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Thread: Changing rear gears?

  1. #1
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    Changing rear gears?

    Hi, I joined here years ago but never posted much, but I have a question. For the first time I took my 55 to a *sort of* dragstrip. Sort of meaning while closed and out of business they sold the tree and all timing and electronics but plan to get it again in the spring.

    Anyway right now it's sort of what they call "street racing". A flag man and an orange cone at 1/8 mile LOL. I don't get much traction but I did manage to beat a vet! (and lost 4 others). OK so I sort of feel like this could be fun, so I'm thinking of changing my 3.42 gears to 4.11 or maybe go further. The thing is that I also like cruising on the interstate at 75-80. So I'm thinking of getting some slicks that are about 28" and street tires 275/70-R16 to keep the rpms down on the road. Any comments/suggestions if this sounds like a good plan or not?

    The motor is a 454 that runs pretty well. Never dyno'd but the guy who helped me pick out parts when I rebuilt it said maybe 500 torque and 450HP. Thanks

  2. #2
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    You're not gonna like the 4.11s an the interstate and you will probably there more than you are the race track. I don't think you can put enough tire on the back to get the rpms livable cruising at 75-80mph.

  3. #3
    Registered Member zbad55's Avatar
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    Racing and cruising don't really work well together, you can always just change the pumpkin at the track to the 4.11 and then change it back when not racing. I know a few guys that used to do this in the old days.Just carry the extra pumpkin in a 5 gallon bucket,

  4. #4
    Registered Member chevynut's Avatar
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    Go with the 4:11 gears and get an overdrive transmission. Best of both worlds. Tires aren't going to get you what you want.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


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  5. #5
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    According to the Wallace racing calculator, my current set up is (255/60-15 tires)
    3000 rpm
    3.42 gear
    27.05" tire = 70.62mph

    And with a 275/70-16 at
    3000rpm
    4.11 gear
    31.16" tire = 67.69mph

    That's not too bad. But I don't know what a tire like that will look like on my car?
    My rear is a 12 bolt so no simple pumpkin change.

  6. #6
    Registered Member zbad55's Avatar
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    OK, 12 bolt=no quick change rear end. As for tire size when I was running 15's, the largest tire I could get to fit my 55 was the 255/60/15. Not sure how your going to run a 275/70/16, I dont think you fit that diameter in the car

  7. #7
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    Quote Originally Posted by chevynut View Post
    Go with the 4:11 gears and get an overdrive transmission. Best of both worlds. Tires aren't going to get you what you want.
    Yes that would be great. I may be looking at pull-a-part for a 4L80E. I don't know if they disappear really fast?

  8. #8
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    Quote Originally Posted by zbad55 View Post
    OK, 12 bolt=no quick change rear end. As for tire size when I was running 15's, the largest tire I could get to fit my 55 was the 255/60/15. Not sure how your going to run a 275/70/16, I dont think you fit that diameter in the car
    I had 275/70-15's on it and around corners they rubbed on the shackle around the springs, so I cut off the outside part of the shackle and left it on the inside. Or they may have been 265/70-15? Getting those or my current tires on/off requires disconnecting the rear sway bar and jacking it up by the frame. Actually since I added Caltracs, I just left the sway bar disconnected. The Caltracs do almost as much as the sway bar did.

  9. #9
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    I have a 74 Z28 with 3.42 Super T10 and 255/60/15s and a 67 Camaro SS 350, Super t10, 4.10s and 275/60/15 they both suck @70mph. I built a drum to drum 12 bolt with a 3.07 gear for last years Power Tour. Now my performance sucks . Unless you go with 44 inch tall super swampers gears dont cut it alone. My 56 with a 3.42 57 Olds, 700R4 or 55 with a 3.54 Dana 60 and a TKO600 both run 70 effortlessly, however no matter what you do they are shoeboxes,

  10. #10
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    If you go to taller tires that negates the gear ratio, unless you have one pair for the street and another pair for the track. Either you put up with the 4.11s with your current trans or go to an overdrive trans.

    As suggested, 31" tall tires won't fit your car no matter the width.

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