Ring and pinion gear ratio

[82sbshortbed]

I picked up the truck 2 days ago with new 3.73 posi rear end. On the way home it was running 2700rpm at 55mph. It's a bit more than I figured up before. I got 2700rpm at 65mph but, I was wrong. I figure I'll burn up the motor and transmission driving it long distance at that rpm and speed.

It barks the tires when shifting now and burnouts are readily available whenever I want. Which is cool but, I do want to be able to drive it to work and ****. Lol

So I called quick performance and asked him about it and told him I had 275/60/15's on it. This is what he came up with.

3.08 = 2500rpm at 70mph $100

3.23 = 2500rpm at 65mph $169

3.73 = 2700rpm at 55mph

This calculator was pretty close to those numbers.

https://spicerparts.com/calculators/engine-rpm-calculator

Then I wanted to know what my old ring and pinion gears were. Googled the number and found its most likely a 2.73:1

41 tooth ring gear and 15 tooth pinion gear.

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I thought I could get taller tires and a od transmission to help bring the RPMs down for highway driving but, that's a lot of money and I like my rims and tires.

https://www.hemmings.com/stories/article/th-700-r4-transmissions

So I'm thinking of just replacing the ring and pinion gears to the 3.08 because it's only 100 bucks for the set and 10 bucks for new crush sleeve. Rather than thousands for transmission and tires and rims.

Also need a new radiator with electric fans to keep it cooler. When I pulled in the driveway it was running 220 degrees when I shut it off. That's more than I like. 200 would make me happier than 220. The temp went up to almost 240 after I shut it off too.

So I'd like to hear some opinions about this and if you have something similar, to hear how you like it or don't.

 

[DoubleDingo]

2,700 rpms is nothing. When I had Mean Green and swapped in the 3.54 rear end it ran 2,600 at 70, but the engine loved 3,000, so that is where I ran it most of the time. Never an issue. To run the lower rpms you need to make sure you have the torque to push the slug down the road. I'd leave it at 3.73 if it were me, and get different tires.

 

[DoubleDingo]

I have used this formula on many vehicles to figure out which gear/tire combination to go with.

Corrected the formula here as well, @Goldie Driver pointed out my error.

RPM = MPH x Transmission Gear Ratio x Rear End Gear Ratio x 336/Tire Diameter.

 

[82sbshortbed]

2,700 rpms is nothing. When I had Mean Green and swapped in the 3.54 rear end it ran 2,600 at 70, but the engine loved 3,000, so that is where I ran it most of the time. Never an issue. To run the lower rpms you need to make sure you have the torque to push the slug down the road. I'd leave it at 3.73 if it were me, and get different tires.

Plenty of torque from the 454. Hell, it would break them lose no problem with the 2.73 in it before. I'm afraid it will burn up the motor and transmission driving it long distance at 2700rpm. If not that bbc will empty the tank really fast. Lol

 

[DoubleDingo]

Plenty of torque from the 454. Hell, it would break them lose no problem with the 2.73 in it before. I'm afraid it will burn up the motor and transmission driving it long distance at 2700rpm. If not that bbc will empty the tank really fast. Lol

I misread the original post, I read it as you got a truck, not got your truck. Yeah a bbc has the torque to turn higher gears. I still doubt you would burn up anything turning 2,700, but you would burn more fuel for sure.

 

[Goldie Driver]

I have used this formula on many vehicles to figure out which gear/tire combination to go with.

RPM = Transmission Gear Ratio x Rear End Gear Ratio x 336/Tire Diameter.

I am lost on this one, so I must be doing it wrong.

I assume a TH350C would be a 1:1 final drive.

So :

1 x 3.42 x 336/33 Inch 34.82 RPMS - huh ? If I use 342 as the ratio ,then I get to 3482 RPMs.

 

[DoubleDingo]

I am lost on this one, so I must be doing it wrong.

I assume a TH350C would be a 1:1 final drive.

So :

1 x 3.42 x 336/33 Inch 34.82 RPMS - huh ? If I use 342 as the ratio ,then I get to 3482 RPMs.

Whoops! I left out one critical item...MPH! Thanks for catching that.

Of course this formula doesn't factor in slippage, but I have mainly ran manual transmissions, so slippage wasn't a factor.

