Would you expect a change in et if the barometer stayed at 29.77 but the da ranged from 900 to 2000ft during the day? The air temp went from 68 to 76f and water grains 64 to 83 as the day went on.

Too many variables to answer... depends on cubic inch, compression ratio, fuel, forced induction / naturally aspirated, etc.

472 Pontiac, 10.8-1, 85cc d port aluminium heads, 93 fuel, 850 carb, cowl hood.

I don't think .05-.06 would be unusual. That's just based on DA, although it's been a real long time since I've run gas.

With my door car on alky, I'd be thinking about .04 just based on the water grains.

yes , Tony is about right . Thats what mine does with that sort of da swing .


Tex

The DA math doesn't add up.

One degree in temp equals around 100 feet of DA for a quick reference ( depending on humidity and baro changes ). 8 degrees of temp change is about 800 feet, and you show 1100 foot change.

What did the humidity change during that time?

1100 foot swing of DA on a pump gas engine is about .055 to .085 in ET with normal jetting.

.05 - .06 on my low 10,s Pontiac

That would be about .03-.05 for my ride...without the barometer moving.

quote:

Originally posted by Ken MacNicol:
.05 - .06 on my low 10,s Pontiac

Length of the reacetrack would be another variable.

Not to derail this thread, But. The OP does not list what is being used to measure weather. I’m looking to replace my 199x PerformAIRE with a new handheld model. What are those with “handheld” weather stations using and opinion on the ET predictor included?

quote:

Originally posted by markemark:
Not to derail this thread, But. The OP does not list what is being used to measure weather. I’m looking to replace my 199x PerformAIRE with a new handheld model. What are those with “handheld” weather stations using and opinion on the ET predictor included?

John Bates has a cool phone app that is really good.

EZPredictor2

quote:

Originally posted by markemark:
Not to derail this thread, But. The OP does not list what is being used to measure weather. I’m looking to replace my 199x PerformAIRE with a new handheld model. What are those with “handheld” weather stations using and opinion on the ET predictor included?

Computech RaceAir Pro. I had good luck with that before moving to the RaceAir Cloud.

As for phone apps I've yet to see one that uses local weather.

quote:

Originally posted by SP 124X:

quote:

Originally posted by markemark:
Not to derail this thread, But. The OP does not list what is being used to measure weather. I’m looking to replace my 199x PerformAIRE with a new handheld model. What are those with “handheld” weather stations using and opinion on the ET predictor included?

Computech RaceAir Pro. I had good luck with that before moving to the RaceAir Cloud.

As for phone apps I've yet to see one that uses local weather.

John's app retrieves the nearest weather station data, OR, you can input your own gauge data.

BARO, TEMP, HUMIDITY %

Select Gas or Alky

quote:

Originally posted by markemark:
Not to derail this thread, But. The OP does not list what is being used to measure weather. I’m looking to replace my 199x PerformAIRE with a new handheld model. What are those with “handheld” weather stations using and opinion on the ET predictor included?

Gone from a performaire eclipse to a computech race air pro, using one run preductuons, is a lot closer to the mark with methanol for me, i dont take it as an absolute.
I still check it with notepad and biro but it is close.
Cheers

I had an Altronics weather station, but its no longer offered, obsolete. Weather was swinging wildly with it. Buddy got the Computech RaceAir Cloud, and when mine was all over the map, his was pretty stable. So I got one of the same. Last event I ran here was the first time I used it....was testing so didn't use it's prediction, but readings were very stable. Yes, conditions did change during the day, but it didn't make 1000ft swings every hour like my Altronics did.... I use CrewChief Pro for my predictions. It was all over the map too with the Altronics weather station, not a fault of the program though. Was VERY accurate with the computech, as I entered my runs from testing to see what it would show....