08-18-2010, 08:45 AM #1
Prop pitching an rxp in Kansas approx 1400' above sea level. Need help.
I recently sold my RXP to a buyer in Kansas. It has a riva ecu, et140R charger, 4" intake, etc, etc, and a 15/20 solas.
I live in CT where the temp is high 70s most of the time, the humidity is low, and we are right at sea level. I had the prop pitched to a true 15/22.
The buyer lives in Kansas where the conditions are different- particularly the fact that he has approx 1380' of altitude.
I presumed that he would be off by around 200rpm or so but he is off by about 500 rpm. He/I/we need help repitching his prop to get him in the ballpark. Can anyone offer any input/insight? I have ZERO experience tuning a ski with altitude and I hate playing the guessing game.
I put him in touch with Woody because he has experience tuning with altitude but I figured I would also put it out on GH.
LMK what you think.
08-18-2010, 09:06 AM #2
Nozzle size ??? I bet 250 is from altitude and 250 is from the August heat. If he has adjustable rings then just take all out and confirm there is an RPM change.
08-18-2010, 09:08 AM #3
You can repitch,but 500 rpm is to far off,you would need 5 mm that's to much to repitch.
Repitcing works best for +- 200 rpm.
He can take the airfilter off the kanaflex ,this will give around 100 rpm also.
08-18-2010, 09:10 AM #4
He should get his A/F in line first considering that he's probably a bit rich and costing some rpm's and then he should sell the re-pitched 15/20 and buy a new 15/20 and d-pitch from there. Pitching these props back and forthe makes them weak and more likely to break. Otherwise if he wants to take the chance and use the prop he has he could send the prop to someone and have it pitched to around a 14/19 and go from there.
08-18-2010, 09:12 AM #5
08-18-2010, 09:30 AM #6
Afr is also important as mentioned earlier,but bending the prop back will help a lot.
Between winter and summer i loose 250 rpm's easy,afr also varies.
If you want to be safe ,set your afr's at start of the season,this way you will be a little rich during summer,but you won't blow up your engine in the colder months.
This is for recreational use,if you want to fine tune,you just need to do some more adjustmenst now and then, to have good afr numbers,and reach your top rpm's.
08-18-2010, 10:22 AM #7
The ski is running open kanaflex.
He adjusted AFR first. I explained to him how to do it and he borrowed an LM1 from a friend. I adjusted it so it was a bit rich before I sent it off just to be safe. He says hes got the AFR locked in now around 11.7ish@wot
I dont know what his temps are.. I did not take that much into consideration. We are high 70s to low 80s most days with fairly low humidity. I didnt expect Kansas to be much different from here although Ive never been there. I dont think hes getting temps of 98 degrees with lots of humidity.. but I could be entirely wrong.
I didnt expect the pitch to affect his rpms by more than 200 or so. When he told me he was getting between 7900-8000rpms I was surprised... I want to help him but im obviously not there to see it and I dont have any experience tuning a ski in altitude. I was hoping we could get a number that would get him in the ballpark.
I also encouraged him to contact Woody- or Erik@ Speedfreeks or Duke, etc.
08-18-2010, 10:26 AM #8
He said he was very happy with how it was running now but I cant see the ski running at all well with 500rpm missing.
08-18-2010, 10:28 AM #9
08-18-2010, 11:04 AM #10
He is probably riding at 5,000 ft + Rad.
He has a challenge getting the right pitch to increase rpm and not kill the holeshot and top end. Been there done that.
Nozzle size will not influence rpm change drastically with high Rad.
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