I believe that the speed is always more reliable and accurate when compared to the time for 1/4 mile runs.
Some of you have said that to get 1/4 mile time from 1/8 mile time, you...
(1/8 mile x 1.55 or 1.56 = about 1/4 mile time)
What about the trap speed?
Say my 1/4 mile speed is 100mph, then what would my 1/8 mile speed be, say for a car with a theoritically perfect flat power curve. (same torque from idle to redline)
My current guess would be 2/3 that of the 1/4 mile, but I know thats way off.

 

It's probably closer to ¾ of the ¼-mile speed; I was running between 95 and 96 mph in the ¼ last year, and my eighth-mile speeds were 74-75. But, my 60-ft times really suck - if the car could launch decent, it would likely change that relationship.
Check the timeslip in my sig, and then change the last number from 1 thru 9 to see some other vehicles eighth-&frac14 speed relationships.

Pete

 

my trap speed in the vette is close to 100mph. here are the results from my best run : (1/4 mile) - 13.66 at 101.82 ... (1/8 mile) - 8.80 at 80.12. my 60ft was 2.06. hope this helps

 

You cannot get your 1/4 mile speed from your 1/8. You just can't. I am not trying to flame but it is impossible no matter what. No math formula will answer 1/4 from 1/8, top spped, or 0-60.

 

Most 12, 13, 14 second street cars pick up right around 20 mph (give or take a little) over the last 1/8th mile. That's the best guestimate I could provide you with.

For example, last season I ran 85 - 86 through the 1/8 and 106 - 107 through the 1/4. My dad's GT ran 79 through the 1/8 and 98 through the 1/4. My old convertible ran 77 through the 1/8th and 95 - 96 through the 1/4.