I have a parts rx7 has a K&N cold air filter on it (pictured) and was wondering if it is better, or better to leave stock?

 

You won't notice any difference, so leave it stock. If anything, it'll suck in hotter air from the engine bay, so that's +2 for leaving it stock.

 

i would clean it, aside from sucking in hot air it does have that little duct aiding cold air. you can always fabricate something to isolate it from the rest of the engine bay

 

+1 on using it and fabricating some sort of isolation box to deal with hot air from the engine. Mariah makes one specifically for that K&N model, but not cheap.

Bonus, that is the CARB approved verson. You can still get a replacement CARB sticker from K&N to go with it to minimize Po Po hassles.

 

that K&N filter pictured is not cheap either!
they go for like 150 on Ebay!
see? http://www.ebay.com/itm/K-N-FIPK-Ser...item5ae59d5611

 

That is indeed a K&N filter but there is nothing "cold" nor "hot" about it, it will filter any air available.

I don't see the point of using a filter like that then using a Mariah (or any of dozens of DIY replicas) box around it...why not not just keep the stocker?

 

Better air flow as more surface area compared to stock filter size.

 

If you build a box for it, I would keep it. But if you're just going to leave it as is, I would go with the stock.

 

If it's the look you want, then go ahead, but speaking from experience here, you're not going to gain a thing from installing it. It really is more work than it's worth. I even built a heat shield around the entire intake and ran the air filter through a hole I cut to the bumper, and still couldn't notice a single bit of difference. The stock NA intake is as good as you need for a naturally aspirated rotary.

This is all butt dyno, of course. If someone posts actual dyno results, I'll shut up.

 

You may as well take off the stock intake duct too, it isn't going to do a darn thing if you aren't drawing air directly from it.

 

My own opinions:
- Performance wise, if your car is NA then leave it stock, if turbo then use the K&N filter.
- For looks or cool noise, then use the K&N filter. Yes, I do consider looks and noise legitimate reasons for modifying your car, just as long as you are not under the delusion that it makes a big performance difference.
- It may just be the picture, but that filter looks toast. They are only good for about 10 years.

 

^ Good point. If the cloth like material is missing anywhere on the filter, doesn't matter if the metal mesh is intact, the filter isn't filtering anymore.

 

Lol yea the pic was taken by my crappy phone, so it looks bad, but it is actually a pretty good filter. Anyone use flashing like used for carpentry to make a deflector around the filter? I seen something like it on a grand am once. I'll probably leave it stock, maybe play with it a bit if I ever get bored lol