Switched to 3.73 gears and not loving it

Discussion in 'High Performance Modifications' started by sinnyz_me, Jul 7, 2018.

  1. ZEN357

    ZEN357 Veteran Member

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    I would say it's your Transmission not having an overdrive gear. Swap it out for a TCI Super Street Fighter 700R4 with over drive. You'll get better driveability.
     
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  2. ajmrider

    ajmrider New Member

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    At your hp level, a 4l60e would be fine, and junkyards are full of them. Go pick one up and put a rebuild kit in it (or have a good shop do it for you) and it won't cost anywhere near 4K, and you'll have a modern, electronic (tuneable) overdrive trans. There are several companies that make affordable controllers for them. I went this route on 2 of my cars, but went with 4l80's due to high hp levels. With good quality rebuild parts, Transgo HD2 kit and electronic controller, I probably have $2500 into a rebuild.
     
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  3. NYH1

    NYH1 Veteran Member

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    Don't sound to good.

    NYH1.
     
  4. jeff swisher

    jeff swisher Veteran Member

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    It's a 3.2 mega pixel sony cyber shot camera from the 1990's that has a video function and the wind noise inside the truck is Horrible.
    Easier to watch with no sound.
    I ran it at the track many times and that engine ended up in my 57 chevy. recently got a different cam. an old Norris 288 hydraulic.
    With the cam in the video the truck ran only 2 tenths different shifting at 5500 or at 6500rpm.
    On the wheel dyno it made max HP at 5700rpm.
    Tiny cam
     
  5. NYH1

    NYH1 Veteran Member

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    Wasn't referring to the video quality or wind noise.

    NYH1
     
  6. K1ng0011

    K1ng0011 Veteran Member

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    If you have a Windows computer I highly suggest playing around with the gear calculator program below it can teach you a lot. You can put in different tire sizes, rear end gear ratios, and transmission gear ratios. Once you play with it enough you will get an idea on what will give you your desired rpm at what mph. There is a few questions you need to ask yourself though. You need to know your tire size, what transmission you have, and what the highway speed is in your area. Some areas in the US have highway speeds of 60mph and some have a highway speed 70mph for example. I have found this program to be fairly accurate within a few hundred RPM. It only cannot account for weight and aerodynamics. Overall first gear ratio is first gear in your transmission x rear end gear. From what I have read you really want a rear end gear between 8.0-10.00. Higher the number on your overall first gear ratio the harder your launch. Anything under 8.0 is going to be pretty slow. I have ran a 2.73 Rear End with a Th400 with an overall gear ratio of 6.77. That thing was pretty slow with a stock 350 engine. However you can compensate for poor gearing with a lot of torque so if you running a 600HP/TQ big block having a lower gear wont matter as much. I have put some examples below using the gear calc program to give you an idea of what kind of differences you see by changing you rear end gear. If you plan on keeping your three speed transmission you probably going to find the gear that will give you the both of best worlds between 3.23 and 3.43. Also something to keep in mind is from what I have seen anything below a 2.73 gear does not get a lot of after market support. Take some time look over all of the information play around with the program and you can find what will work for you. I run a rare overdrive 4 speed manual trans. The first gear in the trans is higher than most transmissions. This allows me to run a lower rear end gear and keep better acceleration. So I can cruise at 60MPH and 80MPH at about 2100RPM or so. I took my time to figure out what worked for me and I am happy with it best of luck.

    What Transmission?:
    What Highway Speed in Your State/Country?:
    What is your tire size?:
    What cruising RPM are you comfortable with?:
    Making enough HP/Torque to overcome poor gearing?:

    Gear Calc Program: https://locost7.info/gearcalc.php

    Chevy Automatic Transmission Gear Ratios: http://www.oldengine.org/unfaq/leadfoot/trans.htm
    TH350 Gear Ratios: 2.52 1.52 1.00
    TH400 Gear Ratios: 2.48 1.48 1.00

    Example Setup w/TH350
    225/70R14, TH350, 2.41 Rear End = @70MPH/2148RPM, @60MPH/1841RPM, Overall First Gear Ratio: 6.073
    225/70R14, TH350, 2.73 Rear End = @70MPH/2433RPM, @60MPH/2086RPM, Overall First Gear Ratio: 6.88
    225/70R14, TH350, 3.08 Rear End = @70MPH/2745RPM, @60MPH/2353RPM, Overall First Gear Ratio: 7.762
    225/70R14, TH350, 3.23 Rear End = @70MPH/2873RPM, @60MPH/2468RPM, Overall First Gear Ratio: 8.140
    225/70R14, TH350, 3.43 Rear End = @70MPH/3057RPM, @60MPH/2620RPM, Overall First Gear Ratio: 8.644
    225/70R14, TH350, 3.73 Rear End = @70MPH/3324RPM, @60MPH/2850RPM, Overall First Gear Ratio: 9.400
    225/70R14, TH350, 4.11 Rear End = @70MPH/3633RPM, @60MPH/3140RPM, Overall First Gear Ratio: 10.357


    My Setup
    Transmission: NP440/MY6 - 1st 3.09, 2nd 1.67, 3rd 1.00, 4th 0.73
    Tires/Wheels: 225/70R14
    Rear End Gear: 2.73
    Speed @80MPH - 2030RPM
    Speed @70MPH - 2433RPM
    Speed @60MPH - 2086RPM
    Overall First Gear Ratio: 8.436
     
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  7. Evil Twin

    Evil Twin Veteran Member

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    The first thing I'd try is a taller tire but if you have your heart set on changing the gears I'd go mid 3s. As far as transmissions go a T-400 isn't going to help but it's the strongest trans out there.
     
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  8. John Wright

    John Wright Veteran Member Lifetime Gold Member

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    I'm running 3.73's in my 12 bolt with a 275/40/17 tire and T-56 transmission.
    [​IMG]
    That is about 1700 rpm at 71.1 mph
     
  9. mallard

    mallard Veteran Member

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    My '74Z T10 4sp came originally with a 373 rear. I've had it 34 years and the immediately previous owner switched the 373 to 355's. The tac shows right around 3000 @ 60 mph.
     
  10. 351maverick

    351maverick full time Ebay seller/hustler/car killer

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    I don't ever understand these kind of threads.....4k rpm isn't hurting ANYTHING...believe it or not these motors were meant to RUN, not idle down the road which is what everyone seems to want lately
     

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