Have done a very un-scientific test over the last 6 weeks and thought I would share my opinion with you all - it may or may not help? Ran my 2.5 auto for 3 weeks with a new OEM air filter and then for 3 weeks with a K&N filter. All journeys approx same distance (mainly motorway 200-300 trips) so the conditions were about the same for both tests. I know a lot of members run diesels so obviously no idea how this would compare. Conclusion of my test: didn't find any difference in power,performace,drivability, smoothness - nothing at all - both worked equally well. I am definately not an expert and would love to be enlighhtend by someone who knows but, if the air flow is increased with these filters surely the ECU would adjust the mixture (increasing fuel supply) so I cannot understand how it's claimed they can increase fuel consumption? I found no difference in my fuel consumption between the 2 filters and although the K&N is very well made and will probably out-live the car, I cannot see that it is worth paying the extra for one. As said, this is my opinion and I am by no way anti K&N - have used their induction kits in the past and they definately work (need a good cold air supply though) Maybe I have been unfair and need to run the tests for longer? Hope I have not offended anyone who has a K&N as it could just be me that doesn't see the benefit and theirs work well?

I think you are probably right, to the extent that any improvement cannot be measured by any subjective observation by the driver, but that doesn't mean there is no change to any of the measurable parameters of the engine, although any such improvement may not be signicative.

But the fact that the filter is a lifetime one means that after two service intervals there is a financial advantage to having a K and N; also the possibility of any small tears and imperfections in paper filters could lead to increased engine wear. The solid nature of a K and N will ensure that this does not occur.

Take your point about the quality - as I said, they are very well made. As you say, the improvements may not be noticable but there's certainly no harm in having one fitted and it may be making things run better - who knows?
I think I'll keep the K&N in there anyway as they are a better quality. Thanks for your positive response.

Vandy,
I have a 2.5 auto and would be interested to know your mpg on those long runs.
Cheers,
Simon

Hi Simonm. Motorways: If I keep it at a steady 70mph I am getting about 32mpg, maybe a smidge more. If I increase this to 75-80mph it comes down to about 25mpg. If I give it some stick (use kick-down a lot) and race it I'll be down to about 20mpg! Country roads: Hard to tell but I reckon about 25mpg or a bit less? Again though, give it stick or on winding hilly roads I reckon I don't get much more than 20-22MPG? It's not the most economical car to run (that's todays understatement folks) combined with the road tax that will probably go up in the budget to £450 or so, but I still love the car. Having seen the diesel owners fuel figures it makes you wonder why we buy petrol engines really but I just don't like the noise they make - have had 2 diesel cars gefore and hated the noise (both were Mercs and this "just ain't cool")
If we keep busy earning money and we can keep pouring it all into our petrol X Trails - if we had diesels we'd only spend it on silly luxuries such as food and water!

Thanks Vandy, useful info.
I am possibly about to start commuting by car as opposed to the train as I have been doing, and I was wondering about using a K&N to try and wring a few more MPG out. I might not bother and just concentrate on driving smoothly.
I reckon on long runs by using cruise control, 2WD and minimising aircon I can get around 30mpg which isn't too bad, especially as some of the diesel guys only seem to achieve mid 30s or so.
I dread to think what I got during the heavy snow - probably mid teens for MPG but then I was enjoying myself a bit too much
Cheers,
Simon