How I did my ram-air intake, results
 

Now that I have good test results, I figured I would post some pictures of how I modifed Rod Bowers' ram air intake.

Rather than draw the alternate, filtered air through reed valves from the lower cowl plenum, I wanted to supply the air from the front baffle floor in the cooling air intake. This area has nearly the same ram pressure as the full ram intake, and only minor ducting losses, plus the loss through the conical K&N filter.

I made a replacement fiberglass canister that was the same dimensions as Rod's canister, then molded on the adaptor for the scat tube connection.

Rod's reed-valve canister is designed to prevent back-flow through the filter and out to the lower pressure area, loosing valuable ram-pressure. In my case, since the cooling intake area is essentially at ram pressure, there is virtually no back flow. What little back flow there is made up for by the over-size of the ram intake, able to supply much more air than the engine needs.

I get 0.5" hg lower MAP through the alternate filtered supply than the full ram air supply.
One thing that this suggests is whether the extra 0.5" hg pressure from the ram intake is worth the installation work? As I think Dan Checkoway showed, a well-designed filter mount on the baffle, followed by the standard curved intake duct, also gets within 0.5" hg of full ram pressure. This also preserves the completely clean lines on the cowl, which is nice, although I kinda like my air inlet too. But if I build another RV, I will have to decide if all this is worth it for a half inch of MAP?

here's some pic's

is it just the picture angle...
the RAM opening seems smaller than Bower's.
Does it make a difference?

Looking at the Lycoming power chart in the operators manual for my 160 HP O-320 B2B, it shows a 5 HP increase for a 1/2" MP increase.

Is it worth it?

I'm sure plenty of people would say YES! Heck, I'd bolt a mailbox to the bottom of my cowl for an additional half inch of MP!

To the OP:

What is your MP at cruise and 7500?

I bet you are getting a lot more than the equivalent of 1/2" because now you are pulling cold induction air instead of heated lower plenum air, which should be especially beneficial during takeoff.

Vic

Couldn't agree more.

It's nice work Steve, and a pretty airplane too.

Small suggestion about the hose intake; some lip radius might be a plus. Easy mod.

I like the looks of the intake! Really looks good. Almost Mustang-esque.



Gee - that paint scheme looks kind of familiar!

I have the Rod Bower set up on my rocket. I used to use the RAM air just for high altitudes and for races but after a long flight in stable air I am going to change my operations. On the way home from Pagosa Springs CO I had some time to play with systems. With the RAM air door closed my induction air comes through reed valves that surround the filter. The air is taken from the lower, warm side of the cowling, through the reed valves, the filter and into the engine. With the RAM air door open the air goes directly into the engine, unfiltered.
As we fly at 22 squared I do not really need the RAM air for MP so I elected to go with filtered air in cruise altitudes between 2500 and 8000 feet and RAM air over 8000 feet.
I had made the assumption that 22 squared would be be 22 squared regardless of the source of the air.
To test this theory in the dead calm air that we had that day I opened my RAM air valve and then reduced the MP with the throttle back to 22 ?. After letting the air speed stabilize I was surprised to note a 3 to 4 knot increase in speed. This was repeatable. As the MP seen by the engine was the same this power increase could only have been caused due to the difference in air temperature and perhaps a smoother flow of unfiltered air. After giving this some consideration it really is not that surprising as using warm induction air from the lower cowling is almost like turning on carb heat. I would not have expected this great a difference in speed for the same fuel flow so I will most certainly be using the RAM air on most cross country flights when the air is clear.
My net manifold pressure gain from using the Rod Bower system was at least 0.5? and that cost me a lot of time and money. For the kind of flying I do it was worth every penny. Now I will use it even more then before!

So far I've built two pressure recovery intakes. Both were filtered; this 390 cost more than my first house.

Airbox #1 was lovely, but in retrospect was dumb as a bag of hammers.





K&N cone filter. Way too much pressure drop on the flow bench. Lesson learned; K&N's oft-quoted equation for required filter area doesn't always apply. The filter dimensions don't help much because they make the filters with many different pleat depths. What counts is media area, not filter size....if you cut the folded media out of the rubber frame and stretched it out, how much area would you have? Most of the round or conical filters don't have much pleat depth compared to the flat plate filters. Duh on me.

I used the second airbox for a how-to example in a fiberglass thread:

http://www.vansairforce.com/communit...799#post364799

The filter was selected on the basis of media area; it was the largest thick plate filter I could stuff into the available cowl space.





Don Rivera was kind enough to run it on the flow bench. Mounted on an FM200, pressure drop through this airbox was 1.9" H20 (0.14" Hg manifold pressure) compared to the same FM200 tested with no airbox at all. I'll venture the Bower system doesn't do much better even with the butterfly wide open.

Postscript Per the data in a VAF homepage advertising announcement (11/4/09), the above filtered system is slightly less restrictive than an unfiltered Bower setup, and 10X less restrictive than a Bower in the filtered mode.

Additional experimental report.

http://www.n91cz.com/InductionSizing...izing_rev0.pdf