A RAD (Relative Air Density) gauge is a one way to go. It won’t show humidity, but the affect of that varies wildly. RAD will get you in ballpark and give you a good reference point.
I have something like this…
You can get personal weather stations pretty inexpensively these days. Although I can’t speak to accuracy, I’ve heard some motorcycle racers claim good results with them.
This one I think most of us would call the “gold standard” as it does some of the calculations for you. I’ve had one of these as well.
All of these methods require you to have a baseline to go from for your motor package… nowadays these baselines are common across the same engine modes and brands in spec series. In the past that was not the case… you’d really need to baseline your own equipment.
Hypothetical baseline example… Say you find the best jet for your kart on the day was a 100 (0.1”) and the RAD was 100% that day.
Next day you arrive at the track and the RAD drops to 96%, well now you need to drop your jet AREA by 4% to have the same jetting. Area emphasized because many (not all) jets are sized by diameter.
At the end of the season in morning practice you see the RAD at 105%, you better jet up or kaboom (at least with the high performance two strokes)
These are the kinds of calculations that the race air pro can do for you. You enter your baseline jet and ADR (Air density Ratio), it takes an air sample and spits out a suggested jet size based on the information you gave it.
This is a little harder with screw based pumper carbs of course, but knowing the air density can be a valuable tool to guide decisions… Weather it’s from a race air pro, a local weather station via your phone or your trusty analog RAD gauge.
All that said, there’s probably neater tools available now with more connectivity and options.
Tell me, what number are you getting For barometric pressure? Do you have any idea of your altitude? I could be wrong, but I don’t think so. My phone only tells me temperature, but I’ll guarantee you it’s not the temperature where I at.
Alvin, I don’t know what phone you have, but most have everything required except yes, your exact local temperature. Not that the temperature in the pits is accurate anyhow on a hot day. But this can be easily overcome with a simple external probe, such as this Bluetooth device: Temperature and Humidity Probe
a) The baro sensor built into my phone; and
b) The nearest weather station pressure (which is reported as corrected to sea level) corrected manually for the altitude of the track (determined using google earth & gps)
This, along with local temperature and RH (or Dew Point) I can calculate Charge Density, either as kg/m3 or DA.
I do not know. I do not do anything with it. I do know that when Dark Sky (weather) app was still available on my phone they requested I share my barometric pressure as part of their hyper local weather forecast. That way they could monitor weather change from everyone that was sharing data.
I am sure the phone has a temperature sensor also, but I agree it has nothing to do with what the phone is reporting since the phone is, in a random way affecting its local temperature so it can not be relied on. To the best of my knowledge it has no humidity monitor other than possibly an internal sticker or paint to detect water ingress for water damage issues
Below is a link to a website that’s free and has most of the tracks in the US or close to one you can use with all the up to date weather information. Everything from Air Density, Density Altitude, Corrected barometer, Uncorrected Barometer, Dew Point, etc… At the top of this page is a link that says US Tracks. Their all listed state by state. This site is awesome.
Thanks Denny for the link. This would have been great if we were still running long tracks with a fixed jet carb. Maybe I’ve missed something, but I don’t see any sites that are close to a kart sprint track.
I do have a battery operated barometer. I get the barometer reading from the closest weather to my house. I know my altitude and can calculate the correction factor to get me to the uncorrected pressure. The gauge gets set once for the entire year.
With needle jet carbs, the barometer is used as a tuning aid for gear selection.
Air density is arrived at using two “measurements”, barometric pressure and temperature. You’d be surprised at how much those 2 numbers can change during a day and over a years time span. Here in Austin Texas (nearby) I’ve seen the air density go from the high 80s to just over 100. There’s no way you can just leave your carb set to one setting over that range of air density readings and be competitive all the time. Besides that, during the correction math on that reading from the airport is poor substitute for the air density gauge!
[quote=“JR_Garcia, post:113, topic:5916, full:true”] I´d love to use but I never found an app for my engine IAME SUDAM Do you know if any app is suitable for this engine? [/quote]
I’ve never seen a app either. Longacre has some instructions for the use of their air density gauge online. Basically it says to compare jet settings to performance. On that day when you’re running your best, write down your jet settings and the air density, use that as your base and adjust accordingly. You a 1% change in air density calls for a 1% change in fuel delivery. I have Excel spreadsheets for calculating changes in jet sizes. Email; [email protected] for your free copy.Good morning thank you
