But you have to remember that the Boss motor has an 500 rpm additional rev capability, and it has slightly less torque through the midrange than a normal 5.0 motor, so gearing it to allow it to take better advantage of the rpm's would seem logical.

Could we summarize by stating that 3.55's in a normal 5.0 are equal to 3.73's in the Boss...

 

Possibly. On the other hand, the SVT PP option gives the GT500 a 3.73 gear, and IIRC, the motor spins to less than the 5.0. You'd think there that a lower gear ratio would be ideal for traction.

 

different transmission in the shelby and i assume ratios than a 5.0 as well...

 

After I said that, I realized that I wasn't awake enough to remember that. D'oh!

 

Thanks for the Shelby comment, I had forgotten to compare the Shelby gearing to the GT. Turns out that the 3.08 gears behind an MT-82 in the 5.0 is almost identical to the Shelby with 3.55's behind the Tremec TR6060:

2011 Mustang 5.0 w/Tune - redline @ 7200
3.08 @ 7200 rpms
1 = 51 mph
2 = 77 mph
3 = 110 mph
4 = 141 mph
5 = 187 mph
6 @ 80mph = 2000 rpm

2011 Shelby GT500
3.55 @ 6250 rpms
1 = 47 mph
2 = 79 mph
3 = 108 mph
4 = 141 mph
5 = 188 mph
6 @ 80mph = 1775 rpm

Now the question is, if the power was equal between the two above, which Transmission and Rear Gear Ratio would be more efficient at putting power down. More gear in the trans, or more gear at the rear?

 

More gear at the trans. Less work or power is needed to accelerate the driveshaft to a given road speed.

 

My wife's 2011 Accord coupe V6 has 4.33's in it

 

Just install the **** gears already.

 

Done, the 3.08's are installed, and I've adjusted the Tuner options for the gears and slightly shorter 285/35/19 tires I installed last week.

Through my 25-miles drive home from the shop today, I couldn't tell me difference in traffic, other than less noise at cruising speed. After a few heat cycles tomorrow, I will go out Saturday and give the gears a good testing provide some feedback.

 

As far as I can remember, your the first one to put in higher gears than stock. I am interested in how they perform.

 

Awesome...get the darn results so this can documented as a "win" or "fail" mod

 

Now that I've put 300 miles on the 3.08's, I can give some feedback.

Performance - Acceleration:

I feel like the car is quicker, especially from 0-100 mph. The car hooks up between the 1-2 shift much better with 3.08's, and 1st gear isn't as prone to spin the tires now. You also get to enjoy the acceleration a little more w/o having to shift from 1-2-3-4 so quickly.

The Drive:

The car feels less skittish with 3.08's than it did with 3.73's. With 3.73's the car felt more ADHD like, always ready to rev and spin the tires. There is less backlash in the drivetrain, and the car feels more refined with the 3.08 gears. Cruising along at 60mph+ works great with the torque the motor produces down low. The gear whine is gone, the engine noise is reduced, and the car is overall more enjoyable.

The Fuel Mileage:

Sadly, there is little fuel mileage to gain from 3.08 gears. This wasn't a goal of mine, but I was surprised to see my mileage stay practically the same with 3.08 and 3.73 gearing.

 

How much did it cost you to Go from 3.73 to 3.08?

Also what Is your average mpg?

I have the 3.73's and I am able to get 28mpg if I drive it easy and stay under 65 on the highway. That is 70% highway 30% city driving. That's me calculating the average after I fill up not going off what the dash says while I'm driving.

 

old timer cobra here <<<3:55s eaton diff x pipe shorty headers bbk intake all the old school go fast stuff and 3000 rpm = 90 mph car tops out at 140mph redline 4th gear
still gets 24 mpg going to vegas and 20 in the city <<<lead foot i have skipped second gear often in traffic but never started in second unless i was racing a camaro.

 

Cost of the gears and install kit was about $270, another $60 for 3-bottles of 75w-140 Royal Purple Max Gear Oil, and then another $300 for the labor. I used a speed shop I worked at years ago, and the mechanic gets the gears setup perfectly the first time around.

My average mpg with 3.73's and 3.08's is around 21mpg. I have a 75-mile round-trip commute 4-days a week, with about 65-miles of that being highway, maintaining speeds from 65-85 mph on average. What I find kills my cars average mpg is idle time at stop lights, stop and go traffic, and the ocassional stop in a fast food drive-thru.

I was able to get about 28mpg with 3.73's as well when setting the cruise between 60-65mph, and resetting the mpg counter while at speed. I was able to maintain a 28mpg rating for well over 20+ miles, but driving that slow for that long drives me nutty, so I never get that sort of mpg on a daily drive.

 

To the OP KN7671 ...

It's been a while now, how are you enjoying the 3.08 gears after living with them for some time?

 

Good thread here...


For what it's worth, my prior car was a 2005 GTO. 3.46 gears and a T-56. 400hp/400tq stock. Shift points were 46/65/101/143 when stock never topped out 5th, took it past 165 though. After mods that allowed it to rev 700rpm more, points were extended a bit.

I always felt they were spaced nicely. My Mustang has 3.31 gearing, and similar stock power. 420hp/390tq. On the first test drive I immediately noticed the shorter gearing. To the point that I assumed it already had 3.73s. Ive driven 3.73 coyotes since, and they are more like 4.10s on something that doesn't have odd transmission ratios.

I'll keep my 3.31s. While I desire more performance, I have no desire to change this.

 

Finally had the 3.08s installed.

Just doing the break-in, but so far I think I'll be very happy with them. Traction will be found where it was lacking before, no more gear whine, Highway cruising is at a reasonable RPM, and I should be able to get on it coming out of corners on the road course now in combination with the wavetrac differential I had installed at the same time.

Going with and sticking with the 18" tire size is what made the final decision to go all the way to 3.08. Initial impressions are favorable and so far happy with the decision.

Will get them a real workout at the Shelby Bash in a couple of weeks.

 

Didn't see this come back up a few months back, but it looks like you pulled the trigger on the 3.08's already.

I enjoyed my 3.08's for about 6-months when I decided to trade my '11 for a '12 Auto, which already comes with 3.15's. One thing I noticed with the 3.08's, is that getting out on the road in 1st gear and flooring it was more of a joy than work, as the car gets traction and accelerates.

If you are going to be tracking your car with 3.08's, I would suggest you get the transmission cooler Ford Racing sells for the MT82 that came with the Boss, more less an air scoop. I think the 3.08 gearing will cause a greater heat buildup under high-load conditions. http://www.fordracingparts.com/parts...KeyField=12495

 

Hey, Bryce, I ended up swapping gears last September. 3.73's are out and 4.56's are in now. Really helped my launches at the drag strip! Went from 1.90's to the sixty foot mark to high 1.6's to low 1.7's.