Dyno Guru's, I have a question?
 

The dyno I tune on always seems to read 10rw or so lower than the dyno I used to use. I think it might be weather correction related. Today I tuned my buddy's mild 402. I got 516/483rw out of it which was about 35/35rw more than when he drove in but I think it should do a little more.

Here is the question. What should the correction factor be with numbers like these. Temp 88.01 F, Humidity 51%, Baro 30.16. It gave me a correction factor of 1.00. I just think the correction factor should be higher.

I wish it was 88 degrees here.


But with those conditions = 1.002

Thanks. So I guess it is correct then. I thought SAE was 70*, 30% humidity or some thing like that?

Your barometer is higher than the SAE 29.92. This is going to bring your correction factor down. If you had been dynoing with a 29.92 barometer and the temp and humidity you have, your correction factor would have been 1.012 instead.

Brett...for shits I looked on drag times dot com and for instance Fayettnam on the 15th of Aug 2009...pretty much the whole day barometer was 30.10-30.20 so I guess it was reading correct...I remember last time we dynoed mine the humidity was like 10% off of what the local weather station you called was seeing.

Dynojets weather stations humidity are typically off a good bit. Don't know why, just that all the ones I've ever tuned on, including my own, and the one here at Va Speed, have ALL been off by a fair amount. I've seen it rainin outside, and read less than 50%.

Best thing you can do is blow a fan on it. Move ambient air across it.

Thanks for the responses. I just use the thing for tuning really. It says what it says then we take the car to the track or street and see what it is really worth. I was just trying to gain some knowlege really. I just figured this motor would go 520 with out much trouble. We had a 518 pull but there was a bad tq spike so the graph was crap. The heads are pretty crappy for the combo so it makes sense.

Being in the field I am in, I have always had a 'pet-peeve' about some of the dyno weather station setups. Not so much the quality, but as with any instrumentation the calibration (or lack of) can deteriorate over time.

Most barometers need at least two adjustments per year. The 'humidity' deteriorate as dust, oil, or any contaminate collect on the sensor. And conditions are only representative of the location. Senor(s) inside or out, etc.

Whether it is a minor issue or if it really skew the results, I always suggest a basic cross reference either by referencing a nearby weather station (though that can vary) or if you are really hardcore, a cheap hand-held weather station.

True a lot of 'games' can be played to manipulate any data, including dyno correction factors. But, for the most part a 10 Hp difference from one dyno to another is well within an acceptable range. Like everything else it is just one tool to use.

..WeathermanShawn..