My buddy has a modded 2005 500 carbo (cam and carb work), while I cam up with my trusty fuel-injected 700 XP ( slightly modded with PowerCommander, 700SP cam, 700SP ECU, throttle mod, red spring).
Both Rangers started easily at 7k feet. The XP like a champ, the 500 carb less so, but adequate. The 500 carbo had plenty of thin-air grunt off the line, but the XP would quickly match and surpass it, with a modest amount of speed betterment as the RPMs climbed.
Here's a cool Density-Altitude calculator to tell you what your elevation and temperature feels like to your Ranger. http://wahiduddin.net/calc/calc_da.htm For "Altimeter Setting" just type in 29.92 -- it should be close enough. For dewpoint, consult http://www.weather.com for your zipcode.
For example, 111 degrees F at 1,100 feet (Phoenix, yesterday), equals 4,658 feet.
Flagstaff at 7,000 feet and 85 F equals... about 10,400 feet.
What did the pressure altitude do to my Ranger's performance? Well, it still had enough juice to hit the rev-limiter -- it just took it a few tenths of a mile longer to do so. Performance from an acceleration standpoint felt like the XP when it was stock, and just broken in.
Also, I had heard some here say that when going to altitude/temp extremes that one shoud turn on the ignition switch but not start it for several seconds on the theory that the ECU is recalibrating. I'd always thought this was bunk, but during the weekend, I kept forgetting to "recalibrate." Finally, on one run (it just so happened that my buddy challenged me to a race) I did the re-cal, allowing 15 seconds before cranking. Seat-of-the-pants seemed to say that it worked... but there's nothing like a race to get your adrenaline up and your judgement down. :) I can't say for sure.
On Sunday I got to test out my new re-jetting (old was 150 Main, DEK-3, and 38 Pilot; new is 148, CEK-3 and 35 Pilot). Down in Phoenix, the new jetting certainly changed the sound of the motor. It went from Bwaaaag to ring-ting-ting-ting. I had misplaced my plug wrench so I didn't get a chance to see how it was burning.
The riding around Munds Park to Mormon Lake ranges in the 7,000 foot range as well. The KDX ran as usual -- still had the 1/16th throttle burble. But I did hear a little high RPM "voop-voop-voop" as if the motor was missing or too lean or too rich. But that was only when it was warming up. Hmmmm.
So now we have some extra data points. Lean runs fine down low in Phoenix, but at altitude (where it is running relatively richer), and during warm-up, I had some voops. Could it be the voops were caused by the combustion chamber not being able to burn the fuel at that RPM? ie, too rich? The voops when cold definately have me wondering.
Anyway, the trails at Munds Park were mostly volcanic and rocky. But we did find some spots that allowed us to stretch out a bit. Problem is, we found them when it was nearing time to head back home.
Here we are up on Mt. Elden's hang gliding launch (9200 feet). We were re-living our old cross country hang gliding days.
And here is Jolie, begging for a ride on the KDX 220R. Vince's 500 carb in the background
Oh, and for you Sadists, here I am nearly falling out of the truck bed after my very first time riding the KDX up the ramp. I was foiled by an old car mat that I have in the back of the bed. My front wheel rolled up on it and it slid to the left. Luckliy, the KDX pinned my right leg to the bed wall or I would have fallen off the side. My Moose riding pants protected me from the toasty-warm PC pipe. Not the horrified look on my daughter's face.
Rick
