I just replaced the OEM air filter with a K & N. Is it ok to leave the air box cover off (which I haven't done yet) ? I have heard that the K & N "straightens" the air flow into the intake and that the more you restrict the air flow source (the small opening on the air box) the more you hinder it's performance.

 

IMO put the cover on. The K&N will probably have no difference in performance as the OEM air filter is a pretty high flow filter to begin with. All you will succeed in doing by leaving it off is to increase intake noise and possibly deteriorate your performance through heat soak.

How would it "straighten" the air flow when it pretty much is made and shaped just like the one you took off?

 

Yes you can leave the cover off. The cover helps to keep hot engine bay air from getting in the engine and muffles the intake sound, so if you don't mind the engine getting some hotter air than with the cover off, you're fine.

 

By removing air box as mentioned earlier:

You will enjoy the new engine sound very much.
You will lose efficiency in terms of mpg (Due to hotter air)
Your car will become slower and you will feel that as soon as the engine becomes hot.

But it will surely sounds great. Try it at least

 

The car doesn't become slower - actually engine heat soak with the top off seems no worse than with it on when its really hot out. Also, mpg is not effected.

What you lose without the top is that last bit of horsepower - unless you need it because you drag race all the time, you'll never notice it.

 

I couldn't tell at first if you guys were being sarcastic or not

 

keep the cover on just "gut the airbox" there are a ton of threads on this I just did it and it def. helped.

 

um, not according to my data logger.

at stop light, you'll see a big jump in intake air temp after seconds you stop, which is not noticed in the other test with the lid on.

at highway speed, the car seems to be least affected by the airbox lid off as the incoming air coming from the front at speed, i did not notice any cooler intake air with the lid off(unlike what most people think)

search for my post if you need to see some hard data, it's been posted in ht.com and here...about 3 years ago.


just keep it on

 

well, cotton glazed filter always out performs paper element filter in flow test(at expense of filtration), but i do see where you coming from.

The oem air filter looks very well design, if you ask me it looks over sized too(for a good reason). you'll get more surface area which help the engine to breath better when the filter is clogged up with dirt, most honda owner dont expect honda to put out a product that require frequent repair/parts. I believe honda use an oversized filter so the owner could get away with a 15k service period without decrease of performance.

so yes, i think a new k&N vs new oem filter would be a very very close in performance.

as to the op: go check out the under side of the lid, there's a L shaped air guide that directs incoming air from the air horn/funnel straight to the filter, most of the people gutting the air box make a mistake of taking it out(a great way to introduce turbulence)

 

What does the data logger show? Only airbox temps? Usually when people are trying to make a point, they provide the evidence themselves, not tell others to go find it, fwiw.

Having the airbox cover off doesn't effect anything to the point that you'll want it on, unless the intake noise is too loud for you. The OP asked if its okay to leave the airbox lid off, and the answer is, yes, it is fine to do so.