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    Results 1 to 11 of 11
    1. #1
      Join Date
      Feb 2011
      Location
      dallas, tx
      Posts
      1,729
      Country Flag: United States

      Ford 9" rear ratio discussion

      67 camaro , t56 magnum 2.66 , ls3 447rwhp, 315/30/18 rear tire (25.44") Ford 9inch

      4 or 5 times a year autocross, weekend fun car

      Currently have 4.11s and I was thinking about switching to a 3.70 or 3.90 gear. 4.11 are a blast but I would like to lower the highway rpms down slightly but don't want to lose to much of my 2nd and 3rd gear around town pulls. Not alot yoy can do in 1st and 2nd gear goes by quick .

      What do you suggest? Will I notice a difference with going to a 3.90 or should I drop down to 3.70s?

    2. #2
      Join Date
      May 2010
      Location
      kitchener,Ontario,Canada
      Posts
      2,336
      Country Flag: Canada
      Google rear gear calculator ....plug in your above info , it will spit out what your now new cruise rpm would be . Actually maybe even go to tremec website
      Spinnin'my tires in life's fast lane

      Ryan Austin
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    3. #3
      Join Date
      Dec 2010
      Location
      Fredericksburg, VA.
      Posts
      3,155
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      I'm running an old school SBC, close ratio T56 Magnum, Moser 9" floater with 3.89 gears and 27" tall rear tires. This setup is just about perfect for my driving. Some around town and some highway and it is good at both. Tremec has a nice gear ratio calculator that is pre-programmed with their transmission ratios that is very helpful in playing with different rear gears.

      http://tremec.com/calculadora.php
      Steve Hayes
      "Dust Off"
      68 Camaro

      Given sufficient initial acceleration, even pigs can fly!

    4. #4
      Join Date
      Feb 2011
      Location
      dallas, tx
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      1,729
      Country Flag: United States

    5. #5
      Join Date
      Feb 2011
      Location
      dallas, tx
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      1,729
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      Quote Originally Posted by TheJDMan View Post
      I'm running an old school SBC, close ratio T56 Magnum, Moser 9" floater with 3.89 gears and 27" tall rear tires. This setup is just about perfect for my driving. Some around town and some highway and it is good at both. Tremec has a nice gear ratio calculator that is pre-programmed with their transmission ratios that is very helpful in playing with different rear gears.

      http://tremec.com/calculadora.php
      Thought you ran a 335/30/18? 26" tall tire

    6. #6
      Join Date
      Feb 2016
      Location
      Lawrenceville, IL
      Posts
      348
      Country Flag: United States
      If you're building the car for mainly just street/highway driving I would go with the 3.70 to get you the best cruising RPM. You still have plenty of power to have fun with that gear set. Plus on the autocross you'll be able to stretch first gear out a little longer which , depending on the course layout, may be a good benefit. If you are torn, when it comes right down to it, there's really only a 200 RPM difference at 65mph between the 3.70(2000rpm) & 4.11 gears(2200RPM) Do what makes the most sense for the majority of the driving you will be doing.
      visit us on the web at www.bowlertransmissions.com

    7. #7
      Join Date
      Apr 2001
      Location
      The City of Fountains
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      15,971
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      My preferred rule of thumb for rear end ratios is between 2000 and 2200 RPM at 75MPH. That said, I really noticed when I went from 3.73s to 3.42s in my GTO. It got nicer on the highway but there is noticeable loss of pep off the line. The 1/4 mile times also reflect this. Then again, it's 4000 pounds with me in it and YMMV...

      Andrew
      1970 GTO Version 3.0
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    8. #8
      Join Date
      Jun 2001
      Location
      Orlando, FL
      Posts
      10,603
      Country Flag: United States
      My starting point is 3.25 (9" Ford) or 3.28 (8.8" Ford).



      I don't see the need for wicked fast acceleration from a standing start, and, in fact, I think killing some low-end torque is desirable to keep the rear tires behind you while driving in anger on a racetrack. 3.25 gears allow the use of 2nd gear on low-speed corners, 3rd on mid-speed, and 4th on big sweepers with room to get north of 140 on long straights.
      John Parsons

      UnRivaled Rides -- Modern upgrades for your ride.

      UnRivaled Rides recent project -- LS9-powered 69 Camaro


    9. #9
      Join Date
      Dec 2010
      Location
      Fredericksburg, VA.
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      3,155
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      Quote Originally Posted by icemanrd19 View Post
      Thought you ran a 335/30/18? 26" tall tire
      My bad, you're correct 26" rears.
      Steve Hayes
      "Dust Off"
      68 Camaro

      Given sufficient initial acceleration, even pigs can fly!

    10. #10
      Join Date
      Feb 2011
      Location
      dallas, tx
      Posts
      1,729
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      Love the 3.70 gears. 2200 rpms cruising 70mph is quite and more relaxing. Driving around town in 4th or 5th going to speed limit keeps the rpms down as well. Didn't feel any real loss in 2nd and 3rd gear taking off. Allows the tires to grip alittle better before breaking them loose.

      Now I need more power! Thinking about going with a fast intake

    11. #11
      Join Date
      Jul 2011
      Location
      Nashville/ Tampa
      Posts
      724
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      Quote Originally Posted by parsonsj View Post
      My starting point is 3.25 (9" Ford) or 3.28 (8.8" Ford).

      I don't see the need for wicked fast acceleration from a standing start, and, in fact, I think killing some low-end torque is desirable to keep the rear tires behind you while driving in anger on a racetrack. 3.25 gears allow the use of 2nd gear on low-speed corners, 3rd on mid-speed, and 4th on big sweepers with room to get north of 140 on long straights.
      This is what I just put in mine, partly for the reasons you stated and partly because I got a good deal on a new Strange 3rd member that happened to have 3.25 gears in it. I have the wide ratio T56, and with the previous 3.73 in the rear 1st gear was nearly useless. Might be a bit slower off the line, but since I can hold gears longer there is less shifting when cruising around town and ultimately it's probably a wash. 80-85mph on the interstate is cake, too.
      https://www.instagram.com/gen_v_lt1_chevelle/


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