3.15 gear?

[mjhousto]

There are a few threads that compare the 3.15 AT gearing to the other ratios that are available. From what I've read the 3.15 is actually shorter than the manuals 3.31 in 1st and 6th gear due to the difference in the gears between 6R80 and the MT82. For 2nd through 5th they are similar, but the manual is slightly shorter.

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[DR_]

The 3.73 only comes on the manual performance pack but it would still fit on the auto. I don't know if it would cause other issues with the programming of the auto transmission, cruise control, etc. I wouldn't want to be the guinea pig on the new auto transmission and would wait until one of the bigger shops does one first.

 

[Gdyup50]

OK well thanks alot for your help, I've learned alot...

The 3.73 only comes on the manual performance pack but it would still fit on the auto. I don't know if it would cause other issues with the programming of the auto transmission, cruise control, etc. I wouldn't want to be the guinea pig on the new auto transmission and would wait until one of the bigger shops does one first.

 

[Herr_Poopschitz]

FYI, I think the differentials used w/ the 3.15s is unique. All other ratios use a different traction lok (clutch style limited slip diff), w/ the 3.73s using the torsen, so it wouldn't be a simple matter of swapping just the gears. As recommended, look for the whole '3rd member', 'pumpkin', etc.

I also believe there is no way to correct the speedometer just yet, but a solution is in work...

 

[Sal33n]

Spend your money on the other upgrades most people do first (Exhaust, CAI, tune) and see if it's fast enough for you. Then if you are not satisfied look into the gears. I say this because there is more hassle to changing gears (not including getting the speedometer corrected) then there is for the other basic mods.

 

[Need4Speed15]

With the gearing in the auto, 3.15's are a good gear and allows you to finish the 1/4 mile in 3rd. No need to change them!

 

[1320']

With the gearing in the auto, 3.15's are a good gear and allows you to finish the 1/4 mile in 3rd. No need to change them!

Bingo.

3.55's will be more fun on the street but may result in a shift in the fourth before the end of the run

 

[Old Car Guy]

Gears....

Getting the pinion preload and the carrier backlash (controls how the gears mesh together) is tricky. I have had problems with this in prior cars. This time I hope to find the holy grail (3.73 w/torsen) pumpkin and swap the whole thing over.

And some can be more problems then others, I had one installed at a Ford Dealer, and it made to much Noise for me...... If I was going to do another gear change, I would find a whole pumpkin also, this time...... John

 

[Herr_Poopschitz]

Bingo.

3.55's will be more fun on the street but may result in a shift in the fourth before the end of the run

...and this is bad? I don't understand this reasoning...please explain...

 

[Need4Speed15]

...and this is bad? I don't understand this reasoning...please explain...

Extra shift takes time and puts you going through the traps at a less the ideal rpm. We are just talking 1/4 mile here, 3.55's on the street would be fine and make the car "feel" quicker.

Anyway, if you look at the 11-14 cars most hardcore N/A guys either leave the stock 3.15's or at most switch to 3.31's which still allow the car to go through the traps in 3rd.

 

[1320']

...and this is bad? I don't understand this reasoning...please explain...

No problem!

Ideally you want to cross the line at maximum power, as near as possible to either peak power or red line. It is one of the reasons why when people make modifications to an engine that results in the peak power or red line moving higher into the RPM range, you typically see people readjust their FDR(final drive ratio) and tire size to make sure they're crossing the stripe at the big end at the highest RPM possible.

3rd gear in the 6R80 is 1.52:1, when combined with the 3.15 gear ratio results in a effective final gear in 3rd of 4.78 which is ALOT of gear for any car, even the Cobra Jets with a 3sp auto do not run that aggressive of a rear end. With 3.15's the 5.0 is screaming at the end of the run, thus...theoretically at max power depending on your mods.

If you shift into 4th your effective power drops as will your time due to the drop in power and time for the shift.

The 6R80 has REALLY aggressive 1st and 2nd gear ratios in the transmission. Torque multiplication goes through the roof, and shorter FDR gears only magnifies this effect.

Lets just say you have certain mods on your car, we'll use a 2011-14 car as an example with CJ intake, manifold, LT's, CJ Cams and such and you're making 475 WHP at 6,600 RPM. You want to cross the line as close to 6,600 RPM as possible. You adjust this by manipulating the shift points to keep the car in third as long as possible.

