Used 489

[LinceCuda]

Picked up a 489 chunk this past weekend for $100 and $20 for gas to go get it. I'll be going with 3.55 gear ratio after reading several posts and replies, seems to be a good all around ratio. It's a open unit so I will need to buy a sure grip posi unit. This wii replace my original but broken 741 unit.

[Cuda Cody]

Sure Grip w/ 3.55 in a 489 is a good set up.   

[dodj]

Lots of people seem to like them but never thought the 3.55's were any good at all. Not particularly good off the line and not a good highway gear. IMO, does nothing well.

[Chryco Psycho]

I always used 3.23 but then there is a lot of open space in western Canada & often a lot of distance between towns so Highway was more important . but I also used the OD trans a lot too which give a better ratio off the line .
3.55 is a good mid range gear

[303 Mopar]

I have 3.55's in my Cuda and had them in my '71 Challenger with 408 stroker. This was the perfect gear IMO.  Jump off the line yet nice cruising gear.  I have 3.23's in the Charger but it has 505 stroker so it gets up of the line anyways. 

[Shane Kelley]

Gear ratio is subjective and dependent on so many different levels. What do you want from your car? Low end, top speed or something in the middle. Engine torque and tire diameter are big factors. I find the big torque motors like a little taller gear like 3.23 or 3.55. Gives the motor something to lean on so to speak. The smaller motors can make good hp numbers but don't produce the torque. So rpm is needed to compensate. Hence the lower gears. If you don't run your car hard and just enjoy driving it. Go with a 3.23.

So I changed from a 3.91 to a 3.55 because I thought I wanted a little taller gear for getting out on the road and cruising. I figured that small of a change really wouldn't make much difference in performance. Did some test runs and thought the car pretty much ran the same. Nothing extensive. But after some more seat time and testing with real data. Not just seat of the pants feel.  I have decided that my little 340 likes the 3.91 better. It has to work to pull the rpm's up and takes longer. I liked the way it would almost instantly pull 6400 and grab another gear. Now I'm watching the tach pull to that gear and then shifting. Yes it really turns some rpm out on the highway with 3.91 compared to 3.55 but I have decided it's a sacrifice I can live with. So I'm going back to the 3.91's. Remember everyone's likes and combinations are different. These are what my combo is producing. These are averages of 6 runs per gear set.
Here's the numbers. These numbers are with some pretty good tire spin out of the hole.  If I backed off the throttle and let it hook it killed 0-60 and ET. Motor wants to stay up in the rpm range.
3.55       0-60mph  6.4 sec          0-100 14.36           1/4 mile ET 13.68      1/4 mile speed   93mph
3.91       0-60mph  5.4 sec          0-100 13.72           1/4 mile ET 12.97      1/4 mile speed   97mph   

[LinceCuda]

Gear ratio is subjective and dependent on so many different levels. What do you want from your car? Low end, top speed or something in the middle. Engine torque and tire diameter are big factors. I find the big torque motors like a little taller gear like 3.23 or 3.55. Gives the motor something to lean on so to speak. The smaller motors can make good hp numbers but don't produce the torque. So rpm is needed to compensate. Hence the lower gears. If you don't run your car hard and just enjoy driving it. Go with a 3.23.

So I changed from a 3.91 to a 3.55 because I thought I wanted a little taller gear for getting out on the road and cruising. I figured that small of a change really wouldn't make much difference in performance. Did some test runs and thought the car pretty much ran the same. Nothing extensive. But after some more seat time and testing with real data. Not just seat of the pants feel.  I have decided that my little 340 likes the 3.91 better. It has to work to pull the rpm's up and takes longer. I liked the way it would almost instantly pull 6400 and grab another gear. Now I'm watching the tach pull to that gear and then shifting. Yes it really turns some rpm out on the highway with 3.91 compared to 3.55 but I have decided it's a sacrifice I can live with. So I'm going back to the 3.91's. Remember everyone's likes and combinations are different. These are what my combo is producing. These are averages of 6 runs per gear set.
Here's the numbers. These numbers are with some pretty good tire spin out of the hole.  If I backed off the throttle and let it hook it killed 0-60 and ET. Motor wants to stay up in the rpm range.
3.55       0-60mph  6.4 sec          0-100 14.36           1/4 mile ET 13.68      1/4 mile speed   93mph
3.91       0-60mph  5.4 sec          0-100 13.72           1/4 mile ET 12.97      1/4 mile speed   97mph   

I have 3.55's in my Cuda and had them in my '71 Challenger with 408 stroker. This was the perfect gear IMO.  Jump off the line yet nice cruising gear.  I have 3.23's in the Charger but it has 505 stroker so it gets up of the line anyways. 

I always used 3.23 but then there is a lot of open space in western Canada & often a lot of distance between towns so Highway was more important . but I also used the OD trans a lot too which give a better ratio off the line .
3.55 is a good mid range gear

Lots of people seem to like them but never thought the 3.55's were any good at all. Not particularly good off the line and not a good highway gear. IMO, does nothing well.

Sure Grip w/ 3.55 in a 489 is a good set up.   

Great replies and info guys and thanks for posting those numbers Shane. The other ratio I was kicking around was the 3.91, I would be interested in knowing what rpm you were at on the highway with the 3.91 Shane? Thanks everyone for chiming in.

[Shane Kelley]

25" tall tire. 4000rpm @ 75mph    3.55 is 3500 rpm @ 75mph

[LinceCuda]

25" tall tire. 4000rpm @ 75mph    3.55 is 3500 rpm @ 75mph

Thanks Shane, and now something else for me to think about