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Discussion Starter #1
Hey everyone, this is my first post so far (been reading the forums since I bought my Challenger in May '10)

Anyways, I've been keeping up with Hemiwoman and some of the others here who have been racing their SE's and I was just curious if anyone else has experimented with different rear ends and gear ratio's. I've got one of the 3.64 ratio setups on the way currently. Other mods (so far) include the obvious CAI, custom true dual exhaust done by a local shop, Eibach sportline spring kit and sway bars, pistol grip shifter, and I'll be ordering a Predator tuner as soon as I can.

Mainly just looking for tips as far as the installation I have ahead of me, what I can expect as far as drivability improvements...etc.

Thanks!
 

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Hey everyone, this is my first post so far (been reading the forums since I bought my Challenger in May '10)

Anyways, I've been keeping up with Hemiwoman and some of the others here who have been racing their SE's and I was just curious if anyone else has experimented with different rear ends and gear ratio's. I've got one of the 3.64 ratio setups on the way currently. Other mods (so far) include the obvious CAI, custom true dual exhaust done by a local shop, Eibach sportline spring kit and sway bars, pistol grip shifter, and I'll be ordering a Predator tuner as soon as I can.

Mainly just looking for tips as far as the installation I have ahead of me, what I can expect as far as drivability improvements...etc.

Thanks!
Something to keep in mind, you wont see drivability improvements, you'll see race ability improvements. Day to day will suffer. You'll basically be keeping the car at a higher RPM. Means you're in your power band quicker, but it also means lower mpg.
 

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Discussion Starter #3
Thanks for the reply, raceability should have been what I said in the first place. I know I'm gonna lose MPG's which really doesn't bother me much considering the car will be quicker. Exactly what I'm looking for.
 

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Yeap I've only heard of a couple of cases where lower gears helped MPG.
I drive many miles a day, so I'll wait until I retire the car from daily driver duty before I do that particular mod.
 

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although mine is not a challenger ('07 magnum SXT), i swapped in a 198mm axle assembly from an '06 300C AWD with 3.07 gears (direct swap). day to day driving, i notice better kick on downshifts. have not noticed any significant MPG loss. the gear swap, along with a Johan custom tune, has lowered my personal best from 15.309 to 14.672.
 

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the 3.64 will not give you huge gains and hurt your daily driving. i recommend the 3.07 gear for you SE 5-speed, but too late for that.

i bet bobbi would see quicker ET and higher MPH at the track with a 3.07 gear set. it would keep the motor in the power band better.

tips for install:

mobil 1 75w-90 gear oil (2 qts)
14mm allen wrench for the drain plug
new axles seals
 

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Something to keep in mind, you wont see drivability improvements, you'll see race ability improvements. Day to day will suffer. You'll basically be keeping the car at a higher RPM. Means you're in your power band quicker, but it also means lower mpg.
That depends. If the rear tire size is increased, the gear ratio should be changed to maintain the stock ratio.

Example:

If the stock size tire is 28" tall (215/65X17) and it's swapped for a 29" tall tire (255/45X20) the gear ratio has been changed by 3.57%.

The stock rear gear ratio of an SE is 2.87:1. 3.57% of that is 0.1025. Giving a new needed rear axle gear ratio of 2.9725:1.

Now, in reality, that's not much of a change that you'd feel, but the drive train will. Since we live in reality (for the most part), there are limits to available ring and pinions ratios. The closest to the new needed gear ratio is a 3.06:1 IIRC. It is about 2.9% lower in gear ratio then actually needed but in my opinion, it's better to be slightly over geared then slightly under geared.

Unless you drive nothing but at freeway speed, you'd never notice the rpm increase or the minor loss of fuel economy of the 3.06:1 gear ratio with the 255/45's.

But as to fuel economy loss, the 215/65 tire has a section width of 8.5" and the 255/45 has a section width of 10". An increase of over 17%. Basically, the wider tire creates a greater rolling resistance and the slightly over geared situation will help overcome that.


I hope that makes sense. Sorry, it's late and I'm babbling.

-Scott
 

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Discussion Starter #8
Considering the price I'm getting the carrier assembly for...if for any reason I'm not happy with the way it goes I won't be too upset. I work at a dealership (not Dodge unfortunately) so I have access to lifts and tools... :thumbsup:

On a sidenote, my Predator tuner is also on the way. If anyone's curious Late Model Performance has the lowest price I've seen with free shipping.
 

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I haven't noticed much in way of mpg change. I got 27 mpg driving from Charleston, SC to Ripley, WVa. coming home from vacation with air on and cruise set at 80mph. I get 19 -20 mpg around town. The biggest change is in rpms. 70 mph will be 2600 rpms. Used to be 2000. The 3.64 gears gets the car off the line faster. 60' was 2.3 - 2.45 with 2.87. 60' now is 2.13 - 2.25. I have run 94.22 mph in the 1/4. I go thru the 1/4 at 5300 rpms. When I was at Atco was going thru the 1/4 mile at 5500- 5800 rpms.
 