TL;DR...you want as FEW shifts as possible in a 1/4 mile run and want to making as close to max power at the end as possible

 

[Slade]

I have a 3:15 auto and just finished a 3600 mile road trip. I didn't baby it and had lots of fun. I got 26.5 mpg average for the trip. Just saying.

 

[Herr_Poopschitz]

No problem!

Ideally you want to cross the line at maximum power, as near as possible to either peak power or red line. It is one of the reasons why when people make modifications to an engine that results in the peak power or red line moving higher into the RPM range, you typically see people readjust their FDR(final drive ratio) and tire size to make sure they're crossing the stripe at the big end at the highest RPM possible.

3rd gear in the 6R80 is 1.52:1, when combined with the 3.15 gear ratio results in a effective final gear in 3rd of 4.78 which is ALOT of gear for any car, even the Cobra Jets with a 3sp auto do not run that aggressive of a rear end. With 3.15's the 5.0 is screaming at the end of the run, thus...theoretically at max power depending on your mods.

If you shift into 4th your effective power drops as will your time due to the drop in power and time for the shift.

The 6R80 has REALLY aggressive 1st and 2nd gear ratios in the transmission. Torque multiplication goes through the roof, and shorter FDR gears only magnifies this effect.

Lets just say you have certain mods on your car, we'll use a 2011-14 car as an example with CJ intake, manifold, LT's, CJ Cams and such and you're making 475 WHP at 6,600 RPM. You want to cross the line as close to 6,600 RPM as possible. You adjust this by manipulating the shift points to keep the car in third as long as possible.

TL;DR...you want as FEW shifts as possible in a 1/4 mile run and want to making as close to max power at the end as possible

Sorry to disagree, but the proposed 10 speed auto is going to smoke the 6R80, all w/ more shifts. The number of shifts has nothing to do w/ it, it's the mount of time spent in the rpm range where engines produce maximum hp.

A CVT or a clutch as used in Top Fuel is the ideal method of transferring power for acceleration....when applying this to an auto, effectively, the more shifts the better...assuming no torque mgmt is killing the shift times.

Take your last sentence...if what you're proposing is true, why not have a single speed gearbox...launch at idle, and cross the line at max hp...or, as actual drag racers do, a few hundred rpm past peak, depending on power curves?

To go fast, gear the car to use 4 gears by the end of a run w/ a looser than stock converter. Will be quicker than using only 3...promise.

 

[Need4Speed15]

Sorry to disagree, but the proposed 10 speed auto is going to smoke the 6R80, all w/ more shifts. The number of shifts has nothing to do w/ it, it's the mount of time spent in the rpm range where engines produce maximum hp.

A CVT or a clutch as used in Top Fuel is the ideal method of transferring power for acceleration....when applying this to an auto, effectively, the more shifts the better...assuming no torque mgmt is killing the shift times.

Take your last sentence...if what you're proposing is true, why not have a single speed gearbox...launch at idle, and cross the line at max hp...or, as actual drag racers do, a few hundred rpm past peak, depending on power curves?

To go fast, gear the car to use 4 gears by the end of a run w/ a looser than stock converter. Will be quicker than using only 3...promise.

Sticking to the original question which was a 3.15 gear with the 6R80, its a great gear. All you need to do is look at the history, past 5 years with these cars. We are not talking about a new combo here, these transmissions have been around for years.

Oh and for the record, most very high hp track cars use powerglide transmissions (which are 2 speeds)! The record setting JPC turbo coyote uses a powerglide, yep only 2 gears...1 shift. He went 7.75 at 185 this past weekend at NMRA. Beefcake also uses a powerglide in his car, 8.18....1 shift.

Anyway, back to the original topic. OP, no need to swap the 3.15 gear!

 

[Herr_Poopschitz]

Oh and for the record, most very high hp track cars use powerglide transmissions (which are 2 speeds)! The record setting JPC turbo coyote uses a powerglide, yep only 2 gears...1 shift. He went 7.75 at 185 this past weekend at NMRA. Beefcake also uses a powerglide in his car, 8.18....1 shift.

Loose converters that you wouldn't use on a dd. The slippage keeps the engine in the powerband...for the record.

Seems everyone's doing it wrong...all you need is a 'glide in your street car.:doh:

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