Difference in gears?
#1
Difference in gears?
I want to run a different rear gear in a 9" rear axle. Right now it has 456 and even though I drove it mostly around town I'd like something a little better for short trips on the highway. I am leaning towards 411's but also wonder if there is much difference between 411 and something like 389? Is it that big of a step between the two? I am going to be running them in a '68 Fastback with a 4 spd toploader and a 302.
#2
I want to run a different rear gear in a 9" rear axle. Right now it has 456 and even though I drove it mostly around town I'd like something a little better for short trips on the highway. I am leaning towards 411's but also wonder if there is much difference between 411 and something like 389? Is it that big of a step between the two? I am going to be running them in a '68 Fastback with a 4 spd toploader and a 302.
#3
Easy way to tell what MPH you will be running with a certain gear is an easy math thing.
(gear ratio x 336) / (rpm x tire diameter)
eg. Assuming 26" rear tires and a 2000 rpm cruise speed.
3.89 x 336 = 1307
2000 x 26 = 52000
divide 52000 by 1307 and you get 39.78mph
4.11 x 336 = 1380 divided into 52000 gives you 37.68 mph.
3.50 x 336 = 1176 for 44.21 mph
Moving the values around in the equation allows you to find different things. I use this one because I usually have a target RPM and want to know what mph I will be traveling at that RPM.
What part of Michigan are you from? I live in the UP near Marquette. If you are up here we could work something out to get things done on your Mustang.
(gear ratio x 336) / (rpm x tire diameter)
eg. Assuming 26" rear tires and a 2000 rpm cruise speed.
3.89 x 336 = 1307
2000 x 26 = 52000
divide 52000 by 1307 and you get 39.78mph
4.11 x 336 = 1380 divided into 52000 gives you 37.68 mph.
3.50 x 336 = 1176 for 44.21 mph
Moving the values around in the equation allows you to find different things. I use this one because I usually have a target RPM and want to know what mph I will be traveling at that RPM.
What part of Michigan are you from? I live in the UP near Marquette. If you are up here we could work something out to get things done on your Mustang.
#4
It was a pain... fun on the on-ramps but that fun didn't last too long. Thank you for your reply, that helps.
#5
Thanks for the equation. I like working with exact numbers even though there always seem to be variables along the way. I live in the Grand Rapids area so that could be a bit of a drive. I'm learning as I go. I get offers around here to help but it's funny how everyone wants to be the one to put it together and nobody wants to drill out spot welds!
#6
#9
For more fun with math, you can figure cubic inch displacement with this one.
bore x bore x stroke x .7854 x number of cylinders = ci
I keep them stored in my head because I dont always have a computer handy, but I can usually find a calculator or a piece of paper..
bore x bore x stroke x .7854 x number of cylinders = ci
I keep them stored in my head because I dont always have a computer handy, but I can usually find a calculator or a piece of paper..
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musnicki
Classic Mustang General Discussion
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09-23-2015 07:11 AM