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although mine is not a challenger ('07 magnum SXT), i swapped in a 198mm axle assembly from an '06 300C AWD with 3.07 gears (direct swap). day to day driving, i notice better kick on downshifts. have not noticed any significant MPG loss. the gear swap, along with a Johan custom tune, has lowered my personal best from 15.309 to 14.672.
Fnkychkn's magnum and my car are pretty equal on the the drag strip. We ran each other twice at Atco. I got a hole shot on him and beat him even though his ET was 2/10's faster than mine. Next race he redlighted to beat me.
 

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Discussion Starter #11
Hemiwoman, I've been following your times and mods since I joined the forum. I'm hoping to break into the 14's eventually. So far my best time back in September (which my car was basically stock other than the intake) was a 16.00 and that was my first pass ever, haha. Have you made any passes since you added the 71mm throttle body? That's another thing on my to-do list...
 

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HVYMTL, my first pass ever was 16.05 with the car totally stock. 2nd & 3rd pass was 15.81. I made a few passes the day the 71mm TB was installed. Best that day was 14.89. But car started out running 15.00s early in the day. Now that we are snowed in won't get to the track till end of Feb in Florida. Next week my husband is going to start on my ported and polished lower intake manifold. I also have a 160degree thermostat that I just got from S/S Dodge to install.

I didn't get into the 15.0 and 14.9 till weather got really cool. Temps in 40s & 50s make the car go faster.
 

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HVYMTL, my first pass ever was 16.05 with the car totally stock. 2nd & 3rd pass was 15.81. I made a few passes the day the 71mm TB was installed. Best that day was 14.89. But car started out running 15.00s early in the day. Now that we are snowed in won't get to the track till end of Feb in Florida. Next week my husband is going to start on my ported and polished lower intake manifold. I also have a 160degree thermostat that I just got from S/S Dodge to install.

I didn't get into the 15.0 and 14.9 till weather got really cool. Temps in 40s & 50s make the car go faster.

These cars seem to REALLY be effected by the temps. Do you have the thermostat mod Hemiwoman? Who has that, SS Dodge? From what he has said, and his 0-60 times. it seems engine temp and air temp make DRASTIC changes in performance. I've noticed it with my car, as it is climbing to operating temps.
 

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These cars seem to REALLY be effected by the temps. Do you have the thermostat mod Hemiwoman? Who has that, SS Dodge? From what he has said, and his 0-60 times. it seems engine temp and air temp make DRASTIC changes in performance. I've noticed it with my car, as it is climbing to operating temps.
I just rec'd the thermostat from S/S Dodge. Haven't installed it yet. It is winter now and car is put away till end of Feb.

When I am racing and the temps are in 70s and 80s car runs slower times. I didn't start running 15.0s and 14.8s and 14.9s till temp were in 40s and 50s.

So we will have to wait and see how the car runs till it gets warmer outside. Right now we have 2+ ft of snow outside.
 

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Discussion Starter #15
Thanks for the input Hemiwoman, Got my predator in the mail yesterday :) Haven't tweaked much yet other than the 91 tune, increased shift firmness, raised rev limits, and turned off traction control. It's almost like driving a new car...

Ive got my axle seals and dif fluid already, just waiting for my 3.64 set-up to come in on Monday. Too bad it's too cold to get to the track next week, haha.
 

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although mine is not a challenger ('07 magnum SXT), i swapped in a 198mm axle assembly from an '06 300C AWD with 3.07 gears (direct swap). day to day driving, i notice better kick on downshifts. have not noticed any significant MPG loss. the gear swap, along with a Johan custom tune, has lowered my personal best from 15.309 to 14.672.
14.6 is a great time for a 3.5 ! It takes about 50 HP more to drop the ET down 1 second so the 305 HP Penastar SE should run about 14.6, the 250 HP SE ran 15.6. What are all the mods you have done to your Magnum to run 14.6 ? 5-speed ? Dual exhaust, headers ?
 

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14.6 is a great time for a 3.5 ! It takes about 50 HP more to drop the ET down 1 second so the 305 HP Penastar SE should run about 14.6, the 250 HP SE ran 15.6. What are all the mods you have done to your Magnum to run 14.6 ? 5-speed ? Dual exhaust, headers ?
not sure about LC, but AFAIK, 3.6L output in LX/LD trim is 290 hp.
yes, mine is a 5 speed. performance mods include; AirHammerHO CAI, hand-thinned throttle shaft, JBA shorty headers, Mopar/Borla cat-back dual exhaust, 3.07:1 axle, Johan (Diablosport) custom email tune, Hoosier racing slicks (borrowed & can't remember the size), interior lightened for racing.
for a complete list of mods, see here: Izzy pics - LX Forums | Dodge Charger Challenger Magnum | SRT8 | Chrysler 300 Forum
 
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