I recently bought a G35 sedan and decided that I wanted to install the Z tube with K&N filter. After doing it this past week I have done more research on K&N filters and I am having second thoughts about replacing the OEM air filter.

It is a known fact that these filters are designed to be "high flow" air filters and they definitely do allow more air. With the increase in air flow there is also an increase in the amount of dirt that is allowed into the engine.

Dirt in the engine is pretty much the worst possible thing for it, and while the OEM paper filter doesnt allow the same quantity of air it definitely stops more dirt.

Also, the fact that K&N filters are oiled is also a bad thing as there are many reports of this oil damaging the MAF sensor.

These are two major concerns with using the K&N.

The purpose of creating this thread was to gather everyones opinion on the subject and to see what everyone thinks about K&N filters. Positive and Negative opinions are welcome.

 

There have been instances of oil from the filter fouling the MAF, but, as far as I know, these were cases where people re-oiled the filter themselves and went overboard. There may be other cases that I have not read about.

I also have the Z-tube/K&N filter and I'm not concerned about it. Dirt will get into your engine regardless of what filter you use. It's inevitable. I think K&N has been around long enough and have a reputation such that I can trust them.

 

dunno if this would help you, but recently there has been a small discussion about the K&N:

https://g35driver.com/forums/g35-sedan-v35-2003-06/53703-help-engine-light-went.html

i have the z-tube and K&N as well and i haven't had any problems with either of them for 30,000+ miles. like Skeleton Cru said, just don't over oil and u'll be fine

matt

 

Lots depends on how well you want engine [rings] to seal at 150-200-300,000 miles.

Most ring wear [other than bad oil type/change frequency] results from microscopic sand particles that all filters are not designed to protect against.

OEM filter does a good job against these tiny offenders [better than K&N] which blocks the bigger ones well.

Air filters per se [oem or others] are never a significant restriction to atmospheric pressure as their area [length x width -- pleat depth x # of pleats] is designed to create less than 1% pressure drop [something less than 0.147 psi or less than 4 inches of water column] at any flow the engine can sustain. Most use 1% at max rpm so impossible to read restriction at even 4400 rpm [as it would be 1/4%] at cruise it would be 1/16% at idle 1/64%. Pretty difficult to measure below 0.01 psi of restriction.

Careful about changing intake [filter box] as they are optimized to yield tiny increases in MPG at highway cruise.........the resonance points of the Helmholtz resonator from the plenum thru TB thru MAF thru filter out to atmosphere is very well designed for highway..........where every 0.01 mpg counts towards EPA number.

Sometimes upsetting this fine balance causes the MAF calibration to be off at low flows [not even counting oil on the maf element].

The MAF calibration curve [grams per second vs MAF output voltage] is recorded with all oem fixtures in place.

Errors at cruise [closed loop] can be identified by studying how much the short and long term adaptive [block learn] deviates from 100% [100% [128 binary out of 256 -exact middle] is what the average of all engines tested said the load air flow was under precise conditions. The O2 feedback loop [block learn] adjusts the injectors back to correct AF and you see how much error [from new average this takes].

A 214 cubic inch engine can only allow less than 214 cubic inches of air to flow in [from atmospheric pressure] every 2 rpms..........maybe 270 CFM at 4400 something less than 330 CFM at 6500 rpm due to the fall off in volumetric efficiency [valves and time allow less than 80% filling].

 

Q45tech, it sounds like you opened the service manual and put it in writing here. Are you saying there is really no benefit to a K&N since most filters have no real restriction relative to what an engine can "inhale" and that fine sand is the enemy that no filter will help with? I also read that the MAF sensor is sensitive and a change with the filter box may upset it as well as too much oil on K&N for example? Does this explain your tech talk?

 

Sure, your air filter itself may cause no more than a 4in/h20 pressure drop but it's the overall restriction of the air intake line that matters.

Take, for example, the testing I did on a Hyundai Tiburon. Hardly a scientific test but I hooked up a in/h20 vaccum meter to 3 points with the OEM hardware in place. On the atmospheric side of the air filter, on the engine side of the filter, and engine side of the MAF. I made 3 runs for each test and averaged the reading. Readings at wide open throttle were, in order, 15/24/30. One thing that surprised me was that the point of greatest vaccum was at redline, not the engines rated peak torque point.

When I removed the stock resonators on the atmosphere side of the filterbox, readings went to .5/9.5/23

When I replaced the stock airbox, filter and tubing with a K&N cone filter and tube connected directly to the MAF, the readings were .5 before the MAF and 7.5 after the MAF.

I went from over 1 psi of vaccum to about 1/4 psi. That is a significant change. I don't think the car was significantly faster, but throttle and engine response were significantly improved...definately a seat of the pants feel improvement. Gas milage improved slightly, about 2 mpg.

Obviously, with the amount of design and engineering that goes into cars, I can't take my Tiburon example and say that the Z-tube and K&N are an improvement for the G35. Every individual car is different. I only wish to point out that it's not ONLY the air filter that makes a difference in the flow restriction.

 

This is what I was hoping for, those are some really great and informative posts. Now I will be forced to make my own decision. Thanks guys.

 

Hey, don't stop now! I want to learn some more before I do the K&N thing. Any other opinions? I didn't think you needed to change the intake box with the K&N, or do you?

Thanks.

 

I know this is gonna make me sound like an *** but I just have to say it. WTF? It's just a filter. Slap it on there. If it worries you, Don't slap it on there. Bungee jumping is for the most part safe and fun. There are some caveats to the activity including a possibility of system failure and death. If I looked at all the facts before bungee jumping and tried to analyse it at the same level you're analyzing these filters, I'd NEVER go bungee jumping. And look at the fun I'd miss out on.

How about this: go for a couple oil intervals with the stock filter and do blackstone lab analyses for them, paying close attention to what they have to say about how well your air filter is working. Then switch to the K&N for a couple, and compare the results this next time. See if a difference is noted.

http://www.bobistheoilguy.com/airfilter/airtest1.htm

I know I'm being a killjoy but I think you're in "analysis paralysis" mode right now. Nothing bad will happen if you make the switch.

 

Oil it and install it properly and it'll be fine.
C.

 

I have installed CAI on my previous Acura CL typeS for over 50K miles. It has essentially a cone K&N filter at the end. My mileage improved and also the performance. During that time, I cleaned and oiled the filter twice. Never had any issues with dirt or oil. Just don't over oil it. Best to leave the filter on newspaper over nite just to catch any excess oil before putting it back.

 

No you don't. It's a worthwhile mod along with the Z tube. I like mine a lot on the G and had great experience with a K&N on previous vehicle - dodge dakota V8.

 

Thanks RBull. Is it worthwhile without the Z-tube?

 

http://www.knfilters.com/faq.htm#6

 

I have been using k&n's in everything I have owned for the past 20 years and have never had a problem with them. I will continue using them as they probably do make some power, and are cheaper in the long run, and they don't fill up the landfill.