Drag Racing Tech - ET/MPH vs. Temp./Humidity
09-11-2011, 03:01 PM
How much does everyone's car's ET and MPH vary with temperature and humidity? Last night I was racing in my local series going 11.35-40 at 120. As the night went on the temp dropped and humidity went up eventually past the dew point. My car kept getting slower ending the night with two 11.70's at 116. No other cars including another LT1 and several LS's didn't seem to be affected and some even improved. Is there something I should be looking at, mine actually seems to run better when it's hot out! WTF:confused:
09-11-2011, 03:10 PM
Hmmm I wonder if your clutch started to go?
09-11-2011, 03:29 PM
I thought that too but I would think my 60' times would show it, they stayed between 1.58 and 1.62 all day. They stopped racing twice due to rain and having to drag the track so I thought the 60' would drop off more than it did.
09-11-2011, 03:42 PM
My clutch seems to grab almost too hard on the line but im starting to think it might be slipping since Im shifting into 5th NA on 28s. Weird part is I cant feel it or see it on the tach.
Maybe your motor was just getting heat soaked? How long was the cool down between runs?
09-11-2011, 04:21 PM
Not much cool down but it never got to 160. I wonder if it's slipping in the upper gears, I did notice the shift light coming on as I crossed the stripe on the last pass and it doesn't usually do that. Is it possible for the clutch to grab hard enough to lift the front end in 1st but then slip in 3rd and 4th?
FYI I'm on 28's as well and usually just above 6K at the 1320 in forth, 4.56 gears.
09-11-2011, 04:37 PM
Clutches usually start to slip in the higher gears first, but with those 60s you would think it would be noticable off the line as well. Looks like we both might be in the same boat if we cant figure it out. If I do pull the trans the T56 is not going back in.
09-11-2011, 09:14 PM
09-11-2011, 09:23 PM
Typing in my numbers using the calculator still shows it being 4 tenths and almost 5 MPH difference even considering the weather. Just got back from a drive and the clutch is holding strong in 4th and 6th driving as slow as possible and going WOT.
09-12-2011, 09:01 AM
Data log NE of the runs??
09-12-2011, 05:06 PM
I wish I could have that would have made this alot easier to diagnose! It's running on the stock OBD2 PCM and I don't have tuning software.
09-12-2011, 05:45 PM
I've seen about 2.5mph and 2 tenths difference between 75* ambient (slower times) in September to 50* ambient in November. To go the other way in more humidity/heat doesn't really make sense...
09-13-2011, 12:59 PM
My Nova goes from 11.teens @ 119 mph in killer sea level or lower air to 11.40-50s @ 114-115 mph in summer air (at or above 3000 DA, this summer was over 90 degrees most times and humidity anywhere from 20-80 percent).
As mentioned, keeping track of weather and track conditions will help you make a more accurate call to diagnose your issue. The temp dropping and humidity coming up can make some cars faster, while others stay consistent. I've been racing 20 years and you see all kinds of results.
09-13-2011, 02:16 PM
I've varried 2 tenths in the same night before, The weather gets a little funky here where it will be 80* during the day but at night in the low 50s. Thats a Huge change and can definetly throw things off.
I would consider having someone copy your tune and convert to OBDI so you can use datamaster or datalog of some type.