I have an 03 ram 1500 3.7 V6 auto trans with a 3.55 gears. Right now it lacks power and enough power to get out of its own way. I'm considering regearing it to 3.92 and adding limited slip, will I gain much going this route? What will my already terrible gas mileage do with the re gear and 285 70 17 tires?

 

From 3.55 to 3.92, I wouldn't even bother. The minimum I would do would be 4.10's. I just went from 3.73's to 4.56's and it is awesome. I would have gone to 4.88's if I could but they don't make a gear that low for my rear end. With a V6 I wouldn't worry too much about bad gas mileage.

 

Ditto on the 4.10s. Your "terrible" gas mileage will likely get worse. That little motor may not like being revved higher.

The 285s might bring the 4.10s back down to 3.XX anyway.

 

At 12.4 mpg regardless of how I drive I can't afford to lose many mpg, the truck spends. 90% of the time so I'm afraid the 4:10s would kill the mpg. I guess I should save the money for regearing and put it towards a hemi.

 

If you put those 285's on, you'll need probably 4.10's just to keep the same effective gear ratio as you had with 3.55's. If you don't like your acceleration now, you won't like it after you do the tires if you don't regear.

 

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What he said.

Probably a good idea. The LSD will run you about $300, I think and the re-gear around a kilobuck. $1,300 will buy a lot of gas (or start the Hemi fund).

 

I found an online calculator for regearing and with the 285s and going with the 4.10s the 70mph rpm was only 2098, that's not near as bad as I was expecting I've been quoted $1200-$1550 to regar to 4.10 and put Detroit lockers in looks like this is actually going to come together and I may be able to hang with the mopeds taking off.

 

I think you are missing it though, while the regear to 4.1 will gain you some acceleration, your larger tires are going to cost you. I figured it out, to get the same effective rear gear ratio with the larger tires you'd need to regear from 3.55 to 3.91, assuming you are running the stock 30" tires. So you will see a slight increase, but I wouldn't say it will be a night and day difference, in fact the extra weight of the tires may suck out whatever extra benefit you are getting, in the end I'd probably call it close to a wash.

I may be misunderstanding though, do you already have the 285's on the truck right now? Or are you thinking of upgrading to 285's when you regear?

Also, do you off-road or drive in snowy/icy conditions often? If not, I would save your money on the LSD, it won't benefit you anything if you only drive on pavement. I don't see anything in your post about that, so if you are just looking to get more acceleration on dry pavement, skip the LSD. When it comes down to open diff/LSD/Locker, it isn't a matter of what is better for everyone, but what is better for your application.

 

I'm sorry I should have made that clear in my first post, I am currently running 285s and the truck is on concrete 95% of the time except when it's deer season then it's on sloppy dirt roads out in pastures etc, the little road going to our property get pretty nasty after a good rain but I've had little problems getting down it before, I only considered LSD because If I was going to spend the money on it I might as well do it right.