2009 GT v8 5 speed with 3:31 gears from The factory?

[GriffX]

Hard to find a general rule. In Germany at least 50% of all crossings have 4-way Stop signs, so 3.73 was way more pleasant to drive with the TR3650 in first gear. On the other hand the Autobahn is often limited to 80 MPH so you drive long distances with 85 and I would like to have a 2nd overdrive or 6th longer gear for this. Ying and Yang

 

[Dino Dino Bambino]

I've always felt that the stock 3.55 axle gear ratio on the 05-06 GT was ideal on a stock cammed car. My only gripe, and it's only a minor one, is that there isn't another transmission ratio (0.82:1) to split the yawning gap between the 1.00:1 4th and 0.68:1 5th. The outcome would then be a 0.82:1 5th and a 0.68:1 6th.

 

[Pentalab]

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Nailed it. This is exactly what you want for a LSD. The oem setup with the clutch packs is fubar and failure prone.
The Tru-trac is the real deal, and has a 3.5:1 bias ratio...which is ideal for street, strip, auto cross, or a road course.
BUT it uses plane jane dino oil, like 75W-140. NO synthetic, and NO friction modifiers. I would install a rear axle catch can though.

 

[brasil]

..the 3.73 is nice, when we are talking about fast acceleration. But around town..with a 5 speed manual, the 3.31 is a nicer ratio. Because you don´t have to slip the clutch soooo much. The 3.73 is like a bullitt.. the 3.31 is way smoother ( From what I noticed )

 

[thirwin]

My ‘07 has 3.31 gears and I’m happy with the gas mileage that I get, 26 hwy and 21 city; and it’s plenty quick for me.

 

[whitmanink]

I've always felt that the stock 3.55 axle gear ratio on the 05-06 GT was ideal on a stock cammed car. My only gripe, and it's only a minor one, is that there isn't another transmission ratio (0.82:1) to split the yawning gap between the 1.00:1 4th and 0.68:1 5th. The outcome would then be a 0.82:1 5th and a 0.68:1 6th.

i agree somewhat with this,, if it wernt for 3rd being so long , and puts u soo low in the rpm\ hp range , it really makes the car slow because of that

 

[Dino Dino Bambino]

i agree somewhat with this,, if it weren't for 3rd being so long , and puts u soo low in the rpm\ hp range , it really makes the car slow because of that

I see your point. It depends on the type of use you're putting the car through. On a road course where you want quick acceleration coming out of turns, a 4.10 ratio axle gear would be more suitable and especially so if the engine's been cam swapped (less low rpm torque). On the dragstrip, a 3.55 axle gear will allow you to hit the 1/4 mile trap at the top of 3rd gear thus requiring only two gear changes (as in my case) but again, it isn't a case of one size fits all. The combination of performance mods, tire size, transmission ratios, and type of use will dictate the optimum axle gear ratio.
One thing's for sure, the factory 3.31 ratio on 07-09 GTs is way too tall unless you have a positive displacement supercharger, and Ford only opted for that to improve highway fuel economy.

 

[Pentalab]

I see your point. It depends on the type of use you're putting the car through. On a road course where you want quick acceleration coming out of turns, a 4.10 ratio axle gear would be more suitable and especially so if the engine's been cam swapped (less low rpm torque). On the dragstrip, a 3.55 axle gear will allow you to hit the 1/4 mile trap at the top of 3rd gear thus requiring only two gear changes (as in my case) but again, it isn't a case of one size fits all. The combination of performance mods, tire size, transmission ratios, and type of use will dictate the optimum axle gear ratio.
One thing's for sure, the factory 3.31 ratio on 07-09 GTs is way too tall unless you have a positive displacement supercharger, and Ford only opted for that to improve highway fuel economy.

Dino, how fast does the manual 5 speed go, when at say 6000 - 6200 - 6500 RPM in 3rd gear, with the 3.55 gear ??

 

[Dino Dino Bambino]

Dino, how fast does the manual 5 speed go, when at say 6000 - 6200 - 6500 RPM in 3rd gear, with the 3.55 gear ??

With stock sized 235/55R17 (765 revs per mile) or optional 255/45R18 tires (770 revs per mile), gearing with 3.55 (39/11) ratio axle gears is 16.7mph/1000rpm in 3rd. Therefore:

6000rpm = 100mph
6600rpm = 110mph

If you multiply the tire revs per mile by the axle gear ratio, you get the engine rpm at 60mph in the direct 1.00:1 transmission ratio (4th in the TR3650).

 

[Pentalab]

With stock sized 235/55R17 (765 revs per mile) or optional 255/45R18 tires (770 revs per mile), gearing with 3.55 (39/11) ratio axle gears is 16.7mph/1000rpm in 3rd. Therefore:

6000rpm = 100mph
6600rpm = 110mph

If you multiply the tire revs per mile by the axle gear ratio, you get the engine rpm at 60mph in the direct 1.00:1 transmission ratio (4th in the TR3650).

On my 2010 auto, with my 3.31 rear gear, I'm barely 145 kph @ 6 krpm....in 3rd gear. 2nd gear in the auto is 14% lower than 2nd gear on the manual. 3rd gear in the auto is 16.5% lower than 3rd gear on manual. I worked this out 10 yrs ago, and u would require a 3.73 rear gear in the manual for ur 2nd gear to equal 2nd gear in the auto with it's 3.31 rear gear. You would require a 3.90 rear gear in the manual for ur 3rd gear to equal the 3rd gear in the auto with it's 3.31 rear gear.

Where I lose it in the auto is in 4th gear (1:1 ratio)....and the 3.31 rear gear. Then it's 150 mph @ 6 krpm...in 4th gear. When it upshifts from 3rd to 4th, the rpm drops like a rock, like down to 3.5 krpm....then it's a slog getting back up to 5+ krpm. But with blower, LT's and the DSS-DS, it's a non issue for street use.

Bottom line is, I would have to be in 4th gear to do the 1/4 mile. What would work with the auto's gearing is to use a 4:10 rear gear. Then it's 121 mph @ 6 krpm. Right now it's 125 mph @ 5 krpm.