Rear end question

[Bradydz]

I feel my rear end gears are just too low for how I drive my truck. (daily driver). I've got really great acceleration, but not too great of a top speed, around 80 in high RPM (no tach, low gears I'm sure, somewhere around 4.56. it's not the stock rear end, but I was not the one that put it in). What gear ratio would be best for me, with the stock 4-speed and a 355 SBC engine? I still want somewhat good acceleration, but a better top speed.

[kenbob87]

3.73's are always a pretty good all around gears in my opinion

[Brad54]

I've got 3.42 gears in mine, with a 4spd manual overdrive.
3rd is 1:1, 4th is .72:1.
Good acceleration off the line, and decent RPM/MPH in 3rd... (honks down the highway at 75/80 all day long).

-Brad

[donthekawguy]

My truck is the same way. I have a tach but no speedo but I had my kid follow me home when I got the truck. I was doing 45 mph at 2900 rpm. I got a taller set of tires put on the back and now I can cruise at around 55 at 3000 rpm. If I get motivated enough this week I'm going to pull the cover off the diff and count the teeth to find out what gears I have. I'm guessing around 4.72 or so. When we were kids my friend had a 69 camaro that had 5.11's in a 9 inch with a 12.5 compression 327. The motor had a pete jackson gear drive and you could hear that thing from miles away. It would top out in town around 30-35 mph. But out at the track it would run mid 11's. Not bad for small block.

[Captainfab]

Is your truck a C10 or a C20?. If it's a C20, you will be better off changing the entire rear end, if you have the Eaton HO52.

If you have a C10, you likely have a 12 bolt. The 3.42 gear is a good comprimise between decent acceleration and not too bad of rpm's on the highway. In my Suburban with the 3.42's and 275/60-15 tires, I am turning about 3100 @ 70 mph. I have heard of guys running the 3.07 gears with a 4 speed, but I don't know what the acceleration is like.

[Bradydz]

Originally Posted by kenbob87

3.73's are always a pretty good all around gears in my opinion

How's the acceleration?

Originally Posted by Brad54

I've got 3.42 gears in mine, with a 4spd manual overdrive.
3rd is 1:1, 4th is .72:1.
Good acceleration off the line, and decent RPM/MPH in 3rd... (honks down the highway at 75/80 all day long).

-Brad

3.42 is what I had in mind.. Thank you for the info about highway, too.

Originally Posted by donthekawguy

My truck is the same way. I have a tach but no speedo but I had my kid follow me home when I got the truck. I was doing 45 mph at 2900 rpm. I got a taller set of tires put on the back and now I can cruise at around 55 at 3000 rpm. If I get motivated enough this week I'm going to pull the cover off the diff and count the teeth to find out what gears I have. I'm guessing around 4.72 or so. When we were kids my friend had a 69 camaro that had 5.11's in a 9 inch with a 12.5 compression 327. The motor had a pete jackson gear drive and you could hear that thing from miles away. It would top out in town around 30-35 mph. But out at the track it would run mid 11's. Not bad for small block.

5.11?! No go there, man. Let me know what you've got, pretty curious.
How do you not have a speedo? Or is it just warn out?

Originally Posted by Captainfab

Is your truck a C10 or a C20?. If it's a C20, you will be better off changing the entire rear end, if you have the Eaton HO52.

If you have a C10, you likely have a 12 bolt. The 3.42 gear is a good comprimise between decent acceleration and not too bad of rpm's on the highway. In my Suburban with the 3.42's and 275/60-15 tires, I am turning about 3100 @ 70 mph. I have heard of guys running the 3.07 gears with a 4 speed, but I don't know what the acceleration is like.

GMC i1000, not sure if that'd change what would be under there. 3.42 does sound like a good one for me, and I'm running 235's.

[donthekawguy]

5.11?! No go there, man. Let me know what you've got, pretty curious.
How do you not have a speedo? Or is it just warn out?

I think the cable is broken just need to get the old one out so I make sure i get the correct length. Yeah the 5.11's made a cruise around town a horrible time. Mine is ok once I get into town but the 7 miles I have to drive suck.

[luvbowties]

Originally Posted by donthekawguy

My truck is the same way. I have a tach but no speedo but I had my kid follow me home when I got the truck. I was doing 45 mph at 2900 rpm. I got a taller set of tires put on the back and now I can cruise at around 55 at 3000 rpm. If I get motivated enough this week I'm going to pull the cover off the diff and count the teeth to find out what gears I have. I'm guessing around 4.72 or so. When we were kids my friend had a 69 camaro that had 5.11's in a 9 inch with a 12.5 compression 327. The motor had a pete jackson gear drive and you could hear that thing from miles away. It would top out in town around 30-35 mph. But out at the track it would run mid 11's. Not bad for small block.

Hi, donthekawguy. Just may save a bit of time: No need to remove cover/count teeth to det. ratio. Just jack up one wheel(if non-posi), rotate tire one rev, count total turns of driveshaft PLUS add the proportion of final, partial turn to get ratio. Ex: If total turns is 3 plus a partial, it is a 3.XX:1. If total turns is 4 plus a partial, it is a 4.xx:1.

To determine the "xx" part: measure the inches of the circumference (of d'shaft) used up by the partial turn, and divide it by the circumference of driveshaft. If shaft is 9.42" in circumference(meaning shaft is 3" in diameter), and partial revolution took up 5.2 inches, then 5.2 divided by 9.42 is .552. Round .552 to closest known available ratios, and get .55. Thus, 3 total plus .55 partial gives 3.55:1 gear ratio.

To get accurate msmt. of a partial turn, put a piece of masking tape around circumference of d'shaft and measure along it to det. inches the partial turn 'used up'.

HTH

[donthekawguy]

I just barfed trying to read how to figure out gear ratio's. lol It's a posi.

[luvbowties]

Originally Posted by donthekawguy

I just barfed trying to read how to figure out gear ratio's. lol It's a posi.

If you wanna barf some more, and you have a posi: Get both wheels up do same as in non-posi--exc. whatever you get is neither doubled nor halved--just ONE rotation.

Seriously, tho', a 4.56:1 diff'l ratio simply means it takes 4.56 rotations of d'shaft to make rear wheels turn once!

[luvbowties]

Originally Posted by donthekawguy

I just barfed trying to read how to figure out gear ratio's. lol It's a posi.

Final info: Here is a much simpler explanation. It, btw, corrects error I made in my 1st replies--where I got posi and non-posi reversed--on non-posi you need to rotate tire TWO turns due to going thru spider gears. Enjoy:

>> http://www.ehow.com/how_12156231_cal...ear-wheel.html <<