Gear ratio help

[61memo]

I have 4.11s on my 66 suburban 6 lug I just found a diff with 3.50 is that going to be better?im running a manual 3 speed will be installing a 400 auto in the future thanks

[derrickmanx1]

If you were going with an overdrive i'd stay where I was. If you want to cruise down the road @ 70 for any length of time the 3.50 would be better. How tall of a tire are you running?

[61memo]

Derrickmanx1 thanks for the reply ill be staying with my three speed manual and 400 turbo in the future, no overdrive 28 inch tall tires.Right now I could only do 50 maybe 55 on the freeway and my motor is screaming I want to cruise all day long at 65 -70 my motor is a 283 v8

[Idaho64GMC]

Originally Posted by 61memo

Derrickmanx1 thanks for the reply ill be staying with my three speed manual and 400 turbo in the future, no overdrive 28 inch tall tires.Right now I could only do 50 maybe 55 on the freeway and my motor is screaming I want to cruise all day long at 65 -70 my motor is a 283 v8

You'll be much happier at the 65-70 range with the 3.50, should drop your RPM's considerably

[Captainfab]

What type of differential did you find that has 3.50 gears? The closest thing in a truck 12 bolt is 3.42 gears. If it's a Dana 44 then it would be 3.54 gears. Either one of those would be good for highway cruising with a 283 since they don't mind the rpm's, which is where they make their power. The 3.07 gears would drop the rpm's for a more comfortable highway cruise, but I think the little 283 may struggle with that. That TH400 is sucking a lot of power from that 283. Too bad you didn't have a TH350.

[derrickmanx1]

Originally Posted by Captainfab

What type of differential did you find that has 3.50 gears? The closest thing in a truck 12 bolt is 3.42 gears. If it's a Dana 44 then it would be 3.54 gears. Either one of those would be good for highway cruising with a 283 since they don't mind the rpm's, which is where they make their power. The 3.07 gears would drop the rpm's for a more comfortable highway cruise, but I think the little 283 may struggle with that. That TH400 is sucking a lot of power from that 283. Too bad you didn't have a TH350.

x2 I think with your setup you are looking at w/4.11 you are at about 3600-3700 rpm @ 70. w/3.42's you'd be around 3000-3100 @70 w/3.07's you'd be around 2700 rpm. The 3.07's would be the cruisers choice. I think you'd be happier with a turbo 350 or 700r4 both have a lower first gear. I had a 302 sbc with both started with the 350 and went to the 400 and it definately changed the way it ran. You'll lose about 10-15hp but the 400 is stronger for sure. If you are changing transmissions anyway i'd go with the 700r4 you get a 3.06 first gear and a .7 overdrive. With 3.42's that means it takes off slightly better than your 400 w 4.11's and cruises about 2000 rpm @ 70. Hope this helps.

[kieth]

Originally Posted by 61memo

I have 4.11s on my 66 suburban 6 lug I just found a diff with 3.50 is that going to be better?im running a manual 3 speed will be installing a 400 auto in the future thanks

You would be much happier with a 700r4 rather than the 400, send me the following information and I will e mail you a sheet that shows how your truck performs now and how it will perform after the change.

1. engine
2. transmission (3 speed) ratio 1:1 400 auto ratio 1:1 you need a OD
3. rear axle ratio
4. rear tire diameter from ground to top of the tire....

pm me here on the board with your email and I will send it to you. If you are going to be making other changes (engine etc let me know)