I just found this online and thought it may be useful:

Use this to convert 1/8 mile times to 1/4 mile times.
1/8 mile ET X 1.565 = 1/4 Mile ET
1/8 MPH X 1.25 = 1/4 MPH

If you want to, you can convert 1/4 mile times to 1/8 mile times by dividing your time by 1.565

 

damn, wish i had a time slip laying around so i could try it out

 

hey that will be usefull when i actually get to the track this spring lol

 

that is good for aproimation but when some people run the 8th they run a much low gear that wouldnt work to good in thr QRTer to well. for instance if you run a 4.56 in the 8th a lauch in 2nd and only have to shift once you cant do that in the QRTer.