altitude

[lankydoug]

I see a lot of questions asked about altitude and jetting changes here on the forum. Here is something to consider. The actual altitude you are at may not even be close to the air density altitude. I drove a drag race car professionally around the mid west for years and checked the air density altitude before every pass when possible. You would be surprised to know that at a 600ft above sea level local track the best air I ever raced in was 1500ft and many times in the hot humid summer it was 3000-3500ft air. When tuning an engine this is the number that counts the most. So when you are going to a higher altitude but a cool dry climate you may be surprised how good the air is just as the air can be as poor as 3500ft at an actual altitude of 600ft. My advise would be to get a small weather station computer, Casio made a good one a few years ago, and keep a log book. You can compute it yourself with a barometer a thermometer and a humidity gauge as well. Once you have a baseline set for your engine you change jetting using data from your notebook and get it exactly right the first time. Besides air density altitude the other main factors to consider are ignition timing and the fuel you are using so only make one change at a time and be consistent when gathering your data.

[roostafish]

Excellent post. The weather computer would make it a piece of cake.

[lankydoug]

Originally Posted by roostafish

Excellent post. The weather computer would make it a piece of cake.

Thanks roostafish,

The computers that came out about the time I was getting out of racing had a notebook integrated in the software package so if you went somewhere different or the weather changed you could check the air density and it would pull up all your notes that you entered at that similar altitude including personal notes on track conditions.

Lets face it, most of the time a guy is faster because he/she is a better rider. It's when riding skill is equal that the guy with the better set up will win. If you run on the lean ragged edge and the air gets better in the evening as the sun is going down you are likely to slow down and possibly hurt your engine. I have seen the air change over 1000ft in less than an hour. I recommend going a hair on the rich side and stay away from fuel with any kind of alcohol not just because it's corrosive but it is affected way more by changes in humidity. Usable power is the key after all we aren't racing dynamometers it's what can you put to the ground.
Doug