I've been trying to find out if or why I've been losing mph on the second half of the track. After reviewing some of my previous timeslips, I found that typically I was picking up between 23-24 mps in the second half . Normally when I ran 88-89 in the 1/8 th, I would run 112-113 in the quarter. About a month back, I found that my mph had fallen off quite a bit. A short time after that, my transmission failed. I figured that maybe the tranny had been slipping in high gear causing me to lose mph. I recently had a new tranny installed but I'm still having the same problem. I ran a best of 12.09 yesterday but only at 109.4. Before these problems, I was running between 112.5 and 113.7 in this type weather. I did notice that my valvetrain was getting very loud in the upper rpm range so I'm now wondering if I might have weak valvesprings. What do you guys think? I cant understand what hold the car back so much. I thought it might have beena lean condition but my o2s were reading .890 mv. What do you guys think?

 

I only pick up 21 mph in the last 1/4 mile but I'm also topped right out at the finish line.

Even top fuel dragsters running 330 mph only gain another 60-70 mph in the last 1/4 mile.

 

I gain about 30mph

 

I gain 27mph.

 

Back in the fall of '99 I was gaining 27mph (81-108), but now I am only gaining 23 (88-111). I think my clutch is slipping so I will have a street twin going in next spring along with a new fuel pump.

 

26mph 86.5-112.5

 

i pick up ~24~ mph with my LT1. my big block pontiac picks up ~22~ mph. both cars are NA...the LT1 is a 6 speed, poncho is an auto.

 

I gain 21-22 typically

 

20MPH from the 1/8th to the end of the 1/4.

 

~ 24 mph

 

I only gain 20 mph. I go from 85mph 1/8 to 105mph 1/4.
I need some more top-end. (maybe it's time for a cam )

 

generally, 80% of cars run 79.441 % and 79.818 % of their 1/4 mi. speed in the 8th. or an average of about 79.63%.
10% run slightly faster, 10% slightly slower.

Exa.
80.5 mph in 8th
then
average = 101.1 mph in 1/4
80% run between 100.85 and 101.33

It's not just a typical "20" or "22" mph on the second half. There's more math involved than you might think. If your % is about the same now as before, then you either lost some power throughout the band (which I doubt) or it was just a bad night to run. If your % is skewed with a high 1/8th but lower than usual 1/4 then it's PROBABLY top end loss of some sort.
A more accurate gauge of how your car ran is how the other cars there ran.

 

Sometimes if you run a faster 60-foot, and a better ET your MPH will come down some. I still have never hear a convincing explanation exactly why but I've found it to be true in many cases.

Also, if you're running quicker than ever but you end up getting near a gear change as you're going through the lights I've had experience where my MPH doesn't change at all, even though I run a quicker ET.

On my traction limited cars that don't 60-foot worth a damn I'll usually run about 22-23 MPH more, if I'm running a car that's near a 13.0 kinda time. But the faster you go, the bigger the difference will be.

Racing into a head wind or on a track that's a slight uphill can make some pretty differences in MPH. If you're running at a different track than usual then don't even bother comparing numbers from some other track- there will always be differences.

There's a lot that affects it.

 

I usually pick up around 22 mph. Stock motor w/bolt ons, 3560 raceweight.

 

I usually pick up 26 mph. 91mph 1/8 117mph 1/4 or 90mph 1/8 116mph 1/4. I hope to change that with the th400 install.
Matt