Are there any performance hits using washable/renewable air filters?

Question

Would the use of re-usable (a la K&N) air filters, bring any performance drops?

I've heard stories from both sides of the argument.

Answer 1

I've never experienced performance drops with good renewable filters. Most engines perform slightly better with a good filter in especially the low and high RPM ranges. A bad/cheap filter is not a good choice, some have too much oil (to catch the dust) and this clogs up the AFM until eventually your "check engine" warning light turns on.

A cold/open air intake can give performance drops because of bad hose design or bad placement. Some complete CAI kits mount the air filter behind the engine. This is a bad place, because the engine will be fed warmer air with less oxygen than the outside air you want to feed to your engine.

However, when choosing a position for the open air filter you have to make sure it doesn't get wet. Wet filters don't filter very well and tiny drops of water will get in your engine with a bad effect on combustion. Also, water is not compressible so getting to much water in your engine will lead to damage.

Answer 2

I have never heard of a performance drop from using a reusable filter. You will likely see mild performance gains. Reusable filters are better flowing than their disposable counter parts.

Answer 3

It depends if you're talking a drop in filter or a cone filter. In many cases, a cone filter which replaces the airbox can suck in warm air - decreasing performance. Some cone filter designs come with their own airbox/heat shielding, or are relocated to someplace else where it sucks in cold air.

A drop in filter should not lose power per se, but make a few extra ponies (not entirely noticeable, more placebo than anything else).. on the order of 1-3% max power gain in most cases.

HOWEVER, aftermarket filters like the K&N that uses an oiled gauze is not without issues. The oil from the filter can contaminate your mass airflow sensor over time and affect your air/fuel readings leading to reduced performance.

Also, they do not quite filter as well as a paper filter.

I would say in most cases, not worth it. There are some kits for turbo charged cars (like the AEM kit for the Evolution X) that make a good amount of dyno proven power, but average return on most cars I would say is 2 to 5 peak HP. You would need to look up dyno charts for your particular application to see if there are any peak as well as "under-the-curve" power gains that would make this worthwhile.

Answer 4

On my vehicle, the twin intakes with aftermarket filters get too much airflow and cause a loss of power. This can be corrected, but depending on the limits of your ECU you may need to spend some extra $$$