weather difference and 1/4 times

B

blackdieselram

New member
i went to the track a few weeks ago and ran a 12.7, the weather was in the mid to high 70s and the humidity was pretty low. last week i got some 305/50/20 tires to replace the 315/70/17 i had when i made the last run thinking it would help my times with lighter weight and a smaller diameter tire. tonight i went to the track and the best i could run was a 12.9, it was in the low 70s and the humidty was very high almost 90%. im just wondering if the weather can make that much difference or if there is something else that slowed me down.
any info or thoughts would be really appreciated

thanks
 
from what i can remember the wind was very simillar. i checked the difference on the hp calculator and it is only like 20hp but i figured the smaller tires would have made up for it:confused:
 
The 305-50s probably changed final drive ratio enough to wind up the engine further away from peak HP through the traps... smaller diameter tires work better when you've got the extra RPM in the powerband.

What happened to the 60's?
 
60s were down also too. went from 1.7x to 1.8x
my 1/8 was slower also.
it did seem like the engine was reving higher before it shifted for some reason. is there anything i can do to make it shift sooner?
 
Did you update the Smarty with the smaller tire diameter?

Also, you'll get more out of the 305-50s with TNT-R (don't know which version you have).
 
yeah i had tried it with the actual size, then i also tried it with larger and smaller size to see if it made any difference but it didnt.
im running the tnt, i dont have enough work done yet for tnt-r.
i also have the dtt shift enhanser and tried the different settings on that and aslo with it disconnected but it still tries to wind up almost to 3500rpm before shifting.
 
What's the elevation of your track? DA (density Altitude) will effect your times, water grains in the air will make the DA higher, or seem like you are racing at a higher elevation. Check out this link it will explain it better.

Density Altitude (DA) Calculator - DragTimes.com Drag Racing, Fast Cars, Muscle Cars Blog

Here is a link to the calucator if you feel so inclined. You want low DA, meaning sea level with low temperatures, low humidity and high barometric pressure.

DA Calculator - Density Altitude Calculator - DragTimes.com
 
If your 60' were off by a tenth then that's prolly where the difference was...ur 60' is where you make or break your et. Were your trap speeds close to the same? If they were then the 60' was ur problem. Did you leave at ther same boost both nights?
 
If your 60' were off by a tenth then that's prolly where the difference was...ur 60' is where you make or break your et. Were your trap speeds close to the same? If they were then the 60' was ur problem. Did you leave at ther same boost both nights?
 
my 1/4 was 1mph slower and my 1/8 time was slower also. my whole time from start to finish was slower.
i was leaving the line with the same or maybe even a little more boost because my new tires can hookup better. i was leaving at about 20psi, my old tires would just spin if i did that with them.
here are my time slips
127.jpg
time2.jpg
 
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Yeah, looks like the bad air hurt your overall horsepower. MPH is an excellent indicator of average horsepower during the run. 1 MPH is significant enough in my opinion to call it weather related.

Air temperature has a huge impact on density altitude. I went to NHRA last weekend and the D/A was announced as 4200'. The air was really dry here in Las Vegas but it about 85*F and barometric pressure was a little low. For reference, the elevation at Las Vegas Motor Speedway is 2028' so with really dry desert air the D/A should sit around 2000-2500' depending on air temp.
 
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