I'm looking to really understand DA and how it affects our cars at the drag strip. I have a basic elementary knowledge on what DA is and how it works and I have looked at the general formula's many use to calculate DA as well as the various websites that do that for you, (Dragtimes, Airdensity, etc) In a nutshell, lower DA = good, higher DA = bad.
So, that brings me to really my main question. How does it REALLY affect our cars, being that they are FI? Let me give you a better idea of what I'm after. The past few weeks at my local track here in Tampa/Brandenton (Bradenton Motorsports), the DA has been anywhere from 900 to 1700 (last night). My car has been trapping consistently 5mph (130 vs 135) slower during those conditions. However, on the dyno the car is making solid power for a FBO+e85 car. Now, with my basic understanding of DA, at sea level, the car should be making full power and trapping what it would normally trap as 900 DA isn't too bad. Additionally, the car ran a 10.5 only trapping 130mph with a 1.61 60ft.
Last night, the DA was 1700. With a set of fresh tunes to test, my first time out was 10.4@130 with a 1.64 60ft. Each run thereafter was also 130mph up to the 4 runs I got in. So what I'm thinking, and please feel free to chime in, is that I can't just look at DA. Because when you break down DA around here, you have to look at air temp AND humidity. The past 3 weeks the temps have been around 73-80 degrees out at night. But, the humidity has been 75-100%! So now I'm "assuming" that my problem with missing MPH is the humidity. Does that seem to be an accurate assumption? We're still fine tuning the car but I feel as if the car is running strong and its consistently hitting the same numbers run after run. Other FI car owners that I talked to last night said they were having the same issue with their cars trapping 5-7mphs less but still pulling in really good ET's. That's the part I really don't understand. Does that mean the car is making good power down-low to mid then falling on its face at top end because of the humidity? This is on a FBO+e85 stock turbo setup.
Does humidity rob our cars of MPH and if so at which percentage (50%+?, 70%+, etc..)? Can you still have a good ET even though you're trapping lower than usual?