Before we went, I did a lot of hard thinking to try to remember how to use my E6-B flight calculator to determine the density altitude of the air in Meiringen at the average race day temperature. Then I found out I'd need to know the pressure altitude to do that, which I couldn't find without actually being in Meiringen and having an pressure altimeter. I don't have a Cessna handy, so I wrote this off.
I thought about it some more and realized that I didn't really want to know the density altitude or pressure in inches of mercury anyway; I just needed to know where to find on a 85 degree Sierra summer day the equivalent atmospheric pressure to 62 degrees F at 2,000 feet in elevation. I looked around at some density altitude charts until I found this guy, which conveniently had the Pressure Altitude on the Y-axis:
The upshot is that we tested at 800 feet ASL and 6,000 feet ASL instead of at 2,000 feet ASL and 8,000 feet ASL because it was 85 degrees today.
We tuned with this thing:
We started at 800 feet with the filter closed and had to downjet, which was reassuring. Next, it was a 70 mile drive up to 6,000 feet. (California Interstates are much different from Swiss mountain passes. I'll be climbing that altitude in about 30km during the race.) At 6,000, we opened the filter, found that it was still too rich, removed it, and found that it was less rich. It'll have enough power, but less so.
Spoiler alert:
We used a GPS to test my climbing speed. I reached a top speed up an 8% grade of 16 mph from a standing start. I reached a top speed coasting down that same grade after about two hundred yards of about 27 mph. The winner, you remember, will be the one who completes the course in as close to 4:34 as possible, the time it takes to complete the course at 18mph. I think I will have time to rejet if necessary. Remember, on the flats I go about 18.5 mph with my stock cylinder and stock Bing. 11x52 gears for the win.
PS: Have you seen the new Motomatic Mopeds online store?
What kind of RMP is that turning when you hit 27mph? I hope your bearings and crank can handle it! Are you going to keep track of the times on your runaway descents so you can calculate how much time you have for jet changes? Perhaps you should keep the spare jets mounted on new emulsion tubes, then the correct size nut driver makes the change super fast, you can just tilt the carb on the intake and swap with it still mounted to the bike.
ReplyDeleteI'm going to use a list of checkpoints and a wristwatch.
ReplyDelete