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2nd Gen diff


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13 replies to this topic

#1 Fbird79

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Posted 04 September 2020 - 05:16 PM

Hey Im just wondering what kinda gear ratio I can put in my stock 10bolt to get more torque. Im sandblasting and powder coating it so I might aswell throw some good guts in there while its off the car. Thanks in advance

#2 ZumpTA

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Posted 04 September 2020 - 06:14 PM

If you have the 2.73, 3.23 would be a nice improvement.  3.42 is an option too if I recall correctly.  Personally, I wouldn't go higher even if I could.  3.23 is a good balance between performance and economy.


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#3 b_hill_86

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Posted 05 September 2020 - 04:33 AM

Depends on your current ratio. There are different carriers and you may need to change depending on what you have and what you want to go with.

Also depends on how you drive your car. I like the ability to drive on the highway so when I swapped mine I went from 2.41 to 3.08. I personally wouldnt ever go any numerically higher than 3.08 for any kind of highway driving unless it was only literally every once in a while.

#4 Fbird79

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Posted 05 September 2020 - 07:58 AM

I wont be doing highway driving, Im thinking more a light to light cruiser, I was thinking of 3.42 or maybe higher, Im looking for torque

#5 JoePeek

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Posted 05 September 2020 - 01:04 PM

I always thought a gear is a compromise situation. Depending on what cam you have, how much torque the engine itself makes, what is your expectation for acceleration, and of course what RPM do you want to cruise at...and at what highway speed. If you say I want to keep my engine RPM below 2300 at 70 mph, and calculate back to see what you get, and say it comes out to a 3.23, and that is a good improvement from what you have now, then OK. Or go at it from the other direction, and say I want to increase my rear wheel torque by 35%, and that maths out to a 3.73, and you don't really get on the highway that often, then that may work best. In the end, for the street, in a car you may find yourself on the highway going 70 MPH, a 3.42, or maybe a 3.55 if you want to stretch it is where I would draw the line. In a 3600 lb. Firebird with a 301 you may want to go 3.73 if you really want a big jump, but be aware that you will wish you had an extra gear if you get on the highway. With a 400 or 455 for sure, a great street gear is 3.08, but the bigger engines make more torque at the flywheel so they don't need the gear a 301 may need....it's a trade off for sure. Gears are like cams, don't go too crazy and you will like it better.



#6 Fbird79

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Posted 05 September 2020 - 06:58 PM

I always thought a gear is a compromise situation. Depending on what cam you have, how much torque the engine itself makes, what is your expectation for acceleration, and of course what RPM do you want to cruise at...and at what highway speed. If you say I want to keep my engine RPM below 2300 at 70 mph, and calculate back to see what you get, and say it comes out to a 3.23, and that is a good improvement from what you have now, then OK. Or go at it from the other direction, and say I want to increase my rear wheel torque by 35%, and that maths out to a 3.73, and you don't really get on the highway that often, then that may work best. In the end, for the street, in a car you may find yourself on the highway going 70 MPH, a 3.42, or maybe a 3.55 if you want to stretch it is where I would draw the line. In a 3600 lb. Firebird with a 301 you may want to go 3.73 if you really want a big jump, but be aware that you will wish you had an extra gear if you get on the highway. With a 400 or 455 for sure, a great street gear is 3.08, but the bigger engines make more torque at the flywheel so they don't need the gear a 301 may need....it's a trade off for sure. Gears are like cams, don't go too crazy and you will like it better.


Thank you, thats exactly what Im looking for

#7 Ponch73

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Posted 16 September 2020 - 05:52 AM

I always thought a gear is a compromise situation. Depending on what cam you have, how much torque the engine itself makes, what is your expectation for acceleration, and of course what RPM do you want to cruise at...and at what highway speed. If you say I want to keep my engine RPM below 2300 at 70 mph, and calculate back to see what you get, and say it comes out to a 3.23, and that is a good improvement from what you have now, then OK. Or go at it from the other direction, and say I want to increase my rear wheel torque by 35%, and that maths out to a 3.73, and you don't really get on the highway that often, then that may work best. In the end, for the street, in a car you may find yourself on the highway going 70 MPH, a 3.42, or maybe a 3.55 if you want to stretch it is where I would draw the line. In a 3600 lb. Firebird with a 301 you may want to go 3.73 if you really want a big jump, but be aware that you will wish you had an extra gear if you get on the highway. With a 400 or 455 for sure, a great street gear is 3.08, but the bigger engines make more torque at the flywheel so they don't need the gear a 301 may need....it's a trade off for sure. Gears are like cams, don't go too crazy and you will like it better.

 

 Very good write up Joe  :lol:



#8 EdKnecht

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Posted 3 weeks ago

I’ve had two cars with 3.73 gears, one was an ElCamino and the other was a 70 Vette. The vette was a 4-speed car...ran about 2800 at 72 mph and got about 16 mpg....I always drove a little spirited.

I love a 3.73.



#9 b_hill_86

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Posted 3 weeks ago

Ive had two cars with 3.73 gears, one was an ElCamino and the other was a 70 Vette. The vette was a 4-speed car...ran about 2800 at 72 mph and got about 16 mpg....I always drove a little spirited.
I love a 3.73.


Did you have a 35in tall tire out back or something? My T/A is a 4 speed with 27 diameter tires I swapped to 3.08 and thats 2600-2700 rpm at 70.

#10 Brada

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Posted A week ago

Love the topic. With changes like this, doesn't the speedo cable gear have to be changed? This is a bit of a mystery to me, my '75 had the borg warner swapped for a Muncie years ago before I owned it, and at 60mph on my speedometer I am really going 71-72 mph. My neighbor is a state trooper, so I know for sure,... his gov car is FAST! How or where do we calc what we need for these speedo gear ratio changes when we change components of the drivetrain?

Brad

#11 b_hill_86

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Posted A week ago

Yea, speedometer gears need to be adjusted. There is a drive gear, which is on the transmission output shaft and not easily changed, and there is a driven gear which is what the speedo cable attaches to and is easily changeable.

If you need to increase the speed your speedo reads you need a driven gear with less teeth. 16 or 17 teeth are the fewest if I remember right but it also depends on what drive gear you have. If you need help ironing out what to do to correct it start a thread for that and Ill try to help you the best I can.

#12 Injuneer

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Posted A week ago

Useful info on GM speedo gears:

 

https://www.tciauto....gear-calculator

 

Note that rear tire diameter also affects the speedometer/odometer.


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#13 Brada

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Posted 3 days ago

Thanks guys, will start a new thread. I have tried those calculators previously, that TCI one shows not available.

#14 Injuneer

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Posted 3 days ago

Odd.... TCI works for me.  It's a link I've used many times over the years.

 

Try entering manually (delete space after “www.”)

 

www.  tciauto.com/speedometer-gear-calculator

 

If you mean it shows “gear not available” when you enter the data and hit “calculate” it means there is no appropriate gear available.






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