exhaust ramps, lips

[kmwoody]

Has anyone experimented with the exhaust outlet ramps or lips on a 3300 exhaust? Sonex recommends 30 degrees and 1 inch length, would 40 degrees draw more air out or would 40 degrees just add more turbulence and or drag. The ramps sent with the baffle kit are closer to 1 1/4 inch.

Ken W
Sonex 959

[WaiexN143NM]

Hi ken,
Interesting question, would be interested too to see if any one has experimented with the lips. We opened up our exit hole size on the ramps. Have also wondered about the exit exhaust stacks , cutting them parallel to airplane.

WaiexN143NM
Michael Radtke

[peter anson]

I pretty much ignored the Sonex plans on this. The Jabiru installation manual calls for outlets to be at least 3 times the size of all the inlets, so I just made them as big as would fit and put pretty large lips on them as well. If you go about 3/4 of the way down http://sonexaus.wikispaces.com/Peter+Anson+-+Sonex+894 there are a couple of photos. It cools well enough that I have since reduced the angle of the lips. I might be wrong on this but I'm fairly convinced that the only reason people have trouble with Jab 3300s running too hot is that their air outlets are too small. My early model engine, Serial 33A-116, with thick fin heads runs CHTs of around 125 C on warm days.

Peter
Sonex 894
Jab 3300
231 hours

[DCASonex]

Sonex cowl vents worked for me with both the Jabiru and current CAE 3300 engines, however, must be fanatical about sealing any air leaks so that ALL incoming air to cylinders and oil cooler passes through those to pick up heat. Any air that bypasses just adds to air that must exit cowl which reduces pressure differential across cooling surfaces. Top left engine mount on Jabiru or CAE engines is a challenge to properly seal. If anyone interested, e-mail me, I have some photos or mine.

David A. Sonex TD, CAE 3300

[kmwoody]

Thanks for the replies.

I am sealing the baffles tight, I want all the air cooling the cylinders. I decided to stay with the recommended 47-50 sq in outlet to start, I figured I could enlarge later, if needed. I cut the exhaust openings per the installation manual, but when installed I came up with 46 sq in, excluding the 4 sq in I need for the exhaust pipes. I plan on cutting back the aluminum tunnels until I reach the 54 sq in needed. Approx. 1/2 inch off of each should be enough. I don't want to cut off so much that I get back pressure into the cowl. Thats why I was planning on 40 degrees instead on 30 on the lips. I am not an engineer so that might not make sense.

Ken Woodraska
Sonex 959
Slowly installing a CAMit 3300