3.73s with 35s 72 K10 Th350 Auto & stock 350?

[cadillac_al]

My 76 K10 350/th350/30"tires tows 6000 lb trailers with 3.08 gears and I don't need to downshift for hills. I wouldn't worry about the downshifting aspect.

[fishmunger]

Currently the truck has 4.56s, and it's in 3rd gear at about 15 mph going down the road! Takes 3000 rpms to go 65, even at 2500 its barely pulling 55 and I'm practically getting run off the highway...

[fishmunger]

cadillac al - Are you satisfied with your setup for towing? How is your off the line response? Your effective ratio is pretty similar, actually slightly higher, than what I would be looking at with 3.73s

[4u2nv]

Originally Posted by fishmunger

Currently the truck has 4.56s, and it's in 3rd gear at about 15 mph going down the road! Takes 3000 rpms to go 65, even at 2500 its barely pulling 55 and I'm practically getting run off the highway...

That's the rpm I'm getting at the same speed with 4.11's and 35's , It's off the line like a rapped ape and through 2nd in a flash , I shouldn't think that there is any thing to worry about for towing except your gas mileage.

[57taskforce]

Originally Posted by 4u2nv

That's the rpm I'm getting at the same speed with 4.11's and 35's , It's off the line like a rapped ape and through 2nd in a flash , I shouldn't think that there is any thing to worry about for towing except your gas mileage.

Are you sure your rpms are the same? Mine has 4:11’s, Sm465 with 1:1 4th gear, and 31.5”ish tires on it and it doesn’t quite pull 3K@65. With 4:11’s and 35’s
You should be closer to 2500@65, and 2100@55. That’s of course assuming a 1:1 transmission high gear.

[fishmunger]

Thank you for all the responses!

Mike C - I'm curious, did your kid's rig see any towing?

[Mike C]

Originally Posted by fishmunger

Thank you for all the responses!

Mike C - I'm curious, did your kid's rig see any towing?

It has not seen any towing, but I don't see any reason it wouldn't do well at it.

[4u2nv]

Originally Posted by 57taskforce

Are you sure your rpms are the same? Mine has 4:11’s, Sm465 with 1:1 4th gear, and 31.5”ish tires on it and it doesn’t quite pull 3K@65. With 4:11’s and 35’s
You should be closer to 2500@65, and 2100@55. That’s of course assuming a 1:1 transmission high gear.

350 turbo tranny

[1976gmc20]

Originally Posted by cadillac_al

My 76 K10 350/th350/30"tires tows 6000 lb trailers with 3.08 gears and I don't need to downshift for hills. I wouldn't worry about the downshifting aspect.

Must not be very steep hills. My old 350/350 K trucks wouldn't even climb the hills in Colorado in high gear when empty

And one I bought brand new. The other was in the family since new and I got it at about 12 years old, maybe 65K miles.

Maybe altitude makes a difference ???

[Mike C]

3.73 and 35" tires are a great choice with a TH350. Same setup we did in my kids Jimmy. And if you had a manual trans you'd probably like the 4.56.

Based on your description of use, I'd go with the 3.73. On my kids truck we also did a 204/214 cam with an Edelbrock intake and dual exhaust on 2.5" rams horns so a little more power than stock.

Converter slippage is a factor making 3.73 and a TH350 almost same highway rpm as an sm465 and 4.10 which is my favorite road combo.