lml@lancaironline.net Mailing List Archive

Bill,

Aircraft engines don't generally operate at 2 ft AGL their entire lives, so the differences in filter efficiency are not quite as important as in automotive applications. Typically space is a bigger issue, so pressure drop of the media is of great interest.

With respect to Dyno testing, if the filter area is large enough, I would not expect any change in engine power output when switching between brands. Pressure drop is strongly dependent on flow velocity through the filter, so size matters. We used to measure pressure drop across the filters in our dyno tests to ensure that we did not violate any inlet restrictions guidelines. This was to ensure we could always achieve rated engine power. Our filters were relatively high efficiency and high pressure drop as they saw the worst of all environments. These were full-time cross country vehicles used in various Middle Eastern desert environments.

In the O-360 at SL you need about 0.1 inHg drop to see a 1 hp change. That pressure drop is a measurable amount.

I am an advocate for filtering, regardless of the media used.

Chris Zavatson

N91CZ

360std

http://www.n91cz.net/

On Wednesday, January 15, 2014 1:13 PM, Bill MacLeod <macinsd@gmail.com> wrote:

You are absolutely correct about K&N filters being worthless. Worse, they lead to increased engine wear.

I have done a lot of dyno testing on Jaguar V8 engines, both supercharged and naturally aspirated, in conjunction with my avocation of developing performance parts--exhaust and intake systems for these cars.

Some of the tests involved comparing power output with standard OEM, Fram and Purolater air filters with K&N filters and no filter at all. There was no difference in power output between any of the options. Of course, these were all new filters. It is possible to show a difference when comparing a very dirty filter to a new one.

The owner of the dyno shop performing the tests told me he had done dozens of similar tests for other customers and in only one or two instances did the K&N produce additional (negligible) power. Those instances were on very large displacement truck engines and may not have had new, clean OEM type filters for the baseline tests.

Furthermore, the Jags we did use K&Ns on for up to 10K miles showed significantly increased levels of silicon (dirt) and wear metals in the oil analyses we did at 5K and 10K miles.

Not only do these filters not deliver on their hype to produce more power over regular cellulose air filters, they pass so much more dirt into the engine that wear rapidly increases soon after their installation.

I suppose their claim to additional power could be somewhat valid as the increased wear opens up the tolerances in the engine which results in less friction and thus more power. But, while this may be effective in a race engine with a very limited life cycle, it seems like an expensive way to get slightly more power from normal service engine.

Both Fram and Purolater make excellent automotive air filters. Stay away from the Fram oil filters, though. Again, based upon testing and examination of their design, construction and filter media, the Frams are pretty inferior. Purolater does make excellent oil filters. We've found others that are good as well, but these are the most widely available.

On Wed, Jan 15, 2014 at 4:56 AM, John Cooper <snopercod@comporium.net> wrote:

Bill--

Thanks for the speedy reply. I built my own airbox (see photo) because I wasn't comfortable with the unbalanced factory design although it was more compact than the one I built. In the recently posted Lancair Accident List, the 1991 fatality in Titusville, FL was caused by the aluminum flapper in the factory breaking off and lodging in the carburetor (I knew the builder.) I should say that this wasn't the fault of the factory design; The builder used too-thin aluminum for the flapper and kept flying when the engine started running roughly. Anyway, I preferred a balanced airbox design with the ram air coming in the front, and the heated air coming in the back side of the airbox. The aluminum diverter just rocks either forward or backwards and diverts the desired air up into the carb. The "unwanted" air exits the bottom.

The "air scoop" at the front of my cowling is circular and roughly 2-1/2" I.D. I moved it forward to just behind the prop. The intake expands to 4" diameter over about 12". The idea there was to slow down the ram air velocity by half to more closely match the velocity being sucked into the carburetor. The expansion tunnel on the lower cowling is connected to the airbox with a short section of 4" SCAT tube.

I have been considering the K&N cone-shaped filters to fit inside this 4" duct, but was concerned that they weren't designed to handle the high-velocity air from the ram air intake. I guess that's not a problem because the ram air has to slow down to match what the engine wants. Also, the smallest cone-shaped filter K&N makes has an opening of almost 6", and my airbox intake is 4" so I would have to cut down the K&N filter somehow to fit.

This is one area where I don't want to experiment very much.

--John

This is looking down the front of the airbox with the diverter in the ram-air position:

This is with the diverter in the carb-heat position. You can see the 2" air dump hole at the bottom. Note that the diverter is captive, and can't fall off under any circumstances.

On 1/14/2014 10:47 AM, Lancair Mailing List wrote:

Subject:
Re: [LML] [LNC2] Carburetor air intake filter?

From:
"Bill Harrelson" mailto:n5zq@verizon.net

Date:
1/14/2014 9:01 AM

To:
lml@lancaironline.net

John,

On our 320 we used the Vans RV6 airbox. This uses a large K&N automotive filter. It has a well thought out and functional carb heat feature. The downside is that it is big. Some surgery will be required on the bottom of the cowling to make it fit.

Bill Harrelson
N5ZQ 320 2,150 hrs
N6ZQ IV 450 hrs

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