Finding The Right Filtration

med_1469922028-image — The search for the best engine air filter has been debated for decades, and the battle rages on. We found evidence that this war is a long way from being over. This recent battle for the best filters came when a forum member inquired about his stovebolt Chevy engine’s filtration system.

The search for clean air isn’t always located at the tailpipe. We recently stumbled upon this thread at ChevyTalk.org where a member (krchevy) has a nicely-apportioned 1960 235ci straight-six transplanted into his ’51 Chevy. It had been blessed with headers and he recently installed a dual-carb Fenton intake to pump up the cool factor. The debate began with whether to swap out the Carters that he is currently running for a set of Rochester carbs.

As they say, that’s when the fight started. Well, not exactly. The group over at ChevyTalk.org are pretty helpful and easy-going and the consensus was that if the carbs are working, why change them. But the thread then takes a diversion, as topics often do, to what kind of filtration to plop on top of those two hard-working fuel-meters.

You can’t start a conversation about filtration on cars that were built before Lyndon B. Johnson was in office without liquid-filled filters permeating the lion’s share of the debate. The old oil-bath filter topic often brings out both proponents and prosecutors of these once prevalent sources for clean air. Many will swear that they were superior to any sort of scrubbing that today’s dry element filters could hope to achieve. Others, usually with oil on their shirts, will remember how dirty they could be if you tipped them or they slipped out of your hands and spilled oil all over the place. Remember, that oil needs occasional changing just like a dry, paper filter. But how can we know which is best for our cars?

0810160846 — Oil bath air filters have been used for decades. They work by engine vacuum drawing air through the oil inside the unit. There is no doubting their ability to add that vintage feel to a rod or custom, but they do have performance limitations.

We recently found an old paper from S. T. Mccormick, a member of the Society of Automotive Engineers (SAE) that was written in January of 1959 titled “”Air Cleaners – Dry or Oil Bath”. It can be purchased on the SAE website. Thinking that we’ve stumbled upon the holy grail, we read through the five-page report only to find an unexciting finale. The paper concluded that it depended on your application and needs. So much for finding the smoking gun.

Oil bath air cleaners work by drawing air through the oil found in the bottom of the filter housing. The air then carries some of the oil up into the wire mesh that is contained in the upper housing of the filter. This oil-coated mesh then catches any remaining debris that remained in the air flow. Keeping the proper amount of oil in the system was imperative to proper performance. Too much oil added air flow restriction and the oil could be sucked into the engine. Too little oil and the cleaner could not do its job properly.

Basically, we were forced to agree with Bel Air Kiwi on ChevyTalk.org when he described them as, “Oil bath filters are from the era of splash lubrication and should be considered as technology from that era.”

If you look at an oil bath air filter from underneath, you’ll note that there’s a pretty small opening on a fairly large filter body. The reason for this is because there needs to be a certain surface area of the oil inside the filter or else the vacuum from the engine will suck the oil up into the engine. Not helpful for plug life and REALLY bad if it were installed on a diesel engine! As engines got bigger lungs, the amount of air that they consumed increased. You’ll note that many of the later oil bath filters became more elongated or larger to help keep the oil in the filter area.

0810160848 — The underside of the assembly shows how restrictive these filters can be. As engines fed on more fuel and air, the housings grew deeper to keep the oil from being sucked into the intake.

The concept isn’t without merit though. Several of today’s filter manufacturers have realized the benefit of oil’s capability to capture minute particles and K&N has marched out into the forefront of performance filters using this age-old technology. The amount of oil is now limited, with just enough to do the job and K&N actually advises against “over-oiling” the filter, as it does not help filtration and may affect today’s sensors. Use only as much as necessary.

K&N still uses oil as a means of scrubbing air. Instead of a pool of oil, their filters have an oil-coated, pleated material that captures the particles as they try to pass through the filter. Just like the original oil bath filters, they do need occasional maintenance by cleaning and re-installing the oil.

So, what say you? Are you the type that prefers to keep an extra quart of lube on the top of your engine or do you prefer to show your bright whites? As this discussion shows, when it comes to keeping the air our engines breathe clean, we’re a pretty passionate bunch. So take a minute and share with us and our readers what you prefer and why. The debate has been going since somewhere around 1959 or earlier, so surely you’ve got an opinion on the matter!