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Discussion Starter · #1 ·
This was also posted in the Real World Mileage with the V6 Manual thread.

Sorry to double-post, and many of you might not care about this info one way or another, but I hope it does help someone in making a decision, if they're considering deeper gears.

I conducted two more performance vs fuel economy experiments this weekend with my V6 manual w/2.73's:

1. 188 mile one-way trip from 135 ft elevation to 4000+ then down to sea level, with a majority of the trip being up-hill (very gradual over 110 miles, then 6% grade up to 4000+ ft, alternating with 1000-2000 ft declines then back up again several times before finally descending to sea level rather quickly): I kept the car in 4th a majority of the way (3000 RPM @ approximately 73 MPH) except in the hills, where I kept the engine speed between 3000-4000 with more than a handful of leaps up to 6000 just for high-speed fun on the open straight-aways. The trip was completed on 8 gallons of gas (rounded from 8.xxx tenths). Manually calculated = 24 MPG. The computer readout was completely unreliable with the up-and-down elevation changes.

2. Trip #2: return trip but without the stops along the way, thus 183 miles; sea level with rapid ascent to 4000+ feet with alternating elevations @ 6% grade, followed by rapid descent to around 500 ft then a very gradual descent to 135 ft over the next 110 miles; "spirited" driving between 80-120 MPH on approximately 75 miles of the trip, @ 3000-6000 RPM, with a majority @ 73 MPH @ 2500 RPM (5th gear instead of 4th this time). The return trip was completed on 7.5 gallons of gas (calculated manually) = 24 MPG again.

Given these results in extreme elevation changes, the 29 MPG I had attained last week was not a fluke. A distance of 233 miles was traveled @ 3000-4000 RPM on a much flatter route (no mountains). The vast majority of the trip was a slow, unnoticeable descent from 1600 ft to 135 ft.

What this tells me is that in the proper elevations/outside environment/driving habits, 3.31's, 3.55's and 3.73 gears (or deeper) will not necessarily bury the fuel economy of the V6, though it will drop a little. Many of you already know this, but I had to find out for myself without actually spending money on the gears. Admittedly I went deeper in the RPM's than the gears would have caused (in 6th, anyway), but I had to see the results of driving nearer the car's optimum HP/TQ range, to see if that would be any more beneficial.

I suspect that had I maintained 2500-3000 RPM over relatively flat elevations for another 100-200 miles, the fuel economy would have corrected itself to the neighborhood of 27-30. I have no reason to doubt this at all. The V6 loves distance. The flatter the better.
 

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This was also posted in the Real World Mileage with the V6 Manual thread.

Sorry to double-post, and many of you might not care about this info one way or another, but I hope it does help someone in making a decision, if they're considering deeper gears.

I conducted two more performance vs fuel economy experiments this weekend with my V6 manual w/2.73's:

1. 188 mile one-way trip from 135 ft elevation to 4000+ then down to sea level, with a majority of the trip being up-hill (very gradual over 110 miles, then 6% grade up to 4000+ ft, alternating with 1000-2000 ft declines then back up again several times before finally descending to sea level rather quickly): I kept the car in 4th a majority of the way (3000 RPM @ approximately 73 MPH) except in the hills, where I kept the engine speed between 3000-4000 with more than a handful of leaps up to 6000 just for high-speed fun on the open straight-aways. The trip was completed on 8 gallons of gas (rounded from 8.xxx tenths). Manually calculated = 24 MPG. The computer readout was completely unreliable with the up-and-down elevation changes.

2. Trip #2: return trip but without the stops along the way, thus 183 miles; sea level with rapid ascent to 4000+ feet with alternating elevations @ 6% grade, followed by rapid descent to around 500 ft then a very gradual descent to 135 ft over the next 110 miles; "spirited" driving between 80-120 MPH on approximately 75 miles of the trip, @ 3000-6000 RPM, with a majority @ 73 MPH @ 2500 RPM (5th gear instead of 4th this time). The return trip was completed on 7.5 gallons of gas (calculated manually) = 24 MPG again.

Given these results in extreme elevation changes, the 29 MPG I had attained last week was not a fluke. A distance of 233 miles was traveled @ 3000-4000 RPM on a much flatter route (no mountains). The vast majority of the trip was a slow, unnoticeable descent from 1600 ft to 135 ft.

