Michael
There is a formula that you can use to get an <u>APPROXIMATED ESTIMATE</u> of what you would've run in the 1/4 mile based on your 1/8 mile ET. You have to multiply the ENTIRE 1/8 ET by 1.6 something or other. I'll try & find it for you. There are different formulas depending on what mods you have, tires, NOS, etc.
There's no replacement for actually going to a 1/4 mile track but the formulas definitely work. I've gone to both type tracks several times and when multiplying my 1/8 mile ET by the right figures, my 1/4 mile ALWAYS came out just right (all things being equal that is, making all your shifts properly etc).