Help with gear size please

[Tablesaw818]

Hey all! I have a 78 K10 with 35” tires on it. I recently swapped out the sm465 for an NV4500. It has a Blue Print 383 so it’s got power. My problem is that 5th gear is too tall to use without keeping my foot mashed to the floor. I would really like some input on what gear ratio I should swap the 3.73 in the axles with. Thanks in advance.

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[nvrenuf]

I’d go with at least 4.56. If it were mine I’d run 4.88 or 5.13.

 

[xm20k]

I’d go with at least 4.56. If it were mine I’d run 4.88 or 5.13.

Same

My 388/powerglide is running a 4.56 with a 28" rear tire, If I was running overdrive and a taller tire, I'd say 4.88 minimum 5.13 would probably be better depending on the final drive of the trans.

 

[bucket]

I agree with these fellas ^^^

 

[Ricko1966]

Does it have enough power for everything you're doing in 1st? Going to a taller ratio is just going to move all the gears lower. So unless you need more 1st gear it might be in your best interest to drive it as a 4 speed.

 

[xm20k]

Does it have enough power for everything you're doing in 1st? Going to a taller ratio is just going to move all the gears lower. So unless you need more 1st gear it might be in your best interest to drive it as a 4 speed.

Ya too low of a rear gear could make first unusable depending on what first gear is, my M715 had a 6.32 first and with its 5.88 rear gears first was unusable for street use so it basically became a 3 speed. 55mph wide open downhill with a tail wind while spinning 5000rpm is not fun for very long.

 

[bucket]

Does it have enough power for everything you're doing in 1st? Going to a taller ratio is just going to move all the gears lower. So unless you need more 1st gear it might be in your best interest to drive it as a 4 speed.

You mean shorter/steeper ratio? Higher numerically.

4.10's and 35's is rather long legged. Imho, the ONLY reason to run that combo would be for highway efficiency if there's no overdrive. But there is overdrive here...

 

[Ricko1966]

You mean shorter/steeper ratio? Higher numerically.

4.10's and 35's is rather long legged. Imho, the ONLY reason to run that combo would be for highway efficiency if there's no overdrive. But there is overdrive here...

I figured if he couldn't pull 5th gear and his original goal was to lower highway rpm ,if he changes ratios to pull 5th its going to have similiar highway rpm as if he just drives it in 4th,and might make 1st gear useless. Yes lower gears, higher numerically.
As an example the 5.13s mentioned above with a 700r4 ( example only) would be a final drive ratio of 3.74 he'd be turning the same rpm as a non overdrive transmission with 3.73s no gain on the highway but more 1st gear.

 

[Rustisbest]

Same transmission and tire size as my Tahoe. With 4.88 gears it runs right around 2500 at 70 mph in overdrive.

5.61 or 6.something low gear is good for pulling out from steep hills to save the clutch, pulling a trailer or slow speeds offroad.

 

[bucket]

I figured if he couldn't pull 5th gear and his original goal was to lower highway rpm ,if he changes ratios to pull 5th its going to have similiar highway rpm as if he just drives it in 4th,and might make 1st gear useless. Yes lower gears, higher numerically.
As an example the 5.13s mentioned above with a 700r4 ( example only) would be a final drive ratio of 3.74 he'd be turning the same rpm as a non overdrive transmission with 3.73s no gain on the highway but more 1st gear.

3.73's, 35's and no overdrive is good on the interstate, but sucks at lower speeds. Your math backs up my thoughts that 5.13 would be great.

 

[Ricko1966]

3.73's, 35's and no overdrive is good on the interstate, but sucks at lower speeds. Your math backs up my thoughts that 5.13 would be great.

But he is going to be turning the same rpm as if he left it in 4th with his 3.73s so he loses the advantage of overdrive and gains a ton in 1st gear.

 

[bucket]

But he is going to be turning the same rpm as if he left it in 4th with his 3.73s so he loses the advantage of overdrive and gains a ton in 1st gear.

Yep. Exactly. He didn't need overdrive with that combo. But now with an overdrive gear, he can regear for more power and efficiency and retain the low (but not too low) highway rpm's he had before.

This is coming from someone that runs 4.56's and 5.13's with 36's. It's not at all too much gear for lower speeds.

I've also run 35's and 36's with 3.73 and no overdrive. It's less than ideal at low speeds, but great on the interstate.

 

[bucket]

Keep in mind that most 00's GM 2500 trucks are known for their power and efficiency compared to our older trucks. They ran 3.73 and 4.10 gears with 32" tires.

 

[Ricko1966]

Yep. Exactly. He didn't need overdrive with that combo. But now with an overdrive gear, he can regear for more power and efficiency and retain the low (but not too low) highway rpm's he had before.

This is coming from someone that runs 4.56's and 5.13's with 36's. It's not at all too much gear for lower speeds.

I've also run 35's and 36's with 3.73 and no overdrive. It's less than ideal at low speeds, but great on the interstate.

I laughed but didn't want to post a laugh emoji to be misunderstood. I laughed at the change gears,end up with the same final drive,he didn't need overdrive comment.