Corrected formula is MPH x Transmission Gear Ratio x Rear End Gear Ratio x 336/Tire Diameter.

 

[Goldie Driver]

Whoops! I left out one critical item...MPH! Thanks for catching that.

Of course this formula doesn't factor in slippage, but I have mainly ran manual transmissions, so slippage wasn't a factor.

Corrected formula is MPH x Transmission Gear Ratio x Rear End Gear Ratio x 336/Tire Diameter.

For 70 MPH :


2437 RPMS


I have no tach, so will assume the math works.

 

[RoryH19]

I picked up the truck 2 days ago with new 3.73 posi rear end. On the way home it was running 2700rpm at 55mph. It's a bit more than I figured up before. I got 2700rpm at 65mph but, I was wrong. I figure I'll burn up the motor and transmission driving it long distance at that rpm and speed.

It barks the tires when shifting now and burnouts are readily available whenever I want. Which is cool but, I do want to be able to drive it to work and ****. Lol

So I called quick performance and asked him about it and told him I had 275/60/15's on it. This is what he came up with.

3.08 = 2500rpm at 70mph $100

3.23 = 2500rpm at 65mph $169

3.73 = 2700rpm at 55mph

This calculator was pretty close to those numbers.

https://spicerparts.com/calculators/engine-rpm-calculator

Then I wanted to know what my old ring and pinion gears were. Googled the number and found its most likely a 2.73:1

41 tooth ring gear and 15 tooth pinion gear.

You must be registered for see images attach

I thought I could get taller tires and a od transmission to help bring the RPMs down for highway driving but, that's a lot of money and I like my rims and tires.

https://www.hemmings.com/stories/article/th-700-r4-transmissions

So I'm thinking of just replacing the ring and pinion gears to the 3.08 because it's only 100 bucks for the set and 10 bucks for new crush sleeve. Rather than thousands for transmission and tires and rims.

Also need a new radiator with electric fans to keep it cooler. When I pulled in the driveway it was running 220 degrees when I shut it off. That's more than I like. 200 would make me happier than 220. The temp went up to almost 240 after I shut it off too.

So I'd like to hear some opinions about this and if you have something similar, to hear how you like it or don't.

My 82 and 83 K5's came with 3.08s and 700r4 trans.
My 78 k10 with TH350 also came with 3.08s, seems to be a very common ratio.
These all have small blocks.
I don't think you would notice that much difference if you drop from 3.73 to 3.23.

 

[DoubleDingo]

For 70 MPH :


2437 RPMS


I have no tach, so will assume the math works.

It works. With slippage you can add around 200 rpms.

 

[Goldie Driver]

Sad part is that the 3.42's in 1980 was the upgraded gear set ...




pages (gmheritagecenter.com)

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[Goldie Driver]

It works. With slippage you can add around 200 rpms.

With TCC maybe subtract 100 RPMS ?

So, in theory , real close to the torque peak as rated on paper.

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[DoubleDingo]

With TCC maybe subtract 100 RPMS ?

So, in theory , real close to the torque peak as rated on paper.

You must be registered for see images attach

With lock-up it is direct so the actual number.

 

[Camar068]

I thought I could get taller tires and a od transmission to help bring the RPMs down for highway driving but, that's a lot of money and I like my rims and tires.

Have you ran the calculator with the 700r4 with your current gearing? Having pep thru third would be sweet and still have another gear. Maybe 3.42 and the 700r4 is what your looking for? (if the 700r4 w/3.73).

Also, you should be able to find a complete 3.08 rear end for cheap.....like $120 cheap.

 

[82sbshortbed]

Have you ran the calculator with the 700r4 with your current gearing? Having pep thru third would be sweet and still have another gear. Maybe 3.42 and the 700r4 is what your looking for? (if the 700r4 w/3.73).

Also, you should be able to find a complete 3.08 rear end for cheap.....like $120 cheap.

Yes he said 100 bucks fir set and 10 bucks for the crush sleeve for 3.08. That's why I was thinking cheaper than trans and rims and tires.

I'm gonna drive it some more with new better radiator and see how I like it. It sure gets better traction with that posi and shifts hard. I do like that about it. We'll see, that's why I like hearing different people with different gears give their experience with real time driving.