3.55 will give you a little kick in the pants. 3.73 will make you wish you hadn't: your gas mileag will suck and you might risk "pushing" the rpm's out of the torque range.... the higher your rear end, the quicker the car is, the less top end you get...
First of all, you won't even notice the difference if you only switch to 3.55. You MIGHT notice a little bit, but it wouldn't be worth it.
Second, the 3.73 is a perfect gear if you ask me. Despite what the guy above me thinks, you won't suffer a terrible gas mileage loss. You may even pick up a few MPGs around town since you will be able to use 5th more instead of leaving it in 4th. A 4.10 gear could even be used if you wanted. There are plenty of people that run 4.10s on the highway.
i have a 2003 mach,very similar cars,i have 410's and i found myself doing 120 on i4 without noticing.your engine respond so well to high rpm's that you won't be disappointed. now if you look at the rpm's and compare them with a 5.0 you'll think you are really revving high.but your engine is capable of 7000 or more,so is no comparison.
4.10's is a must for Cobra's or Mach 1's. The 4V loves to rev and their powerband is up in the rpms. You need something to get your there quicker and your stock gears or 3.55's won't get you there quick enough. i've had 4.30's before and they were fun in my 05 but after 6 months, i went down a little. I just ordered 4.10's for my Terminator
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1995 Mustang GT-Heavily Modded-Sold 2003 Ford Lightning-Sold 1997 Saleen-5.4 conversion-Sold 2005 Mustang GT-Torch Red-Sold 2003 Mustang Cobra-Oxford White 2003 4Runner V8 Sport Edition 4X4
im going with 3.73 any idea how much of a gas loss that is on highway? if what i hear is correct. each gear set u go up u use 200 more rpm? so as in i have stock 3.27. if i went up to 3.73 thats 2 gears up right? soo id lose 400 rpm?
I agree 2oo5GT 4.30's are too steep for the 03-04 Blown Cobra but the NA 99-01's that hit the dragstrip on a regular basis and aren't to0 concerned with Highway rpms go 4.30-4.56
Steven a bit of advice, your Tremec 3650 Tranny has a Nicer Overdrive 5th gear than the T-45 so putting 3.73's aren't gonna be bad at all for you, the 99 Cobra guys will see higher Highway rpms over the 01's!! Go 4.10's
4.10s eh? hmm i was questioning that. i mean. from 3.27 to 3.73 is a decent jump in performance isnt it? like 3.55 wouldnt be worth the money. but see. my cobra is more of a daily driver. and i dont race realy with it,(not that there isnt a few local drag comps coming up. 6 times a year !!
but wouldnt 4.10s kill my gas? or maybe not kill but hit it down a bit?
basicly. do u think 3.73 would be ok? like from what i hear itd be perfect. not TO steep but not to small.
so idk. still think 4.10?
any idea how much it cost to have em put in?(besides the gears) so just labor.
Labor 200-300, DON'T pay more than that! Any Stang performance shops where your at in Minnesota? It's ALWAYS better to have a place do it that sees this job quite often and are confident they can set your ring and pinion up with the correct backlash! 3.73's are fine but if you do mostly daily driving stop and go and see limited highway miles 4.10's!!
And they'll give you BETTER gas mileage than you have right now!
help! best rear end gears for 2001 Mustang cobra? 
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