I guess this is a subject that has been explored in the past. However, I can not see why my mileage on my '13 RTs is 27 MPG at best. I have gotten the ole "it is a high performance engine", and the "that is just what it is" statements.
Here is what I got, and what I think may be going on to contribute to the low mileage.
I put a 2 Brothers exhaust with the hope this may help my mileage, it did took me from 25.5 to 27 city/highway.
Upgraded the plug wire to ACCEL and the plugs to NGK Iridium, no help on mileage. Nitrogen gas in tires. Front 24 lbs. Rear 28.5 lbs. Kendra up front and the New Arachnid compound in the rear.
When I was putting the exhaust on I noticed the location of the Cat converter, how close it was to the bottom of the fuel tank.
Did some reading and found out that a CAT runs at about 800 degrees F. I assume this temp is reached by keeping the exhaust moving around in the Cat and increasing back pressure. Any way the temp of the Cat is not the critical factor here, but the location.
I could not get the thought out of my head that I had in effect a HOT PLATE under my gas tank. I am thinking that if the heat from the Cat is warming the gas inside, and as the gas gets warmer it expands. That as the gas heats, expands the computer controlled injectors add more fuel to the engine to make up for the lost density of the gas. So to validate this "theory" I bought a probe thermometer. It has the sensor at the end and approx. 24 inches of steel cable that allowed me to put the sensor directly into the fuel tank. My results from 2 tests were:
Test one, 50 mile run with 2 shot stops and a 30min stop for lunch. Be fore engine start up after a rather cool S. FL. night (65 degrees) Ambient temp of air 76 degrees F. Temp of fuel 74 degrees. Placing probe in gas and Velcro the read out near the glove box, the wife and I headed out.
Warm up approx. 5 min., Fuel temp no change, 2 Miles to gas station, shut off, went in for bottled water, smokes, and a candy bar for the wife.
Approx. 10 min before restart. Fuel temp 80 degrees. The fuel had warmed up as it was sitting after approx. 10 min. of engine run time.
Left Homestead Fl for a 22 mile run to Key Largo, ambient air temp at this time was 78. Fuel 80. Got on US 1 and was running approx. 55-65 miles an hour. After just a few min, the fuel was heating up. Approx 2 degrees in 3 min. Approx 30 min. latter when we stopped for lunch at Key Largo the fuel temp was 116 degrees....THE TEMP of the fuel was going up as the bike was moving!
pps: This surprized the heck out of me. Lunch took approx. 30 min. Before start up for the trip home the fuel tem was 118 degrees. Again the temp went up as the bike was off. One the return ride the fuel temp seem to level off at 125 degrees :yikes:. With ambient air temp at 78, on a moving bike. When I returned home and after bike sit for 30 min. The fuel temp was 120 degrees. After sitting one hour the temp was 99 degrees.
What I learned was the CAT does in fact act as a hot plate under the fuel tank. That the fuel will heat up when the bike sits after running. That the fuel temp goes up as the bike is moving at normal highway speeds. Total time for the this test was a tad over 2 hours, the total running time of the bike was 1 hour 10 min.
The second test was much shorter. Cold bike ambient air temp 81 degrees, fuel temp 74 degrees. Again bike was sitting all night and night low tem was 68 degrees. Start bike, warm up approx. 5 min. 2 mile city traffic to our favourite breakfast place. Total run time less then 20 min. speed not over 25 mph. Fuel temp on shutting down 99 degrees. 45 min. for breakfast. fuel tem 85 degrees. Run time home less then 15 min. Fuel temp 107 degrees. Shut down bike and 30 min. latter fuel temp was 98 degrees.
What I learned here was the fuel temp goes up rather fast, and down rather slow.
I have not down a test a full one highway speeds of 65-75 mph for any extended time. Truth be told, I do not know if I want to know fuel temp after 3-4 hours of riding......
2 Questions I need some input on: 1) I know gas does expand when it gets hot, are the temps I recorded high enough to cause expansion to the point it could affect gas mileage? 2) I know that the back pressure from the Cat may effect gas mileage, but to what degree I have not a clue.
