Unfiltered ram air...

[TravisHamblen]

I wanted to get everyones opinion, as I am fairly uneducated when it comes to this matter. I have, as my alternate air source, ram air that is unfiltered in to my IO-390 with AFP fuel injection (very similar to Dan Checkoway's setup). I do get quite a boost, but I ave been afraid to use it at low altitudes out of fear of all the dirt and junk floating around (not to mention bugs). I have used it quite a few times up over 5k+ (4k+ agl) where I fealt comfortable that the bugs weren't as prevelant and there was probably less dust/dirt floating around compared to down low.

Some people have told me I am being paranoid, that aside from dust storms or other obvious dirty air situations I will be just fine at say 1k' agl. Others have told me that I am crazy to have unfiltered ram air at any altitude.

Does anyone have an opinion, or info that they can pass along in educating me about the use of my ram air at different altitudes. By the way, I am in MN, it is well below freezing 1/2 the year with NO bugs at all, plus with all the snow and such there is no dust blowing around like other places in the US.

Travis
RV-7A 44.2 hours
Lake Elmo, MN

[rocketbob]

IMO ram air systems really just uncover an inefficient filter airbox setup. According to the formula K&N has for sizing a filter, the flat filters used for the snorkel intakes are almost 50% undersized. Next time you fly, try this: fly at some altitude and note your MP. Then climb 1000 ft. and dive back down to your initial altitude. You will find even with an additional 30+ knots of airspeed the manifold pressure stays the same. It takes a significant airspeed increase to get small amount of ram-air boost.

Many times I have flown high on cross country trips and with a clean airplane. Stop for gas and have found dust stuck to the leading edges. IMO I would work on a better filtered setup rather than going with unfiltered ram-air.

Since you live in the midwest as I do the times when air is the dirtiest at altitude is during planting and harvest, lots of dust and bugs get kicked up.

[TravisHamblen]

Originally Posted by rocketbob

IMO ram air systems really just uncover an inefficient filter airbox setup. According to the formula K&N has for sizing a filter, the flat filters used for the snorkel intakes are almost 50% undersized.

I understand what you are saying, but in my case, it is for alternate air, as in if the K&N iced over I pull the knob and I have another source of air. Albeit, I could just put a trap door on the FAB and use that, but then I would have hot air off the bottom of the engine with no ram or forced air effect. With the ram air I also have the option of getting a very nice boost if I use it under the right situations. But thanks alot for your opinion!

Anyone else, I really do want as many opinions as possible especially if you have this setup!

Travis
RV-7A 44.2 hours (ceilings at 600' today so no flying!)
Lake Elmo, MN

[Norman CYYJ]

There was a GA plane that I flew a few years back and it used an air filter for take off and landings and once in cruise you pulled a knob for ram air and no filter. I can't remember the make or model, it was an injected engine. So the manufacturer on that model that model thought it was ok. Anybody remember which aircraft that was.

[Tom Navar]

I used to routinely open the ram air controls on my Baron above 10000 msl...Then a large bug found its untimely demise when it struck my windshield at 12000 ft. Now I keep the engines filtered. The increase in MP at high altitudes was no more that 1", if that.
Tom
RV-8QB

[Chappyd]

The older Mooney's, E's & F's IO-360 200 hp have a ram air door that the pilot can open when at altitude

From Mapa's web site; http://www.mooneypilots.com/

"I did obtain cruise data with the F model with the ram air both off and on. Opening the ram air door does add about 1? manifold pressure and 10 horsepower when activated. As I mentioned in the article on the E model, the ram air idea was and still is a bad one. Mooney?s primary induction system on the early airplanes was a bad one. Loosing 1? of manifold pressure through the primary induction system is an unacceptable design and the ram air bypass is simply a bandaid for this poor design. Regardless, here are the numbers obtained with the F model in level cruise flight."

I have no opinion either way.