Recommended 912ULS Air Filter?

Kind of a general question here: Rotax says to use their oil and air filters, and their sparkplugs. How do you pick and choose which you can substitute without approval from Rotax? 

Hello Douglas

The answer depends on where you are and under what rules you fly.  If you fly as experimental in most countries you can do what you want without regard to what Rotax says.  I personally feel that is not what someone should do and you will get a lot of other opinions mostly based on speculation and not real testing or evaluation.  If you fly a part 23 aircraft, SLSA or VLA aircraft you need to check the rules where you are.  Some authorities will state you must use only the parts called out by the manufacturer.  (of the aircraft normally)  If an OEM, manufacturer, states follow the Rotax guidelines and simply passes that on then normally those categories follow the Rotax parts lists.  

I see that you are in the USA so check your certificate of airworthiness for what your craft is registered under.  Take it from there. 

Cheers

Just food for thought during your considerations;

After testing some paper filters and K&N filters I now prefer K&N. Decades ago K&N used to claim they had better air flow. I thought that was just a marketing incentive. After testing several paper filters against the K&N I found out they were right. For instance. I had a client that had a Rans Coyote and his EGT's were always too high and he always had to throttle back to reduce the EGT temps. So I took out the paper filter and replaced it with a K&N and his EGT temps dropped 150F across the board. I have since seen this on other aircraft too. 

Plus the K&N should last for many years unless you damage it with a strong solvent like gasoline or something similar. Plus people want to over oil them and then the oil gets sucked into the carbs and can make a mess and or cut down the air flow.

Hi RW,

With all the different SLSA I work on I haven't found any of the Mfg's objecting to switching from let's say a paper filter to a K&N. There maybe some, but I haven't run into on yet.

That said it never hurts to call the MFG and ask about things before you do them.

Hi Roger,

Interesting observation;

"For instance. I had a client that had a Rans Coyote and his EGT's were always too high and he always had to throttle back to reduce the EGT temps. So I took out the paper filter and replaced it with a K&N and his EGT temps dropped 150F across the board. I have since seen this on other aircraft too."

In my limited understanding, high EGT's may be as the result of too lean a fuel:air mixture .

If the above is correct, the K&N filter, in your example, has restricted air flow resulting a richer (cooling) mixture, reflected in the lower EGT. 

This would then contradict the K&N assertion that their air filters deliver a better airflow.

What say you?😈