Ok, I had a chance to test the Coleman Xtreme against a MSR Windpro using an inverted canister tonight. I attempted to reproduce Ryan J.'s recent test as closely as possible. Here are the results:
Ambient Temp: 16 deg F
1-3 mph breeze
2300 ft Elevation
Open Country 2L pot
6" tall aluminum foil windscreen w/ .25" perforations along bottom edge
Begin with 8 fl oz seed water at 48 degrees
Boil 2L (including seed water) of water from snow
I would decant 1L of boiling water half way through and use the remaining boiling water as seed water to boil the remaining snow to produce 2L total.
Xtreme: 30 minutes using 55g (1.9 oz) fuel
Windpro: 30 minutes using 64g (2.3 oz) fuel
1) The windpro lights and runs smoothly with an inverted canister at all throttle settings. Judging by the "roar level" of the stove, there is no detectable difference between upright and inverted canister operation.
2) I did make the mistake of unscrewing the canister from the Windpro in the inverted position -- I got a nice liquid propane freezer burn on my finger. I recommend attaching/detaching the canister in the upright position.
3) By tightening or loosening the fitting on the windpro valve 180 degrees, it can be oriented so the default position is inverted. Upright operation is still possible by twisting the hose as Ryan F has shown in his pictures. Note that the twist to make the inverted hose operate upright puts less torque on the stove than the twist to make the stock upright hose operate inverted. With the hose adjusted 180 degrees from stock, the stove can be setup in either orientation without tipping an unweighted stove over. The Windpro hose is considerably more flexible than the Xtreme hose.
4) I began both tests with a partial canister and observed constant output on both stoves (again, just judging from the "roar level"). The windpro stove output finally fell off with about 10g of fuel left. I stopped the timer, and switched to another canister, relit the stove and restarted the watch. 7g of fuel remained in the first canister. I used 6g in the second canister.
5) Using an infrared thermometer, I monitored the temperatures of both stoves' canisters and valves during operation. All temperatures were within 5 deg F of ambient air temp. This suggests that the fuel did not vaporize in either stove until reaching the pre-heat tube near the burners.
6) The snow to water volume was approximately 5:1. I.e., 5L unpacked snow would melt down to 1L water.
7) My boil time for the Xtreme stove was considerably longer than Ryan J.'s recent test. Speculation....
a) I'm not as nimble as Ryan in moving the snow around -- I had to remove the lid 4-5 times per 2L boil to add snow.
b) My test elevation was 2300ft rather than the Bozeman stratosphere.
c) Snow water content varies.
d) Variation in stove output.
e) I began my test with a partial Powermax Canister.
8) As it was difficult to determine exactly how much water would be made from a given volume of snow, I actually produced 1900ml of boiling water during the Windpro test and 2050ml during the Xtreme test. The test times and fuel consumption above have been normalized as if each test had produced 2L of boiling water.
9) Both stoves were operated at maximum output. However, no "flame spillage" was observed beyond the bottom of the pot.
10) Only 1 trial was performed on each stove. Plus, I switched canisters halfway through the windpro test. So, don't jump to the conclusion that the Xtreme is 12% more fuel efficient than the Windpro. The repeatability of the experiment is unknown.