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Rear gears - tough to decide…

6

67resto-coupe

Member
swapping from original 2.79s to EITHER 3.25 or 3.40 or 3.55
only seems to be about 130rpm difference between each "level". i have a 25 mile round trip to work which is about 65/35 hiway/city. I'm really leaning towards 3.40, as it's the middle ground between a conservative 3.25 and an aggressive 3.55. True-Trac, too, by the way. 265/40-17 rear tires on 17x9.5 wheels. i already get crap mileage, so that's not necessarily the main concern..mostly the highway revs, as i can do a fair amount of highway driving on weekends for fun.

any thoughts?
 
Might be helpful to know what transmission you are running? Do you possibly see yourself upgrading to an OS transmission in the future? Or you may already be running one.

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Need to know all the gearing through the drive train to give a good answer. If you have an overdrive transmission you can get away with a lot more rear gear on the highway, for example. The ratios mentioned are mild compared to what you can run with a 5 or six speed and maintain a decent RPM at 70 mph.
 
I run a 3.50 rear end with a T5 transmission. Plenty of acceleration off the line and the car just calms down and cruises nicely at 70mph in 5th gear. I would not run gears as steep as 3.5 or greater without an overdrive transmission.
 
With a C4 I would go 3.00 but not further / higher (number wise) in rear end gears.
Maybe 3.20 but all comes how you would use the car.

I personaly have a T5z trans with 3.55 truetrac gears in the rear.
3.55 because I have then an overdrive gear.
 
3.25 is an good all around non overdrive gear... that said, I put 3.55 in my chebby and like it a lot, but don't like it if I want to keep up with freeway traffic and keep the RPMs at or under 3K.

3.25 would be my choice if I spent more time on the freeway versus city...
 
My trans is the C4. I'm considering an AOD or Gear Vendors, but that would be a ways off, as I'm fronting a lot of money for gears, interior, audio and little bits here and there.
Considering this is mainly a weekend/pleasure car, I think I'll opt for 3.40. Anything over the 2.79 will be night and day, but I do have to occasionally travel on the local highways, so my logic says the 3.40 is the lesser extreme to the 3.55. thanks all!
 
Here's an example of a calculator to help figure out what you want. A stock C4 has a 1.00 gear ratio for this calculator's purposes.

http://www.corral.net/tech/gearcalc.html

Your engine speed at 70 would be approaching 3200 rpm with the 3.40 gear. High in my opinion for anything over a short run.
 
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