I have the stock 3.08 gears in my i6 and was wondering if i would get better gas mileage if i put in higher gears. How much would it infect my acceleration? And what gear ratio would be the best for improving MPG.

 

If you get 3:73's or 3:55's or 4:10's or what not, it will give you better aceleration, and tow more easily, but you will turn higher RPMs on the highway. I'd imagine the 3:08s are good for gas mileage.

 

It also depends on your transmission, tires and what type of driving you do.

Around town, where you are shifting through the gears all the time, the gear ratio that keeps you in the powerband the most is what would work best.

On the highway, once you get the "mass" rolling, it does not take much power to maintain the speed (barring steep hills/heavy loads) so a numerically lower gear ratio will normally get you better MPG.

Mine has the 3.08, 235/15 tires and e4od trans and generally I get 17-20 on the highway.

Around town though I get 12 because is has little acceleration due to the high gears and I generally have to get into it a little more to stay with traffic.

Just some thoughs

Jim

 

This is funny I have 4.10 gears in mine and am thinking about installing 3.08 or 2.73 so I can get better milage on the interstate. for me to get any kind of milage I have to maintain 50-55. I would say it all depends on what kind of driving you are going to be doing. I thought about adding an overdrive so I can select when higher gears when i want them.

 

I think 3.08's are the best all around gear ratio unless you do a lot of towing. I thought about switching to a different gear when I rebuilt the rear end, but there really wasn't anything I do with the truck that could have been done noticably better with a different gear.

 

Just wanted to ask what kind of mileage I should expect if the rpms are at about 2100-2200 rpms? I turn about 2500-2600 rpms right now with 3.55 gears and I am going to put 3.08 gears in about week from know. I usually get about 14 mpg on the highway this time of year at around 2500-2600 rpms. I do most of my driving on the highway so I am not too worried about acceleration and hauling power. My main reason is to get about 2mpg better and lower ring travel by turning those rpms at 55mph. Any info would be appreciated.

 

wow 2500-2600 rpms are high on the highway i have an automatic with 32"s i wish it were a straight drive so i could just go in a higher gear than my trans normally would. i decided im not going to put gears in because #1 its an auto #2 the cost of installation (i def cant do it myself) and #3 now that i got my highly restrictive exhaust out of the way so i have better acceleration. im thinking with stock tires u would get better than 2mpg on the highway

 

I have got stock size tires. Its just my final drive is 1:1 and the 3.55 rear end makes my rpms at 55mph about 2500-2600. I did the math and it seems I should lower those rpms to about 2100-2200 at 55. I don't want to get rid of the C6 because of its reputation and longevity. This solution to change gears seems the simplest because I just got new tires. With this, I should lower the rpms at 55 to the "sweet spot" in the 300's torque range.

 

have you done any mods on ur truck? to get better gas mileage? i was thinking if i were ever going to go on a road trip again i would just put my stock tires back on ( i have them on different rims) and an impact wrench speeds tire changing up ) i went down to charleston about a month ago and i averaged 11mpg with my 32s and stock exhaust

 

Should have said something earlier. I've got 2.5 from the y connector cat to the stock exit at the side with a flowmaster 70 series. That is the only cat I have. Other than that, everything else is stock and the engine is running clean and probably better than it ever has before.(I got the truck with 104,000 and now have 137,000).

 

Hi
IF any ones wants to sell a 308 ring gear and pinion gear set ring gear has 43 teath and the pinion gear has 14 teath. with carrier case please let me no
buckshot1417

 

so you got rid of the 2nd cat?

 

Hey. welcome to FTEF. I would have considered taking you up on that offer but I already ordered my 3.08 stuff a couple of days ago. No offense, but I kind of like to put new drive train parts in when possible.

Yep. Decided to take the chance of not passing emissions after consulting with others I know that have less emissions equip. than I do.

 

Hi
I have a 1991 ford 4x4 1/2 ton truck.with a 300-6 . I want to no if it' has a Dana 44 or Dana 60 differentail in to front. The wheel has 6 bolts not 8 ? I picked up another differentail for parts and they dont look the same.where doe's it say the part number (Dana 44)??? I need the carrier case for i can bolt my 3.08 ring gear to.

 

I run 255/60/15 tires (very close to stock height) and my rpm at 60 mph in 4th gear is 2500. I would expect a C6 to be 200-300 more than that due to converter slippage. I don't remember seeing what year your truck was, but EFI doesn't seem to care about gearing as much as a carb when it comes to mileage.

Have you considered an add on overdrive unit for the trans?