Air cleaner CFM question...

If this is correct, it will only be valid for a normally aspirated motor. Anyone know the math to come up with the equation for CFM at a given RPM for a given boost PSI????

It's still meaningless without a comparative resistance at any particular cfm. Generally the only way to decrease resistance is by decreasing the capacity to catch particles, or increasing the area of the filter media (either by making it bigger or having pleats etc). And I guess engines are designed to operate against a certain resistance, as they are with exhaust systems.

At least stock Volvo filters are generally very good, MUCH larger than those used in many cars with similarly sized engines. I don't think there's much to gain with an aftermarket filter.

I've never noticed a difference after replacing dirty filters, makes me think less resistance wouldn't be noticed either. Except if filtration is worse, dust could grind the motor out faster.

Unless a filter is severely restricted the only time flow is affected by anything other than the restriction forced on the system by the throttle plate is at wide open throttle. If you have determined that the intake air flow is insufficient to provide satisfactory performance then you will have to do some serious elargement of the throttle housing diameter coupled with intake runner improvements (both length and diameter, interior surface preparation-streamlining and proper surface finish to enhance turbulence for rapid fuel vaporization and so on). If you just want eye candy K&N is the way to go--the kits are pretty.

K&N filters have captured the fancy of many enthusiasts through clever and effective advertising. The one caveat I've found is that cleaning and oiling the filter must be done very carefully. Any excess oil that is drawn into the inlet piping will eventually deposit on the hot film or hot wire of the mass airflow sensor. Even though the burn off cycle for the sensor occurs after every shut down when the motor has exceeded about 2000 rpm it is inadequate for vaporizing the oil that lands on it, unlike the dust particles that it was designed to eliminate. This ongoing accumulation of varnish on the hot film or hot wire will cause premature, expensive failure of the part.

Bob

The K+N's do have the ability to flow more air, but that is not always a good thing. A LOT of years ago (over two decades, actually) I bought one for my BMW motorcycle. This bike has dual constant velocity carbs. The air filter flowed so mch air that the carbs would have had to be rejetted to run correctly. I went back to the stock filter and no problem.

Many of the K+Ns I have seen look smaller than the stock filter, but they pass more air, more freely? At what cost? How much more dirt do they pass as well? If you want a freer breathing motor, have it ported and polished and have a custom exhaust system made to match. If you are looking for simple, quick fixes that make more horsepower, I have a fuel line magnet that I removed from my 240 you can buy from me. Don't you think that if the manufacturers of the vehicles could squeeze more power from their vehicles with a different air filter that they would do it?

The problems you outlined are compelling enough reason to not use one on a car with an AMM.

__ __ Randy & \ \/ /alerie's \__/olvos '90 245 Estate - '93 965 Estate "Shelby" & "Kate"