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At $3.?? a gallon I'm pulling my cash out of the bank faster than I can put it in. I know my car came with a 4.10 rear gear, will i screw anything up by installing the 3.90 out of a manny. I want just a little bit better fuel ecomony at 80mph. If anyone has any imput on how far off the speedo will be that great as well.

thanks
Ben
 

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I think your car came with a 3.9, but you can install a 3.7 from the manual, dont know how much that will be and dont know if the cost will justify potential gas savings (which wont be much at all).
 

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yes, auto's come with 3.9, manuals come with 3.7. There is an aftermarket 4.1 rear, do you have that one?

If you go from 4.1 to a 3.9, at 65 mph in 5th gear, you'll see about a 266 rpm drop. Not much if you ask me. Plus a final gear with all the necessary seals, etc will be $100-200 plus $200-300 for installation. And you'll lose some acceleration with the lower final gear ratio as well.
 
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