Ring and pinion gear ratio

82sbshortbed

Fuckemall!!
Joined
Mar 1, 2018
Posts
9,504
Reaction score
28,692
Location
SE Texas
First Name
Doug
Truck Year
1982
Truck Model
1500
Engine Size
454
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.
 

DoubleDingo

Full Access Member
Joined
Jul 3, 2012
Posts
7,291
Reaction score
7,156
Location
Right where I am
First Name
Bagoomba
Truck Year
1981, 1965
Truck Model
81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
Engine Size
Carb'ed Vortec 350; 1972 L48 350
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

Full Access Member
Joined
Jul 3, 2012
Posts
7,291
Reaction score
7,156
Location
Right where I am
First Name
Bagoomba
Truck Year
1981, 1965
Truck Model
81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
Engine Size
Carb'ed Vortec 350; 1972 L48 350
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.
 
Last edited:

82sbshortbed

Fuckemall!!
Joined
Mar 1, 2018
Posts
9,504
Reaction score
28,692
Location
SE Texas
First Name
Doug
Truck Year
1982
Truck Model
1500
Engine Size
454
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

Full Access Member
Joined
Jul 3, 2012
Posts
7,291
Reaction score
7,156
Location
Right where I am
First Name
Bagoomba
Truck Year
1981, 1965
Truck Model
81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
Engine Size
Carb'ed Vortec 350; 1972 L48 350
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

Full Access Member
Joined
Mar 19, 2018
Posts
3,221
Reaction score
4,630
Location
Houston, Texas
First Name
Britt
Truck Year
1980
Truck Model
GMC K1500 Suburban
Engine Size
350
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.


:think:
 

DoubleDingo

Full Access Member
Joined
Jul 3, 2012
Posts
7,291
Reaction score
7,156
Location
Right where I am
First Name
Bagoomba
Truck Year
1981, 1965
Truck Model
81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
Engine Size
Carb'ed Vortec 350; 1972 L48 350
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.


:think:

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

Full Access Member
Joined
Mar 19, 2018
Posts
3,221
Reaction score
4,630
Location
Houston, Texas
First Name
Britt
Truck Year
1980
Truck Model
GMC K1500 Suburban
Engine Size
350
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. :anitoof:
 

RoryH19

Full Access Member
Joined
Aug 21, 2015
Posts
1,538
Reaction score
949
Location
Texas
First Name
Rory
Truck Year
1987
Truck Model
R10 Silverado SWB
Engine Size
350 TBI
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

Full Access Member
Joined
Jul 3, 2012
Posts
7,291
Reaction score
7,156
Location
Right where I am
First Name
Bagoomba
Truck Year
1981, 1965
Truck Model
81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
Engine Size
Carb'ed Vortec 350; 1972 L48 350

DoubleDingo

Full Access Member
Joined
Jul 3, 2012
Posts
7,291
Reaction score
7,156
Location
Right where I am
First Name
Bagoomba
Truck Year
1981, 1965
Truck Model
81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
Engine Size
Carb'ed Vortec 350; 1972 L48 350
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

Supporting Member
Supporting Member
Joined
Feb 5, 2014
Posts
3,047
Reaction score
1,315
Location
Kentucky
First Name
David
Truck Year
1986
Truck Model
K10/LM7 5.3/4L60e/np208/3.73/32"
Engine Size
10 yrs Air Force
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

Fuckemall!!
Joined
Mar 1, 2018
Posts
9,504
Reaction score
28,692
Location
SE Texas
First Name
Doug
Truck Year
1982
Truck Model
1500
Engine Size
454
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.
 
Last edited:

Forum statistics

Threads
34,127
Posts
709,779
Members
22,191
Latest member
jaziclan
Top