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I was looking at rebuilding the rear end of my '06 4.0L, put in a limited slip and some 3.73s. My question is how will this new gear ratio effect my performance at higher speeds? Should I expect to obtain a lower top speed and by how much? Also for high way driving I've been told that at 60mph I should be around 2,000 rpm in 5th rather than my current 1,500 rpm in 5th, does that sound about right?

The idea of giving my car a real launch with these gears sounds great but I would really like to know how they will effect my performance at higher speeds first. Thanks for any insight anyone can provide!
 

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I can't help with the gears and top speed (as I have not done this mod, or looked into it).

But as forr the 60 MPH (100 KPH) 2000 rpm thing, it's not true. 2000 rpm is a generalized 'sweet' spot for your engine (getting the best power for gas usage) which is why most people try to drive at that point on the highway. Unfortunately this spot does not line up with the max speed limits in Canada and is usually closer to 120 KPH, which is closer to the speed limits in Michigan (70mph). But in the end all you are hurting is your gas consumption in the end so it's not that big of a deal.

Hope this helps with at least half your question.
 

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its not going to affect your top speed, the top speed on our cars is not even attainable. theoretically our car should reach redline in 5th gear somewhere around 200 mph i beleive? we dont have nearly enough power to overcome the wind resistance that doesnt allow us to get there. (not sure on the exact theoretical top speed, but i know we cant reach it) even with 4.10's you arent going to get to redline in 5th so dont worry about losing top end speed.

gears are designed to wind through the gears faster, and get you in the power band of your car quicker, making the illusion of power, and boosting your acceleration.

yes, if you got like 4.70 gears, then im sure you would be hurting your top end speed, but definitely not with 3.73's
 

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Discussion Starter #4
And that's what I wanted to hear ;) thanks for the help I'm thinking I'll go through and pick up some 3.73s!
 

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Assuming you have the HP to overcome all others and you have the start and stop distance: tire size and final OD ratio drive the equation.

I did a little math on this a while back. Using my nitto's and 3.73's

Drive Ratio RPM Top speed
0.79 6000 170
0.68 6000 197
 

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those gears will help at any speed, low or high...Stangs are notoriously under geared...that's why those Camaros have so much more bang 3:55s from the factory...hate GM, but they do know acceleration and handling
 
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