3.08 Gears. What to Swap to?

[Normmus]

Truck is a 1977 K10 with a stock 350, SM465, 31 inch tires, and 3.08 gears. It sees about 70% highway, 20% in town driving, and 10% low speed yard driving (some deep snow, small hills). No towing at all. I am satisfied with the highway performance, but it feels like it needs deeper gears around town but I can live with it. I want to go up to a 33 inch tire and lift it a bit. I know I will need to regear to be satisfied but for new gears I am having a hard time deciding between 3.73 and 4.11. Wondering if anyone has the same drivetrain as my truck and done a swap to 3.73 or 4.11 and what you liked/didn't like about it.

Edited to add - I do not want to swap a different transmission in.

 

[Ricko1966]

Truck is a 1977 K10 with a stock 350, SM465, 31 inch tires, and 3.08 gears. It sees about 70% highway, 20% in town driving, and 10% low speed yard driving (some deep snow, small hills). No towing at all. I am satisfied with the highway performance, but it feels like it needs deeper gears around town but I can live with it. I want to go up to a 33 inch tire and lift it a bit. I know I will need to regear to be satisfied but for new gears I am having a hard time deciding between 3.73 and 4.11. Wondering if anyone has the same drivetrain as my truck and done a swap to 3.73 or 4.11 and what you liked/didn't like about it.

Edited to add - I do not want to swap a different transmission in.

Get a tach,drive your truck,note your rpms at different speeds. Then look at an online gear ratio calculator,see how many rpms you will be turning at the speeds you commonly drive at. Go drive your truck at those rpms. Are you comfortable at those rpms? Problem solved.

 

[Shorty81]

My truck is a 86 K20. 496bb, 465, 208, 31" tires, 3 :73. That setup is perfect for me. I'm 2000 rpm at 55.

 

[Redfish]

My '87 has the stock TBI 350, SM465, 3:42 gears and 33 inch tires. My motor has a few more horsepower than yours so this isn't apples to apples...

I don't have a tach so I cannot give specifics here but for all around town, backroads, 55 mph two lane highways, my gearing is okay. It still pulls like a tractor in 4 Low and as you know the "L" gear on that SM465 is pretty low. I use this pretty frequently. I have not wished for anything lower or higher, but this truck is not my daily driver either.

Based on your usage I would say 3:73. I think 4:11s on the highway would be annoying with 33 inch tires.

My Truck:

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[legopnuematic]

3.42-3.73 I think would be satisfactory for your usage.

With the 6.55:1 first (or low) of the sm465 and if that’s not enough you have low range with the transfer case to get something moving.

 

[Snoots]

I've got 3.73 but wish I had 3.42. Kinda $$$$ when you have 4WD.

 

[Normmus]

Thanks to all for the answers. I'll be looking at 3.73

 

[newguy11]

If any of you guys want I built rear gear / rpm calculator on Microsoft excel.
Send me a private message with your email and I’ll send it to you.

It’s set up to compare different rear gears combos with either the TH350 or 700r4.
You could add different trans if you had the inclination

 

[MikeB]

Only you know what kind of engine speeds you can live with on the highway. Compare your current 3.08 with 31" tires, to a 3.73 and 4.11 with 33" tires.

Calculate RPM for Given Speed(MPH), Rear Gear Ratio, and Trans Gear Ratio

Calculate RPM for Given Speed(MPH), Rear Gear Ratio, and Trans Gear Ratio

purperformance.com

 

[straydog371]

Truck is a 1977 K10 with a stock 350, SM465, 31 inch tires, and 3.08 gears. It sees about 70% highway, 20% in town driving, and 10% low speed yard driving (some deep snow, small hills). No towing at all. I am satisfied with the highway performance, but it feels like it needs deeper gears around town but I can live with it. I want to go up to a 33 inch tire and lift it a bit. I know I will need to regear to be satisfied but for new gears I am having a hard time deciding between 3.73 and 4.11. Wondering if anyone has the same drivetrain as my truck and done a swap to 3.73 or 4.11 and what you liked/didn't like about it.

Edited to add - I do not want to swap a different transmission in.

My drivetrain is pretty much the same as yours: 1978 K10 with the original SBC 350, SM465, 32 inch tires, and 3.08 gears. I installed a tach last winter...at 60 mph I'm seeing 1950 RPM.
I just used the calculator that Mike B linked above. and it shows 1940 RPM with my setup...close enough to verify my tach is pretty accurate.
I'll also be re-gearing and was "undecided" until this conversation was started. 3.73 ratio sounds like the winner for me too...60mph / 2349 RPM. I can live with that.
Plan to rebuild both axles over the winter...I'll definitely be asking questions and posting pictures along the way.