Discussion in 'SN95 V6 Mustang Tech' started by coldstaindtears, Aug 1, 2005.

  1. What is the stock rear end ratio on a 2003 v6 Automatic?

    Anyone using 3.73's on an AUTOMATIC? Hows gas milage around town and highway?

    Anyone using 4.10's on an AUTOMATIC? Hows gas milage around town and highway?

    I wanna upgrade to t-lok and a new rear end ratio but dont want to kill my highway gas milage becuase thats mainly all I do. Any help would be great appreciated!

  2. I'm going to get 4.10's and I have an 2003 v6. Most people with auto's get 4.10's, but if your going on the highway alot(like you said) you should stick with the 3.73. They go at a lower RPM than 4.10.
  3. Go with 4.10s. You might lose 1-2 mpg on the highway and little or none in town, unless your driving habits change a lot (which they might :D ).
  4. I've heard that 4.10's can give you up to 7mpg less on the highway, with a V6. I also hear that getting 4.10's its like giving your Mustang a big kick in the ass and accelerate pretty damn fast. I hear you top out at like 90 though. Is that correct?
  5. The two words that stand out in your post are "I heard...". 4.10s by themselves will not give you 7 mpg less on the highway. Anybody that says so has (most likely) never had them or (maybe) drove with a lead foot after getting them. I don't know how any reasonable mod in and of itself could drop mileage by that much on the highway. My wife's 2004 V6 auto has 4.10s and runs 3000 rpm in 4th gear O/D just below 80 mph. It also was taken on a 2000+ mile road trip last spring and I didn't notice any significant drop in mileage. I doubt it tops out at 90 mph, I'd like to try it sometime and see but the public roads here are not a good place to do so.
  6. Wow that makes things seem alot more worth while :). Gas milage is basically one of the biggest factors for me, besides $, when I look into doing things for my car. I'm a college kid so money is always avaliable to constantly fill my tank, hahaha. Since your wife has the same car as me (except mines a 2003). I'm definitly going to consider going with the 4.10's if there wasn't a big drop. Would you say that these gears are a big improvement as far as acceleration over stock? How much did you pay to get them and everything installed, (I assume you when posi rear as well)? Thanks alot for your response!
  7. I bought new gears (FRPP) and T-Lok (OEM Ford) from, and the installation was $200. You can look around for a used set if you want to save some $$. One thing you will also need to do is recalibrate the speedometer. Since you have an automatic the only way I know to do so in a 2003 is with a flash tuner. Used ones run $250 and up, new ones $350 and up. Enjoy.

    BTW the improvement in acceleration over stock is remarkable, especially when the transmission shift points and pressure have been tweaked by the previously mentioned flash tuner.
  8. Stock gearing on the GTs is 3.27. It may be the same in the 7.5 rear.
  9. It is stock for all '99-'04 V6 and GT models
  10. With a flash tuner you can adjust shift firmness and gear ratios without installing a new tune, correct? I am thinking about installing gears as well.
  11. Alright I'm definitly gonna go for the 4.10's. Thanks for all your help everyone, you never let me down.
  12. just to chime in here. when i had my 4.10's i saw a 8mpg drop in milage from stock 2.73's in my 98 on a trip to Ft meyers Fla From Pittsburgh.

    30mpg down to 22mpg same trip same car.

    the next year same trip with 3.73's and addition of an 11 psi procharger returned 26mph.

    4.10's do get worse milage. anybody that tells you otherwise is full of it. if there was little difference then why don't they come stock with them?

    3.73's are fine for an auto and are really all you need for the street. leave the 4.10's to high revving race engines and 4x4 rock crawlers. either up high hp or low torque is their best place. everyday midrange power needs ( a mix of both hp and torque) is best served with 3.45,3.55,3.73 gears

    highway drone is unbearable with the 4.10's also.
  13. Hmmmmm. Now I gotta think about it again.
  14. Yeah, I can hardly bear it.

    I dropped a whopping 1-2 mpg on two 2500+ mile road trips after installing 4.10s, and none around town. Drone???? What in the world is that from??? To each their own, but my experience with them has been great, or as you say "full of it". Personally, I wouldn't want a Mustang with 2.73s, but that is only my opinion.
  15. What kind of gas milage are you getting on the highway?
  16. your machI responds completely different to gears than a 3.8 does.

    the V8 doesn't have the same highway drone as the 6 does and the 4V engine likes steep gears where they are unnecessary in the 6

    the 3.8 does get better milage with higher gears that is a fact.

    i don't believe you dropped only 1-2 mpg on the mach

    my 99 GT vert dropped 4mpg going from 3.08's to 3.73's

    4.10's gave me very little traction in my procharged 98 and poor mileage. 3.73's are much better. 3.45's were the best in my opinion but i no longer have them.

    ask anybody that has added steeper gears in anything and they will tell you they lost milage.

    in my old 2wd 74 ford with a 360 in it i gained 9mpg on the highway going from 4.10's to 3.50's. you are not going to sway my opinion based on alot of years messing with my projects and rearends
  17. Cobra i would think there would be a difference from your case in that 99+ v6s already have 3.27's in them. So there would be less of a drop in milage. If your 98 was a 5 spd then that would affect it too. I'm not saying that there wont be a decrease in gas milage but it shouldnt be as derastic as you experienced.
  18. cobra232 This isn't a thread intended to sway your opinion, and you are certainly as well qualified to report your experiences with gear changes as me. I simply didn't have the kind of drop in mileage you experienced.

    Agree that a Mach 1 might respond differently to gear changes than a 3.8L, except again my experience says otherwise. There is my wife's 2004 Mustang V6 auto which is used as a daily driver also, which has been running with 4.10s since last fall. It's dropped about 2 mpg in town, and none on the highway, essentially the opposite of mine. It was taken on a long road trip from Texas to Michigan last spring and there was no drone. The 4.10s have made it a completely different car from the stock 3.27s, being more noticeable even than on mine because of the greater difference from the stock ratio, and maybe partly because of the automatic versus standard transmission. Also very important, her car is running with a Superchips performance flash tune.

    Whether you believe the lack of mileage drop is of course up to you. Loss of traction in your 98 is largely due to combining a Procharger with 4.10s. I myself probably wouldn't use anything greater than 3.73s or maybe even 3.55s with a S/C.

    coldstaindtears I recommend getting 4.10s. You of course use your own judgement and decide based on as many opinions as you get from those who have actually had gear changes, including those of cobra232. Enjoy!
  19. 22