Super Confused… I Was Wondering What Would Be The Best Rear Gear Setup For A TH350

Posted in Perfomance Parts

Have a 68 camaro with a 350 crate engine in it I play on destroying people at lights and use it for occasional road trips up to 4 hours but it will not be my daily driver… I am currently in the process of putting a posi in it and I don’t know what rear gear I should use… thanks for your help

There are 6 Answers for "Super Confused… I Was Wondering What Would Be The Best Rear Gear Setup For A TH350"

    1. paul h says:

      3.73 gears would be a good compromise between off-line performance and periodic highway travel. Going higher to 3.90 or 4.11 gears will be a major drawback for highway travel and fuel economy from high engine rev’s and going lower to 3.55 or 3.43 gears may not give you the performance you want off the line….especially for a small block motor with less torque than a big block. Gears are not the total solution either…you’ll need a suspension and shock setup that can apply the power to the ground during launch without excessive wheelspin.

    2. John W says:

      3. 73 is a good all around gear

    3. pharm_docs says:

      You’re actually not giving enough information – specifically, is it a mild perf 350? What cam? Even more important – what transmission? What’s your converter stall (if its an automatic)

      A 3:73 is a good gear IF you have a powerglide, or a manual with a poor 1st gear. If your engine is a potent low-end engine, you’ll give up a good chunk of driveability for just a little extra acceleration.

      If your engine is radically cammed, you’ll want to get up and stay up in the higher rpm’s – there a 3:73 is a good gear to have.

      Either way, calculate what your engine will be turning at 70mph (highway speed), and you’ll see that you’ll be revving up there if you don’t have a decent overdrive trans or 5/6 speed manual.

      For my two cents, a 68 Camaro is a reasonably light car, and your 350 is more than capable of putting some good torque numbers down low. I’d petition for a 3:43 gear – it’s tall enough for some stop light action, yet it’ll give you low enough rpm’s that you’re not shaking yourself silly with an over-revving engine at highway speeds.

      Then again, if it isn’t your daily driver, you may want to think about making it a little rowdy down low – and keeping the drives a little shorter!

    4. Tim says:

      i would get a summit racing th700-r4 4 speed transmission over the 3 speed th-350 . with the 4 speed you could run a low to mid 4 rear gear and get the best of both worlds however being your only changing the rear gear .. you need to know the size of the diameter rear tires that will also affect how the gears work as speed / gas mileage . i would say a low 4’s rear gear .. there is some formulas to figure engine rpm, and at what speed .. I had a s10 with a chevy 302 th350 with a 205/60/15 rear tire turned about 2300 rpm @60mph and got about 12 miles to a gallon. when i changed to the 700-r4 it went to 19 miles to the gallon.. my advice .. call summit racing .. they will be able to figure every thing out and advise you on what gear and how it will affect horsepower/ gas mileage . ^(

    5. Mike A says:

      3.73 is the standard setup for a street car with turbo 350. This could be taken on trips but don’t count on gas mileage. If you want mileage look into an overdrive.

      Be sure to account the price difference; if an overdrive is bought for 2 grand, and this much money in gas won’t be spent over the next few years – keep the 350. The 350 has closer gears and is very cheap to rebuild.

      This also depends on the current rear gear. If you have a higher (lower #) gear than 3.70 you might want to buy the overdrive because of the more aggressive 3.06 first gear in, for example, the 700r4. It wouldn’t make sense to spend a grand on a rear gear when a grand more could be spent on an overdrive with about the same final gear ratio. Bowtie has good trannys. Hope this helps.

    6. boogie_4wheel says:

      You want 2 different things and you can only have one.
      For the 4hr trips, I would go with at least a 3.08 if not taller (if available). I had a ’70 C10 pickup running 255/70R15 with a 3.08 (yes a 350 tranny) and would turn 3000rpm at 70-75.

      I’m guessing you will be running a little bit shorter tire, so your going to loose some speed there.

      If the car is going to be driven in town more, maybe a 3.42/3.55 ratio would be a good choice. Going any lower and your gonna rip from the light, but it is going to super suck on the highway. As said by others, you may want to look at swapping the TH350 with a 700R4. Then you will have an OD gear, and this will allow you to run a shorter rearend ratio (3.73 or 4.10) and you get the launches plus some good high speed cruising.