mathmatical gear ratio question

[jenavet]

this question is for any of you mathmatical/engineering types.....

if i have a car that has a 4.86 rear gear ratio..a 32 inch tall tire...and crosses the 1/4 between 7100-7200 rpms at 131.78 mph.......what rear gear ratio would i have to install in this car to get the rpms up to 8100-8200 through the 1/4 mile??

 

[Mac]

jenavet, I'm not sure I understand the question. Does your car already make the 8000+ RPM but you run out of track before you reach those numbers??

-Mac

 

[Mac]

Give this a try!!

http://www.csgnetwork.com/gearratcalc.html

-Mac

 

[Rowdy1]

Just A Guess

I don't think 5:14 would do it, you may have to go with a 5:88.:confused

 

[jenavet]

its a destroked 350 chevy...3.300 stroke with aluminum rods etc.... on the chasis dyno,the motor still had not hit peak horsepower at 7900 rpms and the horsepower curve was still climbing.....down the track,the car is only turning 7100-7200 through the traps and thats when the torque curve levels off but not near the peak horsepower..i called 3 differential companies today and no one had a clue...they make several ratios that may work...5.29...5.43...and 5.67......and for 1500.00 for a center section,i dont want to make the wrong decision....but from what i can figure with crude formulas,it looks like the 5.67

 

[jenavet]

actually mac...that calculator you gave me said 5.64...so that matches up to what i was figuring...thanks alot!!!!

 

[Mac]

No problemo. Glad to be of service!!

-Mac

 

[MaineShark]

Current Ratio, divided by current RPM's, and then multiply the result by the desired RPM's.

It all depends on which numbers you use as your current and desired rpm's, but the results all hover near 5.54:1, with your ranges.

Joe