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aka: mOtOrHeAd MiKe
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Discussion Starter · #1 ·
This is stemming from last night's trip to the track (with the added boost) and performance dropped off from the last trip. Both ET and MPH were down. The best I could muster was 13.8 @ 102mph vs. 13.59 @ 103.4mph 2 weeks ago.

The difference IMO, was the threat of rain. It did indeed start to precipitate as I was coming up the return road from my last pass.

What sort of power/performance loss can be expected from 90-100% relative humidity?

I understand that the air density drops off as water molecules are replacing oxygen in the mix. But, could it be worth 2mph? Probably more due to the extra 3psi of boost over the last trip.

Oh, and I also found out that even with 2 fuel pumps and propane, my car likes more fuel up top. But, is too rich down low (1st & 2nd gear). Go figure.
 

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I'm the Best!
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14,835 Posts
my car is alot slower with the humidity also.
 

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Premium Member
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43,745 Posts
humidity has less effect than air temp, but, still, with humidities in the high percentages, it does have an effect on air density.

If you do a search, you will find an equation for the calculation and you can see that very high numbers can really hurt...it is worse on warmer days by a long shot.



 

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2 GN's = No money!!
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5,125 Posts
Mike,

I have my drag log book out and a couple of years ago I was racing at night at St.Thomas and I have a really cheap "weather station." In the course of the evening the temps dropped from 75 F to 69 F but the humidity went from 69% to 86%. The track was only running 1/8th mile that night but my ET slowed from 7.53 to 7.66 so you can see how it effected my car. My mph was off that night but it dropped from 90.76 to 89.77 :mad:

On the way home that night my dad was asking me what was wrong with the car but when I showed him the humidity #'s he realized it was just the weather. We used to bracket race EVERY weekend the track was open so I learned to bring a weather station, it is very helpful for dialing the car in.
 
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