Thread: Major loss in RPMs?
07-27-2010, 07:50 AM #1
Major loss in RPMs?
I have a modified 260X. My RPMs went from 8,420 when the temp is near 60F to 7,820 yesterday when the temp was 98F. I would expect a drop of about 300RPMs, but I think 600RPMs is too much? I know my ski is a freak of nature and should not be running 8,400+ with a stock prop... so please let's not even address that subject in the thread... OK?
My questions are: Why such a drop? What experiences have you had in this area and what did you to determine the cause? What did you do if anything to correct the problem? What RPMs do you run in the heat?
07-27-2010, 07:51 AM #2
its heat soak phil. the heat and humidity kill the motor.....
have you done the intercooler feed mod?
07-27-2010, 08:08 AM #3
07-27-2010, 08:14 AM #4
- Join Date
- Mar 2008
+1 phill the ambient temp has everything to do with what your saying. Cooler air is thicker than hotter air. My ski will run differently at one lake than another. This one lake i go to is spring fed and the water temp and air temp is cooler closer to the water surface thus the ski runs alot better. If i am riding on the Tn river the ski doesn't want to run as well cause the water is warmer and the ambient ai temp is warmer . more humid
07-27-2010, 08:17 AM #5
07-27-2010, 08:23 AM #6
Phil, I have also seen a change in rpm's when it gets hot, usual 300 to 500 rpm's lost.
It sucks, but thats how these Utra motors do in the heat.
07-27-2010, 09:14 AM #7
wow, so if it was winter right now I would be turning close to 8800rpm on a stock charger stock 260 prop. I guess 8250+ in Fl humidity isnt bad.
I thought 300rpm was closer to normal but it is good to hear of 500rpm difference
07-27-2010, 09:46 AM #8
07-27-2010, 09:52 AM #9
from what I have read in past threads, I think this issue is primarily the results of Heat, Humidity and A/F ratio. What do you guys think? Phil have you checked you A/F now that its warmer? Mine had to be changed, and will be changed again. Any input?
07-27-2010, 10:00 AM #10
Subtlesoldier you say you are getting 8,250 in high humidity and temp. That is incredible! Are you saying that you have rached 8,800 in the winter on a 260X? I am running 16lb. of boost on my best day and I can only run 8,420 on my best day.
JmaTak9 is right, I have to get an A/F guage and check out my ratio before I can judge anything.
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