can modify both of those but it can also change the actual size of the filter outside dimensions as well.
Many aftermarket intakes use a cone shaped airfilter which is very common in all kinds of performance engines. The cone provides the potential for much more filter surface area. For instance I have measured BMW drop-ins vs an MST intake's cone filter. Just in outside dimension the cone filter has 15% more surface area.
But if one looks closer the MST filter also has many more pleats than the drop in filters. To get an exact surface area comparison would take cutting apart two perfectly good are filters to flatten out and measure the filter surface area. But just by doing a visual is obvious that the cone filter has a clear surface area advantage.
So an intake with a cone filter (assuming the same or better filter material) should be more efficient than a stock filter or a drop in airfilter.
Back to the sound goal of an intake. I mentioned that an intake has larger openings than a stock airfilter box to allow more of that turbo spool sound out. If an intake is well designed then it can do that. It can have a great sound that many people desire. But there are two intake design criteria that can degrade performance.
The first intake design criteria is whether an intake is considered a closed box design or an open box design. That's really a misnomer because they are all open box designs because they have to have a hole or holes to allow air to enter to feed the engine. Usually an intake is considered to be closed if it has a top lid on it.
The assumption is that heat rises so if an intake doesn't have a lid then it could be pulling in the hottest air under the hood. Hotter ambient air to start can cause an engine to have a power robbing Heat Soak condition faster. Everyone pretty much accepts this premise because someone would have to hook up a lot of temperature sensors all around the intake box area and do a heck of a lot of testing to prove/disprove it. So generally people assume that if an intake has a lid, it's a closed box so it must be better than an intake without a lid.
The second intake design criteria is the one that creates the most performance problems for various intakes. It is the environment around the MAF sensor that is located in the intake piping immediately after the air leaves the airfilter. The MAF sensor feeds airflow measurements to the cars ECU telling it how much air has gone through the airfilter and is headed towards the turbo. BMW engineers have finely tuned the algorithms based on the size and shape of the stock air tube at the MAF location as well as the placement and depth of the MAF sensor into the air tube itself.
Quite a few aftermarket intakes dramatically change these factors so that the readings from the MAF sensor may not calculate the same way. The values are not longer optimal and accurate so the intake can cause engine performance to suffer.
I often read people who are intent on more intake noise choosing an intake that they heard is loud and cheap. They need to also read about performance issues to see if others have reported error messages, sluggish performance, etc.
I've heard consistently good things from friends about MST Intakes. And I've been using an aFe Pro Dry drop-in airfilter for several years now. I'm doing some dyno engine testing in Nov/Dec. I'm hoping to have enough time to collect some performance numbers on a couple of intakes and a couple of drop-in airfilters. I'll post the data.
Hope this helps!