Woho !! I see this debatable thread has remained alive almost through a decade now i.e.- starting from June 2006 upto November 2015 !!
Now when it comes to my personal experience of the K&N Air Filter here it goes :
I had Installed the K&N Stock Replacement Filter at the Cost of Rs.5,800/= in the latter part of 2014 or in the earlier bit of 2015 on my 68 BHP TDCi (Diesel) Ford Figo ZXi immediately after the 2nd Service of my car when the Odo Reading was nearing 10,000 Kms. Did this because :
- I am naturally a spirited driver and the Figo was not exciting me enough
- The OEM Filter was not lasting enough as recommended by the manufacturer and had changed it twice in 10,000 Kms
The difference that I had felt immediately after the installation of the same then :
- The engine was and is definitely breathing much better
- The 68 BHP Engine does not go out of breath
- The engine vibrations at idling (since mine is a diesel) has drastically come down
- It has definitely added that extra punch in the acceleration giving life to the slightly under powered Figo Engine
- I do not feel I am driving the same car anymore
Here are some pictures at the time of installation :
The visual comparison of the K&N Vs the Stock Filter :
The Pack of the K&N Air Filter :
After installing the K&N Filter :
The K&N Sticker under the Hood :
My car has now clocked over 31,000 Kms in which it has done the following :
Considering the above and the 20,000 Kms run with the K&N; I would like to give the following long term feedback on the same :
- Everything mostly remains the same as before.
- However, I feel that it now gets dirty a little too quickly. Though I do not know the exact reason as to why this is happening, may be the community can give their valuable inputs.
- Since, I have retained the OEM stock filter with me which is fitted on those days when the K&N Filter is given for a cleaning (as I am not much of a DIY person), it is not much of a problem.
- My Figo's Fuel efficiency is lesser in comparison to what other Figo Owner's claim to be getting. May be I am being too much of a spirited driver which is resulting in this and I presume that the result would have been the same in case it was driven in that fashion with the OEM Stock Filter
- Another observation is that, I feel that the acceleration boost which was previously initially there in the 1st and 2nd gears is now more predominant in the 2nd and 3rd gears. I guess I am a little too observant in this

Thus, recently I decided to shift to BMC Stock Replacement Air Filter and keep the K&N as the Back Up Filter (when the BMC goes in for a cleaning) and do away with the back up OEM Filter in order to actually monitor the difference in performance between the two Performance SRFs.
Managed to get the consignment of BMC from Bangalore for my Toyota Etios GD (Diesel) and my Ford Figo Zxi (Diesel). Sharing some pictures of the BMC Stock Replacement Air Filter of my Ford Figo here :
Opened the Pack :
The Filter up close :
The BMC Pack :
The sticker reflecting the MRP & Part Number :
This was my first experience of using performance Stock Replacement Filters and I must say that it is indeed addictive. Though opinions and experiences may vary based on the car, place, usage, driving patterns, maintenance etc. which cannot be denied. I am pretty happy with using SRFs and now I am waiting to install the BMC SRF in my Figo once it's back from the workshop as it has gone in for a warranty claim of body rusting. Will share the update soon.