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HOW TO TUNE FOR WEATHER CHANGES

Here in Arizona we have the good fortune to have 3 wonderful months we call winter and then of course there is HE** ,I mean, SUMMER. Racing here in the winter is, of course, one of the best parts of living here as our vehicles always seem to run the best with good barometric pressure, cool temps and low humidity. But then we see what happens when the monsoon season is upon us! It's hot, it's humid and it's just plain nuts trying to get the car to run the number.

No need to check the toolbox for left over parts, just start with these two things: timing and jetting. We know when the monsoon starts because our swamp coolers stop working and we don't cool off as well as we did. Why? It's has to do with humidity but in a different sense. It's called the "dew point" and it is the true indicator of the amount of moisture in the air. The closer the dew point to the current temperature the higher the relative humidity.

That's why they consider the start of the monsoon to be 3 consecutive days with a dew point average over 52 degrees. When we get more moisture in the air it allows us to run more timing for the same reason fighters and other aircraft used water injection. More water in the air means there is less of a chance of the engine detonating. If you are running a sophisticated set up such as a weather station with "CREW CHIEF" software you should be able to use the old rule of 1 degree of timing for every 10% increase in humidity up to a max of 4 degrees. Just be sure you keep an eye on your plugs and look for the signs of detonation! If you don't have access to this type of equipment and I know a lot of you don't, use the old stand by of: if performance drops off, you've gone too far. Just back it up to the last improved setting.

Changing jets can also show some rewards. As it gets hotter, the air becomes less dense, which in turn will decrease the amount of fuel that can be used by the engine. The standard rule of thumb is to decrease the jet size by 1 for every 20 degrees F increase. You can also adjust the jets by 1 for every 800-1000 feet of density altitude but as always let the spark plugs and the performance increase/decrease be your final guide. Hopefully you can use some of this to help your engine run cleaner and more consistent during our good ole summer monsoons!

By the way, CREW CHIEF software is available on the website, along with the best weather stations and data acquisition systems on the market by clicking on the banner for RLB ENTERPRISES.

by Robert Plowman