Alternate rear gear ratios
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2004-2007 Cadillac CTS-V General Discussion Discussion, Alternate rear gear ratios in Cadillac CTS-V Series Forum - 2004 - 2007; I have been doing a bit of research on the Getrag rear end. The CTS and the CTS-V use basically ...
  1. #1
    Rey
    Rey is offline Cadillac Owners Fanatic
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    Alternate rear gear ratios

    I have been doing a bit of research on the Getrag rear end. The CTS and the CTS-V use basically the same rear end. ALL use a ring gear diameter that measures 7 5/8 inch. The CTS uses an open rear differential as opposed to the CTS-V's limited slip. The official GM service manual pages 4-44 to 4-104 treat the CTS and CTS-V rears exactly the same, except for output flanges, which bolt to the exterior of the carrier.
    Grear ratios available are:
    3.23
    3.42
    3.73
    3.91
    My own personal feeling is that with the 3.73 first gear is too low, and I can easily cruise at a few 100 less rpm on level highways. 3.42 is what many Corvettes use, and this is the ratio I will use. Cost is about $300. Then, I will have the ring and pinon freeze-treated (sic) and Mikronited, which should be several hundred dollars more. Total cost should be south of $1000. I have a spare rear from an EBay purchase so my car will not be down for a significant period.
    My friends at TPIS (conflict of interest) will do the work.
    What I expect to get out of this is a much quieter rear with longer service life. I don't drag race or hard launch and have no illusions that this kind of change would hold up under continuous hard launches. I will keep this car long term, and to me this is a worthwhile modification.
    I asked TPIS if they thought there was a market for this kind of changeover. In their opinion, the market is very small, a mere fraction of the Corvette market.

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    04CTSVFLA is offline Cadillac Owners Connoisseur
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    Re: Alternate rear gear ratios

    I dont understand why this wouldnt at least make the rear a little stronger ie handle the power a little better without busting open.....Why not get the whole thing treated as you described. The cts-v racecar uses a cryo treated stock getrag cts-v rear from what ive read......

  4. #3
    04CTSVFLA is offline Cadillac Owners Connoisseur
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    Re: Alternate rear gear ratios

    wont the 3.42's slow your 1/4 mile/0-60 speed down? I dont know much about this stuff...

  5. #4
    Luna. is offline Cadillac Owners Connoisseur
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    Re: Alternate rear gear ratios

    I considered a change to the rear end ratio when I first purchased the car and came to the conclusion that 3.73 is probably about the perfect gear for this car, especially when one considered the overdrive gears available in the transmissions.

    Vettes are able to get away with taller rear-end ratios because they are a lot lighter. I don't think you'd want to go much taller in a V.

    Good luck to you if you opt to go down this route, but I wouldn't.

  6. #5
    2002BlueWS6's Avatar
    2002BlueWS6 is offline Cadillac Owners Fanatic
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    Re: Alternate rear gear ratios

    Quote Originally Posted by 04CTSVFLA View Post
    wont the 3.42's slow your 1/4 mile/0-60 speed down? I dont know much about this stuff...
    Rey please let us know how this works out. I completely agree with you. This car should definatly have 3.42s like the vette. The 3.73s are too low in my opinion. I find myself shifting way to early and RPMs are always real high.

    3.42s should slow her down a bit through the 1/4 but not too badly. Probably like .2 -.3 sec. Fuel economy should go up.

  7. #6
    lunarx's Avatar
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    Re: Alternate rear gear ratios

    I like this idea alot
    With a Maggie the 3.42 would make a lot of sense.

    However it's 5th gear that really bugs me.
    It's a useless gear with no acceleration & too high of RPM's for cruising.
    It's to close to 4th and too far from 6th.
    I usually just skip 5th when downshifting and upshifting.

    3.42's might make 5th a good 60-80 cruising gear and let 6th be saved for long hauls at 80+ only.

  8. #7
    V-Max Guest

    Re: Alternate rear gear ratios

    I'd go tall and then boost it. Guys running north of 650whp in a C5 like the 3.15 rear opposed to stock 3.42. Quick math considering 800 LBS weight advantage of the C5 should yield similar results with better mpg.

    Brings up a good question: are the MN12 gears the same as the Z06? Probably is, just trying to keep apples-to-apples comparison.


    Norm

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    ctsvflorida's Avatar
    ctsvflorida is offline Cadillac Owners Connoisseur
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    Re: Alternate rear gear ratios

    You guys will lose more than you think in terms of acceleration with the 3.42's because of the weight! A maggied car or heads cam car, then yes I may recommend it but N/A, no way it is better in either instance highway or around town! You wanna save gas too...it won't help that either as we have enough gears to compensate! If it helped 1 mpg on the highway only, then that would be what I would 'possibly' expect!

