for those who can't decide 3.55 vs 3.73

Discussion in 'Fox 5.0 Mustang Tech' started by remat457, Jul 29, 2004.


  1. mob

    mob the guy who hits on his mom

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    3.55 vs 3.73?? i was always having trouble between 3.73 and 4.10 im going with 3.73's i think it takes a special person to like 4.10's id rather stay on the safe side and just go with 3.73
    #21
  2. drgn5.0

    drgn5.0 Founding Member

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    4.10s here baby!!!

    gonna to keep them with the turbo too.
    #22
  3. Michael Yount

    Michael Yount Advanced Member

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    drgn - that turbo is gonna make more torque across the board - general rule of thumb is to take a bit of gear out of it and let the boost/torque do the work. But you can always make that decision later.
    #23
  4. jmuva44

    jmuva44 Founding Member

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    I suggest nothing lower than 3.73s for any bolt on car. 3.55s are a waste of money. I went from 2.73 to 4.10 in my AODE 1995 GT. It made a WORLD of difference and gas mileage dropped very little. If you are thinking of getting gears and are either not going to do them or are going to do them conservatively because of gas mileage....dont even let that bother you. It doesnt drop much at all. Also if you are worried about traction then you shouldn't be driving a rear wheeled sports car with a V8. Same arguement can be said for the gas mileage.

    I think the standard everyone goes by is how it should be:

    5spd...........3.73 gears
    AOD(E)/Vert..........4.10 gears
    #24
  5. 67GTCOUPE

    67GTCOUPE Founding Member

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    I have 2.73's in our 94 Vert......it is a dog, but I am worried about going to 3.73's due to the possible need for an aluminum driveshaft, plus I ??will?? need a new spedo gear?

    What is the deaL?
    #25
  6. jmuva44

    jmuva44 Founding Member

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    No need for a new driveshaft. And no, you wont need a speedo gear but you will rack up extra miles and your speedo will be way off if you dont.

    I'd really consider putting 4.10s in there. Gears are not as scary as you think they are.
    #26
  7. Michael Yount

    Michael Yount Advanced Member

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    Any numerical increase in gear ratio results in the driveshaft spinning faster. The amount of the increase is the same as the ratio of the gearing - 3.73/2.73 = 1.366, about 37% faster. Any small imbalance in your driveshaft that was present before will be magnified due to the increased shaft speed. Beyond that, rotating columns that are transmitting torque have other dynamics that can cause vibration - they are a function of the length of the column (shaft), the wall thickness of the metal and the speed. As a practical matter, you won't know what yours is gonna do until you put the gear in - no way to predict it. So, the deal is - Yes, you might have to make a driveshaft alteration, and Yes, if you want your speedo to be accurate you'll have to make a speedo gear adjustment. Part of the deal.
    #27
  8. TT91

    TT91 New Member

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    As cool as that may sound, it doesnt make u a badass, it makes u a dumbass, sorry to be so blunt, but your going to want/need to run something lower then a 3.55, most likey a 3.27 with that turbo...

    www.Turbomustangs.com is your friend
    #28
  9. 67GTCOUPE

    67GTCOUPE Founding Member

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    OK......possibly going to 4.10's in a 94GT vert.....would I need a chip? or can I just get a new speedo gear???

    Thanks
    #29
  10. TT91

    TT91 New Member

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    New speed gear. :nice:
    #30
  11. Michael Yount

    Michael Yount Advanced Member

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    Speedo is cable operated in the 94 - speedo gear does the trick. Now a chip would help with that pesky 94/95 ecu.....
    #31
  12. RydeOn

    RydeOn Licensed to Chill Founding Member

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    Ehhh....the correct way to approach this is hardly a "screw it, just do it" mentality. You need to put some more thought into choosing gears besides 3.73's for 5 spd or 4.10 for AODs. 3.55's are not a "waste of money" for a light foxbody. Steeper gears do not make your car faster. Adding power makes your car faster. The gears need to be matched to the powerband. There are plenty of 3.55 cars that will rip a 3.73 car in a race.
    #32
  13. Michael Yount

    Michael Yount Advanced Member

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    RydeOn hit the nail on the head - with one exception. Many cars are geared so long for fuel economy, that steeper gears not only maket them quicker, but faster too. The reason is that for cars like our 5.0L's, the 2.73 gear won't let the engine come anywhere near the power peak in 5th. A set of 3.55's or 3.73's let's the revs come up so that more of that power band can be accessed when nearing top speed. It's the same reason that a new Corvette reaches top speed in 5th gear, rather than 6th - perfect example of more gear making a car quicker and faster.
    #33
  14. jmuva44

    jmuva44 Founding Member

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    Never said that gears make you faster. They actually make you slower if you wanna be technical. They do accelerate you quicker however which many percieve as going faster. So you are partially right. Oh well.

