I have a 89 gt with stock limited slip 2.73s. I have heard that getting new gears is one of the best upgrades to do first to your car. I have heard that both are great. One site seemed to lean towards 3.55s and the other to 3.73s. I do daily highway driving and i have a manual trans. any thoughts would be great.
My opinon would be 3.73's, but either way .. 3.55's would work quite well too, and since you do alot of highway driving, wouldn't be so hard on gas. That's just my thought though, might want to ask a few more people here .. as they are 100x smarter than I
its really up to you. you wont feel the difference between 3.55's and 3.73's. i was wondering what i should get too back in the day and the rule was 3.55 for mnual 3.73 for auto...i was worried about gas mileage too but have found it had little or no impact on it. i now wish i had 4.10's...
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-Robert
DEAD: 1994 GT (a pine tree fell on it during a windstorm...great huh)
NEW: 1995 GT Convertible, Triple Black; receiving all the goodies from the 1994 gt and some more stuff too
I'm gonna say 4.10's because I love them. I also had them on my 87 gt and the only time a stock mustang ever beat on the street was a 93 cobra and only by a fender. Of course, you will have traction problems, but anything that makes it more skilled makes it more interesting to me. With my 95 and 4.10's I still get 27 mpg on the interstate.
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97 Cobra #777 Blk/Blk
ProCharger P600B 7psi w/3 core intercooler, off road x-pipe, flows, pro kit, oil separator mod.
In 5th gear at 60 mph with a 26" tall tire (average height for a Mustang), there is only a 95 rpm difference between 3.55 and 3.73.
1873 rpms with 3.55's
1968 rpms with 3.73's
2163 rpms with 4.10
If you started with 2.73:1 gears, you will notice anything you do. I have a supercharged 306cid and I do a lot of freeway miles because I like to drive. I'm going with 3.55s, but my best bud has an 87 Vert with 342cid and NO blower and runs 3.73s. Of course, he's got a Viper 6spd, so gear ratios in his tranny are a lot different than our 5-speeds.
If you don't have a blower or plans to in the future, go with the 3.55, only because you drive on the freeway. If freeway driving is minimal, go with the 3.73s. It all depends on your driving. There is only a minor difference between the two. From a 2.73 setup, you will feel the difference immediately when you launch the first time.
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"Mad" Max
1992 LX, thanks to Chicane Sport Tuning and some friends.. it is now wrapped with new graphics and ready to hit the streets AGAIN!!!!
thanks all for the great replies. I am now considering the 3.73s more than before because in the past i heard they were no good for the highway, but it looks like they were not absolutely correct from some of your statements. Thanks again.
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1989 oxford white 5-speed gt. Mods include: Offroad X-Pipe, Flo-Pro exaust, jba headers, K&N filter, Short throw shifter, APC indiglo gauges, SPEC Stage 1 clutch, Adjustable cluth quadrant, MSD distributer, Underdrive pullies, 190 fuel pump and more.
if what jarrett has posted with the RPM's(im not questioning the numbers) im thinking about going with 4.10's myself. does anyone have any down sides to 4.10's in a 95??
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2004 Ford Ranger EDGE
1995 Ford Mustang GT
Sic vis pacem para bellum.
-If you want peace, prepare for war.
The only downside I had with my 4.10's was when I couldn't hook up, but now that I have new tires (completely old stock suspension) that is not a problem anymore and I just wanna gun it at every stoplight!
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97 Cobra #777 Blk/Blk
ProCharger P600B 7psi w/3 core intercooler, off road x-pipe, flows, pro kit, oil separator mod.
Gears: 3.55 or 3.73 
