Gear ratio advice 14 bolt BBC

[Marc Rexroad]

79 cab and chassis currently with stock 350. Runs well but am finishing up a 454 build that will in this fall.

14 bolt 10.5" rear is currently 4.10 gears and am tempted to change to a higher ratio. 3.7, 3.5? or even the 3.21. Just trying to keep the engine happy an lower rpm a bit.

The mechanics of the swap are not a problem I am just hoping for some guidance. I will stick with the stock 4 speed with the granny low 1st.

Thanks in advance folks!

 

[82sbshortbed]

I'm not any help. I'm putting in 3.73 posi in my c10 short bed with 454 bbc.

 

[Bextreme04]

Tire size and what your daily usage will look like are going to be your biggest determining factors. I'm keeping the 4.10's in mine, but I run 35's and will be swapping in a 4L80e when I do the swap from 350 to 454.

Because you have the 465, you can get away with a pretty tall gear in the rear and still have plenty of pulling power, especially with the 454. I'd go with no taller than 3.73.

Using a gear ratio calculator could help as well. Using the spicer one, a 31" tall tire and 4.10's gets you 3100rpm at 70mph. Going to a 3.73 only drops that to 2900RPM. 3.21's drops it to 2500rpm. Alternatively, 3.73's and a NV4500(5sp w/OD) would have you at 2000rpm in OD with a 31" tire.

My combo of 454/4L80e with 4.10's and 35" tires gets me 1950rpm at 70MPH in OD.

Here's the calculator: https://spicerparts.com/calculators/engine-rpm-calculator

 

[DoubleDingo]

79 cab and chassis currently with stock 350. Runs well but am finishing up a 454 build that will in this fall.

14 bolt 10.5" rear is currently 4.10 gears and am tempted to change to a higher ratio. 3.7, 3.5? or even the 3.21. Just trying to keep the engine happy an lower rpm a bit.

The mechanics of the swap are not a problem I am just hoping for some guidance. I will stick with the stock 4 speed with the granny low 1st.

Thanks in advance folks!

3.54 is a great gear. The 68-72 C20 Suburbans came with those gears. They had 396/TH400/3.54 Dana 60. I have one of those 3.54 D60's and it made my truck run way better on the road. 70 mph is roughly 2,600 rpms. That 454 will be able to push a taller gear like 3.42 no problem.

 

[Craig 85]

My current K30 has 3.73s. My last truck had 4.10s. Both had 32.8" tall 33's and automatics. The 3.73 is running around 2500 RPM at 65 MPH and the 4.10 was closer to 3000 RPM.

It depends on your use. If you are running a stock size tires 30-31 inches with the manual you may be okay with a 3.73 since the driveline will be locked. If you don't plan on hauling or towing the 3.21 would be nice to keep the RPMs down.

 

[Marc Rexroad]

Thanks for the responses folks. More info....

Tires are 31" tall and will be used as a daily driver and jobsite truck carrying supplies. Not much towing to be done.

 

[Camar068]

any hills do 3.90 or 4.10. I've got lots of hills and regret going 3.73 instead of 4.10

 

[cstew47]

79 cab and chassis currently with stock 350. Runs well but am finishing up a 454 build that will in this fall.

14 bolt 10.5" rear is currently 4.10 gears and am tempted to change to a higher ratio. 3.7, 3.5? or even the 3.21. Just trying to keep the engine happy an lower rpm a bit.

The mechanics of the swap are not a problem I am just hoping for some guidance. I will stick with the stock 4 speed with the granny low 1st.

Thanks in advance folks!

Missing a few info points. What is your tire size and tranny fourth gear ratio?

 

[nvrenuf]

Doesn’t the 14ff ratio selection go 4.10, 3.73, 3.21? I wasn’t aware the was any option between 3.73 and 3.21.

 

[Bextreme04]

Doesn’t the 14ff ratio selection go 4.10, 3.73, 3.21? I wasn’t aware the was any option between 3.73 and 3.21.

USA Standard gear offers a 3.73, 3.42, and 3.21 for a 14BFF. They would all need a 4.10 or lower carrier.

 

[73c20jim]

I have a 350 CID stock (basically) with TH350 and 3.73's in my 14B.

Works well for me.

 

[nvrenuf]

USA Standard gear offers a 3.73, 3.42, and 3.21 for a 14BFF. They would all need a 4.10 or lower carrier.

Cool. I always thought the 3.42 listing was people confusing ratios available for the semi floater.