the car is running a 29 inch tire and a 4.56 gear
what would be the RPM at the 1/4 mille light

what is the correct fomula to add this

thank you all

51.5997 mph with 10% slip at 3000 rpm.

http://www.angelfire.com/fl/procrastination/rear.html

accontrol, There is a book called the Auto Math Handbook, written by John Lawlor and published by HPBooks that is available at most bookstores and has all sorts of interesting formulas including the one your looking for. It also has all sorts of conversion tables for referencing grams, kilos, pounds and other measurements in it. The only information thats not spot on is torque converter slippage as that runs all over the place and varies with every converter. Generally tight and expensive converters give predictable results. Cheap ones generally don't. To sort of answer your question: 120 MPH with a 4.56 gear and a 29 inch tire should require 6300 RPM + converter slippage. (about 6800 RPM).

my non- calcualted guess is 6800 right where I am with a 4.33 and 26" tires.

My 67 is running 7700 RPM going thru the traps @ 132 MPH w/ 4.56's and 29 inch tires. I'm doing two things to correct it. # 1 is to tighten the converter ( calculator say I should be doing 145 MPH ) and second I'm going to drop to a 4.30 or 4.10 rear ratio to bring the rpm down.

Your answer actually depends on how much horsepower and weight you have. But, here's a site with lots of formulas.
http://murray.faithweb.com/formulas.htm#find_tire

depends on the trap speed, converter and tire construction.

According to that site onovakind67 posted, I can go 183mph at 6000 rpm in 3rd gear. :eek:
Something seems fishy...

Here is the formula for RPM, incase you don't want to use a computer every time you need to figure some numbers.

RPM = (trans ratio * MPH * 336 * rear ratio) / (tire diameter)