k/n or stock air filter

[///M42 sport]

I've heard stock filters are just as good if not better than K/N. Any truth to this?

[ethree]

I've never seen any hard data but you will probably see a 50/50 difference in opinions in this thread. I run a cone filter with a heat shield, it makes a lot of noise but I've never been on a dyno so who really knows?

[nando]

it depends.. what motor do you have and is it stock? I'm seeing a 5% or more pressure drop from the stock airbox with a paper mahle filter.

[Scarlet_Pimpernel]

i have heard the same. poeple on vortex argue about it all the time. i think the only good thing about the k&n is that its re-usable. i use paper..

[jlevie]

I remember seeing an article where someone rigged up "flow bench" and tested several different filter and intake combinations. If memory serves, nothing was any better than the stock airbox and paper filter for the mass flow range of an M20 engine.

[nando]

I remember seeing an article where someone rigged up "flow bench" and tested several different filter and intake combinations. If memory serves, nothing was any better than the stock airbox and paper filter for the mass flow range of an M20 engine.

that's why I asked about his motor.. because it's definitely not the best for anything modified. It could mean 10bhp to me, which for the cost of a $50 filter isn't bad at all.

[gearheadE30]

I've got a K&N drop in in the stock airbox on an M42. Its a bit noisier, but no major gains. Maybe a little more pull at the top end, but it could have been the placebo effect. I just bought it because it is reusable and was on sale.

[Dillinger]

I remember seeing an article where someone rigged up "flow bench" and tested several different filter and intake combinations. If memory serves, nothing was any better than the stock airbox and paper filter for the mass flow range of an M20 engine.

It was all worked out a long time ago and the results caused a big stink between the guy that did the testing and the guys like BMP that were selling the first CAI systems.

[nando]

the flow difference between the filters may not have been that high, but the airbox itself can be the cause of a restriction if your engine isn't stock. i would never bother with a drop in, the paper mahle or mann filters are excellent (lots of surface area!).

[CorvallisBMW]

My understanding is that cotton gauze-oil filters actually filter better than the paper stuff, but that could have been some K&N marketing stuff. If nothing else, it can be and easier to wash and reuse a K&N rather than buying Mahle/Mann filters from specialty shops.

[Liam]

The K&N (and it's knock offs) panel filters flow air just fine, just not anymore than a clean quality paper filter (tested on a flow bench and dyno).

The stock air box (all intact) will effectively flow nearly twice as much "cold" air than a stock m20 can use (also tested on a flow bench and dyno).

My understanding is that cotton gauze-oil filters actually filter better than the paper stuff, but that could have been some K&N marketing stuff. If nothing else, it can be and easier to wash and reuse a K&N rather than buying Mahle/Mann filters from specialty shops.

That was tested as well and debunked (I think by Purolator but I'm not sure if I remember that correctly) .

[nando]

The stock air box (all intact) will effectively flow nearly twice as much "cold" air than a stock m20 can use (also tested on a flow bench and dyno).

sorry, I don't buy it. I'm not making anywhere close to twice as much HP as a stock M20, and I'm seeing 5% loss from the stock airbox. and this is still with a stock intake manifold, throttle body and not so great exhaust. I still see a ~2% loss with an open throttle above 6,000rpm (engine pulls vacuum).

[jlevie]

sorry, I don't buy it. I'm not making anywhere close to twice as much HP as a stock M20, and I'm seeing 5% loss from the stock airbox. and this is still with a stock intake manifold, throttle body and not so great exhaust. I still see a ~2% loss with an open throttle above 6,000rpm (engine pulls vacuum).

How are you measuring the loss?

A flow bench is the proper way to evaluate different intake configurations. Done correctly the max flow will sightly exceed the mass flow that the engine will require. But other factors mean that the final test is to compare the various intake configurations in a series of dyno runs all done on the same day. Those are best done on a Mustang (electrical type) dyno or similar as that type tends to be more repeatable than an inertial dyno. The "winning" intake is the one that has the greatest area under the torque curve, which may not be the one that has the highest peak horsepower

[nando]

I'm datalogging with a map sensor, measuring pressure directly, in the car as I'm going down the street. The difference is unmistakeable.

[Dillinger]

Wasn't there something about that snorkel inside of the OEM box and something about the muffler tube on some years?