My plan now is to get a Cat bypass pipe. I am looking at near $300 to purchase and I would assume another $100 or so to install. Is there anyone who has put a Cat bypass pipe on their 996 Rotax and saw an improvement in gas mileage?
Rather long post, but wanted you to have the background on what I did etc.
Thanks a bunch,
Doom
:doorag:
Here is what I got, and what I think may be going on to contribute to the low mileage.
I put a 2 Brothers exhaust with the hope this may help my mileage, it did took me from 25.5 to 27 city/highway.
Upgraded the plug wire to ACCEL and the plugs to NGK Iridium, no help on mileage. Nitrogen gas in tires. Front 24 lbs. Rear 28.5 lbs. Kendra up front and the New Arachnid compound in the rear.
When I was putting the exhaust on I noticed the location of the Cat converter, how close it was to the bottom of the fuel tank.
Did some reading and found out that a CAT runs at about 800 degrees F. I assume this temp is reached by keeping the exhaust moving around in the Cat and increasing back pressure. Any way the temp of the Cat is not the critical factor here, but the location.
I could not get the thought out of my head that I had in effect a HOT PLATE under my gas tank. I am thinking that if the heat from the Cat is warming the gas inside, and as the gas gets warmer it expands. That as the gas heats, expands the computer controlled injectors add more fuel to the engine to make up for the lost density of the gas. So to validate this "theory" I bought a probe thermometer. It has the sensor at the end and approx. 24 inches of steel cable that allowed me to put the sensor directly into the fuel tank. My results from 2 tests were:
Test one, 50 mile run with 2 shot stops and a 30min stop for lunch. Be fore engine start up after a rather cool S. FL. night (65 degrees) Ambient temp of air 76 degrees F. Temp of fuel 74 degrees. Placing probe in gas and Velcro the read out near the glove box, the wife and I headed out.
Warm up approx. 5 min., Fuel temp no change, 2 Miles to gas station, shut off, went in for bottled water, smokes, and a candy bar for the wife.
Approx. 10 min before restart. Fuel temp 80 degrees. The fuel had warmed up as it was sitting after approx. 10 min. of engine run time.
Left Homestead Fl for a 22 mile run to Key Largo, ambient air temp at this time was 78. Fuel 80. Got on US 1 and was running approx. 55-65 miles an hour. After just a few min, the fuel was heating up. Approx 2 degrees in 3 min. Approx 30 min. latter when we stopped for lunch at Key Largo the fuel temp was 116 degrees....THE TEMP of the fuel was going up as the bike was moving!

What I learned was the CAT does in fact act as a hot plate under the fuel tank. That the fuel will heat up when the bike sits after running. That the fuel temp goes up as the bike is moving at normal highway speeds. Total time for the this test was a tad over 2 hours, the total running time of the bike was 1 hour 10 min.
The second test was much shorter. Cold bike ambient air temp 81 degrees, fuel temp 74 degrees. Again bike was sitting all night and night low tem was 68 degrees. Start bike, warm up approx. 5 min. 2 mile city traffic to our favourite breakfast place. Total run time less then 20 min. speed not over 25 mph. Fuel temp on shutting down 99 degrees. 45 min. for breakfast. fuel tem 85 degrees. Run time home less then 15 min. Fuel temp 107 degrees. Shut down bike and 30 min. latter fuel temp was 98 degrees.
What I learned here was the fuel temp goes up rather fast, and down rather slow.
I have not down a test a full one highway speeds of 65-75 mph for any extended time. Truth be told, I do not know if I want to know fuel temp after 3-4 hours of riding......
2 Questions I need some input on: 1) I know gas does expand when it gets hot, are the temps I recorded high enough to cause expansion to the point it could affect gas mileage? 2) I know that the back pressure from the Cat may effect gas mileage, but to what degree I have not a clue.
My plan now is to get a Cat bypass pipe. I am looking at near $300 to purchase and I would assume another $100 or so to install. Is there anyone who has put a Cat bypass pipe on their 996 Rotax and saw an improvement in gas mileage?
Rather long post, but wanted you to have the background on what I did etc.
Thanks a bunch,
Doom
:doorag: