I have a V6 club cab with the 265/70-16 tires and 3.55 gears.

My speedo is 5 mph slow compared to the GPS on my phone (based on a 9 satelite fix).

My last all highway fuel run was 16.5 MPG over half a tank. The other half of the tank was mixed, and ended up as a 14.5 MPG average (no reset- it went from 16.5 to 14.5 over half a tank). Right now, I've driven 60 miles mixed on this tank, and it's reporting 12.5 MPG.

I've ran 2 bottles of injector cleaner, gone to the V8 TB, and put a new MAP sensor on it with TB change. Air filter is in decent condition. Not sure how long the plugs have been in, but #1 looked fine when I pulled it when I changed TB's.

My math says a 3.65 would put me back to stock equivelent. The nearest i can think of is a 3.73. Is the re-gear worth it, it costs about $800 right?

I think, and the MPG's kinda agree, that my mileage has been lost in the city, having to accelerate from a stop so much.


The MPG figures are from the overhead computer.

 

How much would a Re-gear be, and what would it get me? I know the 8.25 axle is no ford 9", we don't have 400 someodd gear ratios. But I was hoping 3.73 did exist, because I think 3.92 would be too far of a drop, especially in fuel mileage?

I went to Texas A&M and back, it registered 322 miles or something like that, with an average of 16.5. On the way down there (10:30 am to 1:15pm texas time) I got from 18-22 solid instantaneous MPG from the overhead computer, with a 18.6 average. It was fine on flat highway, but kept searching between 3rd and 4th on hills, and even dooped to 2nd a couple times at 50 MPH uphill. It searches the worst at 70MPH, or 65 with a headwind, it will just bounce between 3rd and 4th endlessly until the road flatens out, or I slow down a little. Some of the hills that it downshifted on, weren't all that tall.

Once I got in the stop and go traffic of college station, the instantaneous was in the 10's and 11's. The average when I parked at my friend's apt was 15.7 MPG- a drop of 3 MPG over about 10 miles.

Coming back (9pm-midnight) I got 20-24 MPG, almost no traffic, so i didnt have to modulate speed like i did on the way down. The average when I got home was 17.9 MPG.

Speed readings from GPS, mileage from overhead computer (which doesnt know the 8% speedometer error). Fuel on way down was Quikrip 87 octane, with half a bottle of Lucas Fuel Injector Cleaner. Fuel on way up was H-E-B 87 octane, no cleaner. This was the second dose of cleaner- I ran Lucas Upper Cyl Lubricator for a tank, then ran a tank straight, then I went to A&M with the first half of Injector cleaner, then I'm on a straight tank, and next fill-up, I'll put the other half of the injector cleaner.

I have 265/70-16, 30.6" nominal height, 96.15" nominal circumference. 8% error means a 7.69" circumference difference, so the calibrated nominal is 88.46", or 28.15" nominal diameter (so something like a 235/65-16 or 255/60-16).

So the computer said I went 322 miles, which is actually 348 miles. And 18.6 miles per gallon was actually 20 MPG. 10 MPG was actually 11 MPG. Still, I'm having to think something is up. I'm getting an emissions code (0442 or 0446, i forget), but i couldnt see it as having that big of an effect. I have a 22 gal tank.

 

So i found this link in the FAQ http://www.ringpinion.com/PartsList....+8.25&CatID=10

A caluclator said my equivelent ratio right now is a 3.29, and optimal would be a 3.83. All the gears are the same price $154, what would be better, the 3.90's or the 4.11's?

 

For mileage the lower the better. for acceleration of the line higher is better.

 

right now i'm basically at 3.29, and it's eating gas in the city because I can't get out of the hole. But I'm not sure how low I can go before highway mileage suffers, because most of my driving is city. 3.90/3.92 is the closest i guess, but I'm wondering if 4.10 isn't too low.

Also, any idea what a REPUTABLE shop would charge to do the gear-change? Preferably in the DFW region?

 

you cant have best of both worlds, you either have long gears get better MPG on highway or get short gears and get better MPG city.

If you are using taller tires (1" or more then stock) then getting 3.92s would be your best bet, after the math and bull**** it would make them ~3.73s or around that area.

It will increase your city a tad, but decrease your highway a little.. you have to find a point your happy with both.

Gears are not to expensive, finding a place to install them less then 300$ is the problem, i know a few people that might pick up the job to install them for you, but alot of my hook ups are really busy right now, but i can still ask them.

 

I still have to buy school stuff, so it probably wouldn't be for another few months. I'm just trying to weigh my options, so that when my budget allows, I can just do it and be done (and broke again). With the drag car and all, we just dont have the time/space/equip to do a gear change very quickly. You were the 4.11 club, weren't you User? How much difference is there between 3.92 and 4.11?

FYI, per the GPS on my phone, at 2000 RPM in OD, i'm going 76 MPH. In 3rd, It's 53 MPH.

 

Chrysler uses 4.10s, and i never put them in. Stock 3.92s with a 1in smaller tire puts me around 4.03-4.10 ratio, not much of a difference honestly.

and your mph should not be off by that much, i have the Escort radar that has the GPS sensor on it showing me my speed and its dead on with my speedo, i was tired and didn't read or do the math on the tire sizes you had up there, i just skimmed over the post, but it usually takes a pretty big *** tire to **** up your speedo by 20+ mph, or well very long gears... which is what the large tires do to your gear ratio.

 

For the best balance of performance/fuel economy, you should strive for an effective gear ratio of about 4.10:1. Off the line will be crisp, in-town fuel economy would be up. I have 4.56s, which with my 35" tires, gives me an effective ratio of about 4.11:1. My highway fuel economy is basically unaffected unless I'm up over 75 mph where it's down a bit from before re-gearing. Although the 454rfe transmission has essentially 2 overdrives and helps considerable with highway mileage after re-gearing...

 

Well, you have the Hemi, and i do bet the 2 OD's help. I have the 3.9/42RE combination, with a single .69 overdrive. So I'm way down on power, and the 3-4 shift is killer.

So the 4.11's would be my best option?

Looking at the data I've tabulated below, I still haven't decided between 3.90 or 4.11. My speedometer is off by 7-9%, the speedometer values are in parenthesis (8% average less than actual). I'm thinking 3.90 would be the better to get back to the stock? so I suppose that would be the best option?

stock: 29.05" nominal (window sheet "Sport Plus Group")
gear: 3.55
2K in 3rd: 48.6 mph (48.6)
2K in 4th: 70.4 mph (70.4)

current: 30.60" nominal
gears: 3.55
effective gear: 3.37
2K in 3rd: 53 mph (GPS) (49)
2K in 4th: 76 mph (GPS) (70)

regear to 3.90: 3.70 effective
2K in 3rd: 47.3 mph (43.5)
2K in 4th: 68.5 mph (63)

regear to 4.11: 3.90 effective
2K in 3rd: 44.9 mph (41)
2K in 4th: 65.0 mph (60)

regear to 4.56: 4.33 effective
2K in 3rd: 40.4 mph (37)
2K in 4th: 58.6 mph (54)