1/8 mile convertion to 1/4 mile

rdorman · #1 (**permalink**) 06-24-2003, 08:22 AM

If you have never been down the quarter mile but timed your 1/8 mile run at DVSFIII multiply that time by 1.5832 to estimate your quarter mile.

For instance my time was 7.6 seconds in the 1/8 so 7.6 * 1.5832 = 12.03

Rick

frankym · #2 (**permalink**) 06-24-2003, 12:11 PM

your formula might work for your car but it will not work as a rule, or even a rule of thumb. For example, I was at the drag strip 2 months ago and made a pass with a CSX with a side oiler, we were dead even up to the eighth but by the end of the quarter, he got maybe 5-6 car lengths in front of me. My time in the quarter was 12.8 and he was 12.3, my speed was 110, his was 121. The gist of this is that the computation is non linear, meaning that acceleration is not a straight line, it's a curve. So, your formula, if it were to be used as a rule of thumb, would be accurate within maybe +/- a full second, but that 1 second translates to as much as 20 mph, which would be like comparing a 1987 stock mustang gt to a stroked 392 cobra replica, just not close enough to make a meaninful estimate. I'll bet though that there is a software program that can estimate performance given the facts about the engine, transmission, hp/tq and weight, but the only way to know is to go and race, it's way more fun to do it the old fashioned way! jelous that I couldn't make it to the fling!

rdorman · #3 (**permalink**) 06-24-2003, 12:20 PM

I forgot to mention that it is a 'guestimate'.

But it is fun!

Rick

BB427 · #4 (**permalink**) 06-24-2003, 12:24 PM

It is actually close for my Ford Probe, 4.82 1/8 and mid 7.60 in the 1/4 but it will not work most of the time and the MPH will never work. If you want to get an idea go to NHRA website and look at the index for stocker classes. It will give you the index in 1/4 and 1/8 mile.

Frankym your right, it all depends on the car,torque curve,gear ratio,and the diff between torque and HP.

Fun to play with though.

frankym · #5 (**permalink**) 06-24-2003, 12:58 PM

one other thing, you have to remember that the elapsed time in the 1/8 included your initial reaction time, which by itself can vary between 0.1 and 1.1+ seconds, which would wind up being distorted by a factor of 1.5832x if you stuck to the formula.

BB427 · #6 (**permalink**) 06-24-2003, 01:02 PM

Actually your reaction time has no effect on ET. The timer does not start until the front tire rolls enough to break the beam.You can sit at the line for 30 seconds before you launch, you will have a 30 second reaction time ($hit) but the ET will be the same.

rdorman · #7 (**permalink**) 06-24-2003, 01:23 PM

....... that is one thing I love about this place. If some one says it is sunny, we would debate it!

Thanks for the NHRA tip. According to their site I just broke into the 11's! http://www.nhra.com/stats/indexes_ss.html

I was able to lauch at nearly 3500 RPM. On my BFGs any thing over a very careful 1500 would fry them for ever. Love those TD's

Rick

frankym · #8 (**permalink**) 06-24-2003, 02:10 PM

I never knew that reaction time wasn't calculated into the total time! Oh well, maybe I would have found that out if I'd drag'd more than once. I guess reaction time only counts when you bet the guy next to you who would cross the finish line first! I just copied those ETs from the NHRA site, and if you take the high and low of the coversion rates, you get a high of 1.590909 and a low of 1.530278 which tells us 2 things:

1. There is a difference of .48 seconds ET between the hi/lo conversion rate on a car that does the 1/8 mile in 8 seconds, and

2. I have too much free time!