Problem with K&N Filters: ref:
http://www.mz3.net/articles/149.html As delivered from BMW the M44 engine in the Z3s really is not as rev happy as say the engine in a Miata. Above 5000 rpm the power feels like it has reached a plateau and there isn't much more to be gained by revving the engine higher. The reason for this is because up high your engine's ability to breathe is being restricted. I wanted to see if I could correct this and verify an improvement.
After looking into the intake systems that were on the market or known to be 'in the works,' I determined that there was nothing out there that I would put on my car. The following are a few of the setups I found and some of my reasons for rejecting them:
Drop in K&N filter ($40): in my opinion, K&N filters do not filter as well as your stock paper filter. I will not put one on my car. Your filter is the first and only line of defense against letting dirt into your engine. The K&N is made from an oiled cotton gauze, if the oil dries out the 'filter' basically stops all filtering. I have heard it said that when a K&N filter gets wet the water can 'wash' the previously filtered dirt right through it and into your engine. The person who told me this raced motorcycles and said that when he switched from K&Ns back to paper filters his engines lasted much longer between rebuilds. Lastly, Greg Hudson had performed dyno tests comparing a new stock paper filter against a new drop in K&N filter... the result was a LOSS of power with the K&N. That demonstrates that the paper filter isn't what is limiting airflow as the paper filter has a huge amount of surface area for the size of our engine. Swapping filters does nothing to address the real source of restriction in your intake.
K&N Filtercharger cone filter ($149): Has a lot of problems. It has the same filtering concerns as the drop in filter and the rest of the setup adds a few more problems. The cone filter can suck in hot radiator air which will hurt performance. This is because cooler air is denser air (heavier), the more air weight you can get into your engine the more fuel will be injected and the more power you will get out of your engine. The circular shield that some sell might help a little but it will also increase restriction as it blocks the filter somewhat. It still doesn't get all that great of a source of cold air either. As with most other cone setups the tube that connects the filter to the HFM changes diameter at the cone filter and at the HFM. Those 'adapters' are not a good idea. When they increase or decrease in size it will cause turbulence and restrictions in the airflow. For the HFM to meter the air weight properly it needs a smooth flow of air through it. The connecting tube changes size right at the start of the HFM, this could cause turbulence which would result in improper metering by the HFM. If the HFM isn't able to properly measure the airflow into the engine the DME is going to be injecting the wrong amount of fuel. This will keep the engine from running optimally and won't be making the power it should. Additionally, the filter is right in front of the HFM and the airflow doesn't have much space to 'settle down' so it will still be turbulent from passing through the filter itself when it hits the HFM. There will be more on this later.
Art of ROAR cone filter (~$200): Mostly the same problems as the K&N setup above.
ECIS (~$200, when available): Uses a K&N cone filter so it has all the same filtering concerns and most of the other problems except it has a shield behind/besides the filter to block off the filter from the rest of the engine compartment to help with the heat problems.
Dinan Cold air intake ($299): uses a K&N cone filter so it has all the same filtering concerns. It positions the filter behind your foglight to avoid the hot engine air problem but exposes it to more water. Has the same type of 'adapters' and the problems they can cause that all the above cone filter setups share.
What I was looking for was a setup that kept the paper filter (they filter well.. even when wet) that had a smooth airflow to the HFM for proper metering, and had a good source of cold air but that allowed the engine to breathe better.
Linear Mode