    Also if you do a search on gears, most that have 3.55s with a bolt on only NA car regret not going higher. Do the search, you'll see. I did the search when I was looking into gears. Thats why I say they are a waste....you most likely only want more. Thats also why I say not be scared of the gear. You will be happy you werent conservative. Now if you plan on going the power adder route or big head/block route, yes 3.55s may be more suitable. For the most part, although some won't, most will agree that 3.73s for 5spd and 4.10s for AODE is most appropriate and satisfying for the majority of bolt on stangers. I've had 3.73s twice now in two bolt on 5spds and 4.10s in my AODE and they were very balanced. If anything, I still wanted more.

    Most people do not need a driveshaft either. Some may if the stock one is already whacked. I'd be willing to bet, if you dont have any vibration issues now, you wont with gears.

    With an AODE you will not NEED a chip but you will greatly appreciate one. My AODE with 4.10s was hitting the rev limiter fairly easily and the transmission shift points were needing adjustment because with the gears the trasmission shifted too quickly.
    #34
  15. Michael Yount

    Michael Yount Advanced Member

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    "They actually make you slower if you wanna be technical."

    Not so most of the time Chris. More numerical ratio only makes you slower if you're redline limited already. VERY FEW cars are redline limited - they're aero limited. In the Stang's case, because the combination of top gear in the tranny and the stock rear ratio is so long (.68 in the tranny for most, 2.73 rear), the car won't come close to accessing peak power in top gear. So it simply runs out of steam somewhere in the mid 3000's. As mentioned before, it's just like the new Corvette's. Their top speed is achieved in 5th, not 6th, because 6th is just too long to pull up to peak revs. Downshifting the Corvette into 5th allows access to the higher part of the power curve allowing more speed to be achieved. Same thing happens when you put some more gear (within reason) in the back of a stock or mildly modded Stang. More gear (3.55, 3.73) = faster or more top speed. Now when you go steeper than that, you may start to run into being redline limited.
    #35
  16. jmuva44

    jmuva44 Founding Member

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    Maybe I'm wrong but dont gears limit top end? Kinda like a 10 spd where if you are in the big gear all the time, the bike eventually (disregarding other factors) tops out? When I had my 4.10s installed i lost a LOT of top end. On the highway it had absolutely nothing to offer. The RPMs just ran out. Maybe I'm wrong here.....
    #36
  17. Michael Yount

    Michael Yount Advanced Member

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    Chris - more rear gear limits top end if you're redline limited already, or if you put a lot of gear in. But that's not the case in most cars. Mentioned it before - Corvette has to downshift from 6th to 5th to reach it's top speed. Most Stangs who go from 2.73's to 3.55's or 3.73's will see an increase in top end - cause they can now get the engine speed up in the rpm range where it's making more power.
    #37
  18. jmuva44

    jmuva44 Founding Member

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    Well isnt 6th gear an overdrive gear anyways? If so then yeah, you would have to downshift to get higher speeds.

    And yes with more gear you get to the powerband quicker but you also go thru it quicker. The AODE being the worst case cuz its controlled to never touch the power band.
    #38
  19. Michael Yount

    Michael Yount Advanced Member

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    5th is overdriven in the Vette's tranny too Chris. That's the point - a downshift is the functional equivalent of a bigger rear gear. Sometimes a bigger rear gear means a higher top speed, not lower.
    #39
  20. jmuva44

    jmuva44 Founding Member

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    Well I think the corvette has more RPM and power to play with than the Mustang. All I know is that my poor little Mustang was too wound up when I was on the highway. Downshifting woulda only made matters worse.

    *EDIT* I installed a GT40 intake afterwards and it helped a LOT with the top end.
    #40

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