What this tells me is that in the proper elevations/outside environment/driving habits, 3.31's, 3.55's and 3.73 gears (or deeper) will not necessarily bury the fuel economy of the V6, though it will drop a little. Many of you already know this, but I had to find out for myself without actually spending money on the gears. Admittedly I went deeper in the RPM's than the gears would have caused (in 6th, anyway), but I had to see the results of driving nearer the car's optimum HP/TQ range, to see if that would be any more beneficial.

I suspect that had I maintained 2500-3000 RPM over relatively flat elevations for another 100-200 miles, the fuel economy would have corrected itself to the neighborhood of 27-30. I have no reason to doubt this at all. The V6 loves distance. The flatter the better.

I went to 3.73's in my 2011. At 80mph I'm spinning at about 2500rpm +/- 100rpm. I did a run from Orlando, FL - Atlanta, GA non-stop and I think still got ~25mpg. I'm running the 93 octane race tune so I dont know if that has anything to do with the gas mileage.
 

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Discussion Starter · #3 ·
I'm running a 91 octane Street tune.

Most of our speed limits out here are 70-75 MPH, so I experiment in the range of (simulated) 80 MPH RPM's (2000-2500) and higher (3000-4000), as almost no one out here really drives as slow as 70.

What is the majority speed limit between Atlanta and Orlando (or other Florida cities)?
 

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I'm running a 91 octane Street tune.

Most of our speed limits out here are 70-75 MPH, so I experiment in the range of (simulated) 80 MPH RPM's (2000-2500) and higher (3000-4000), as almost no one out here really drives as slow as 70.

What is the majority speed limit between Atlanta and Orlando (or other Florida cities)?
Along I-75, it would be 70mph.

Thanks for that analysis. I am ready to pull the trigger on 3.73 gears...although all my friends say it pulls hard enough stock :)
 

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Along I-75, it would be 70mph.

Thanks for that analysis. I am ready to pull the trigger on 3.73 gears...although all my friends say it pulls hard enough stock :)
Oh you'll notice a difference...
Put 3.73 gears in with a tune and with the street tires, you'll get major wheel hop majority of the time on launches. Put upgraded Lower Control arms on and launch at a lower RPM you'll be doing a nice peel out in first, and also as you hit second gear, not a chirp, a nice long peel out that will plant you in the seat. Then, get some good performance tires, and you'll feel the A$$ plant in the seat, but it will be a chirp in second and improve your 1/4 mile times as well.
 

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I went to 3.73's in my 2011. At 80mph I'm spinning at about 2500rpm +/- 100rpm. I did a run from Orlando, FL - Atlanta, GA non-stop and I think still got ~25mpg. I'm running the 93 octane race tune so I dont know if that has anything to do with the gas mileage.
I put my V6 Mustang convertible on the highway for 110 miles last week - gas station on ramp to gas station off ramp. All of my other driving had been mostly city driving with no more then 5% freeway driving. The first 10 miles was 65 - 70 mph. The next 100 miles was cruise control 75 mph. The terrain is up and down foothills - almost no net elevation change. The mpg is calculated from miles driven and gallons to 2 decimal points and was 31.39 mpg. Although some of the hills were reasonably steep, the transmission downshifted very few times. The differential is 2.73 with the automatic transmission. The car was running the stock tune and 87 octane fuel. I was very happy with the performance.
 

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Oh you'll notice a difference...
Put 3.73 gears in with a tune and with the street tires, you'll get major wheel hop majority of the time on launches. Put upgraded Lower Control arms on and launch at a lower RPM you'll be doing a nice peel out in first, and also as you hit second gear, not a chirp, a nice long peel out that will plant you in the seat. Then, get some good performance tires, and you'll feel the A$$ plant in the seat, but it will be a chirp in second and improve your 1/4 mile times as well.

I gotta say my '12 v6pp already lays a healthy amount of rubber going into second- and that's with the 255/40 19 inch summer tires. Got to imagine that the base pizza cutters would do a decent roast!
 

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Has anybody compaired 87S to Stock tune for mpg. As far as FPG (FUN PER GAL) the 87S is a blast (mine was tweeked some extra for harder shifts & higher shift points )
I just hate switching back to stock to compair MPG's it's so much fun with the 87S (tweeked). Getting 21-22 city/mix.
But if I took a long trip I think I might switch back to Stock just to save on gas.
 
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