  10. #9
    Rey
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    Re: Alternate rear gear ratios

    I am not advocating a gear ratio change for everyone, particularly those who are concerned with 0-60 or 1/4 mile times. My full power driving usually occurs in the 30-80 mph range where choice of gears is more important. The change from 3.73 to 3.42 is not drastic. It is more of a tweak. Check the numbers below taken from Road & Track.
    I am more intrigued about Mikronite gear treatment. Check the Jan 07 issue of Car Craft. Note, Mikronite has been around for a few years and is comparatively new to the auto scene. They started working with Crane Cams, then they BOUGHT Crane Cams. So far, it has been used mostly by racers wanting a little extra edge. 6-8 rwhp gain is about what to expect. This is not much, but what is important is the friction decrease at highway speeds where hp requirements are small. With more restrictive gas mileage imposed on OEMs, I will not be surprised to see Mikronite as an OEM supplier.
    Long term I will either Maggie the car with a 122 Maggie kit (if it is ever produced) or go to a larger LS2 block, in which case the 3.42 makes even more sense (to me). While the actions I am taking do not bullet proof the rear they do make it stronger.
    As an aside, one of the factors enabling me to make this change is scoring a late-model CTS-V rear end on EBay for $200. Blueprinting this rear will take care of any latent problems such as bad bearings, seals, etc. , and will allow me to keep the OEM 3.73 for backup.
    Stock 3.42 Corvette

    1st 2.97 50 mph @ 6500
    2nd 2.07 72 mph @ 6500
    3rd 1.43 104 mph @ 6500
    4th 1.00 149 mph @ 6500
    5th 0.71 186 mph @ 5600
    6th 0.57 186 mph @ 4700

    60 mph = 1500 rpm
    70 mph = 1750 rpm
    80 mph = 2000 rpm


    Stock 3.73 CTS-V

    1st 2.97 46 mph @ 6500
    2nd 2.07 66 mph @ 6500
    3rd 1.43 96 mph @ 6500
    4th 1.00 137 mph @ 6500
    5th 0.84 163 mph @ 6500
    6th 0.56 163 mph @ 4300

    60 mph = 1600 rpm
    70 mph = 1866 rpm
    80 mph = 2133 rpm

  11. #10
    dnswallace is offline Cadillac Owners Member
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    Re: Alternate rear gear ratios

    I'm with Rey on this one. Unless one is doing a lot of hard driving, first gear is about useless; in fact, I start out in second much of the time. Keep in mind that I use the car for a long distance commuter, so I'd really like a taller gear and the 3.42s are just about right based on my past experience with other GM LT/LS six speed cars. And thanks for the research, Rey.

  12. #11
    keeksv is offline Cadillac Owners Enthusiast
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    Re: Alternate rear gear ratios

    I would hate to see you do all of this stuff to the gears only to have the crappy thin case fail on you.

  13. #12
    pmsteinm is offline Cadillac Owners Fanatic
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    Re: Alternate rear gear ratios

    Quote Originally Posted by dnswallace View Post
    Unless one is doing a lot of hard driving, first gear is about useless; in fact, I start out in second much of the time.
    Isn't the whole point of this car to drive it hard? I love waiting for some slow poke to turn off the road and then dropping into 1st when going 20mph and flooring it.

    I'd like that 3.91 final drive...but then I wouldn't get able to hit 45mph in 1st anymore.

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    Luna. is offline Cadillac Owners Connoisseur
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    Re: Alternate rear gear ratios

    I suppose I still fail to understand. New transmissions do wonders for gear-multiplication. With gear options going up to the "insane" 50% overdrive option (6th gear), what's the point of changing the differential? If 1st gear is useless (which I disagree with--hell, look at how fast you can go in it---if the redline speed was only, say, 20mph, I might understand, but not ~46mph...), wait until you get to play with 6th gear and a 3.42 differential.

    My thought would be you'd want a differential geared appropriately so that the car could "launch," which I believe the 3.73s do well for a car as heavy as the V. Once the car is moving, however, it just seems to border on pointless, based on all the gear selections we have in the transmission.

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    ryneV is offline Cadillac Owners Fanatic
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    Re: Alternate rear gear ratios

    Quote Originally Posted by Luna. View Post
    I suppose I still fail to understand. New transmissions do wonders for gear-multiplication. With gear options going up to the "insane" 50% overdrive option (6th gear), what's the point of changing the differential? If 1st gear is useless (which I disagree with--hell, look at how fast you can go in it---if the redline speed was only, say, 20mph, I might understand, but not ~46mph...), wait until you get to play with 6th gear and a 3.42 differential.

    My thought would be you'd want a differential geared appropriately so that the car could "launch," which I believe the 3.73s do well for a car as heavy as the V. Once the car is moving, however, it just seems to border on pointless, based on all the gear selections we have in the transmission.

    I agree 100%. Lowering the rpm by 100 is a giant waste of time and money. You will not see or feel a difference. In short, it sounds like some of you should by a slushbox. Most people with GM T56 m-6 3.42 gearsets end up going with 4.10's. Why, because they are a VERY close match to the factory m-12 3.42 combo. The m-12 and and 3.73's are perfect with the increased lb. of the V. BTW, it's case flex that causes failure on our diff's, not the R/P.

    Rey, your gear ratio's in your example with speeds vs. rpm are incorrect.

  16. #15
    ntechnic's Avatar
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    Re: Alternate rear gear ratios

    On my 3,900 pound 2003 Mustang Cobra convertible, I hated the 3.55's and moved to 4.10's and never looked back. I do not 1/4 mile race by the way, strictly street, canyon carving.

    WIth the heavy weight of our cars, moving from the 3.73 to 3.91 gear isn't enough change to be worth it. I want 4.11's, first gear will be a tad short, but so what, all of the other five gears will work so much better!

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