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Discussion Starter #1
Has anyone put an 8 speed automatic in a car that came with a 5 speed? In particular a 2013 SRT8. What would be the complications? Rear end gearing wrong? Driveshaft need to be different? Changes to the electronics? Will the 6th, 7th, and 8th gears show up correctly in the gage cluster when using paddle shifting? How expensive would this be? It seems like one of the best mods you could do, or am I wrong?
 

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Has anyone put an 8 speed automatic in a car that came with a 5 speed? In particular
a 2013 SRT8. What would be the complications? Rear end gearing wrong? Driveshaft need to be different? Changes
to the electronics? Will the 6th, 7th, and 8th gears show up correctly in the gage cluster when using paddle shifting?
How expensive would this be? It seems like one of the best mods you could do, or am I wrong?
Floor pan of car is different, all the electronics would be non compatible. Basically by the time you made it work
you probably would be better off buying a newer model. These things get more and more complex each year. It
was hard enough back in the day to swap say a 700R4 or an older LT1 EFI engine into a hot rod and it took years
for companies to make harnesses and computers to "retrofit" those simple engines and transmissions. Now the coding
is all locked down and they change so much within a few model years that rarely anything can be swapped.
 

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changing gears

You might want to swap the rear diff instead, like I did, swapping the 3.07 for 3.90 r&p. I thought about the 8 speed auto too and thought it would be a thing to have, so I went and drove a scat pack auto as soon as the dealership got one to find out if I should trade my '09 SRT8 with the NAG1 for an 8 spd model. Here are the reasons I stuck with the 5 speed: with the 3.90 (3.92?) gearset in my car the 8 spd didn't feel like it pulled as hard, and you could barely feel the gear changes. On the downshifts the 5 speed has a wider gear to gear ratio compared to the 8 spd, meaning if you floor it while at cruise the 5 speed has a more noticeable downshift and pulls harder. So if you like the old school muscle car feel, and the chirp of the tires on a gear change, the 8 speed's "pulled by a rubber band" feel might be a disappointment.
 

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The A8 is anything but disappointing when you're running it through the gears at WOT.


"Pulled by a rubber band"...........really! LMFAO


To the OP, as others have stated, cost and complexity of the swap would be BIG.
 

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Discussion Starter #5
How about a rear gear swap to a 3:73 or 3:55. That could be an interesting change. Speedlogix sells a 3:73 complete unit.
 

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I did the 3.73 swap with my 5 speed auto. Makes a world of difference in seat of pants feel, gas mileage (before anyone gets on here and says you should have a bought a Toyota if your worried about mpg-I already know) and also cruise rpm's. Like everything else we do to these toys, it is expensive. Running high boost as I am now, not sure if I would do it over. Traction is a big issue, will roast tires at will and trying to get a decent start from dead still is impossible. I read something somewhere from the Ken Belle people, "do not swap gearing if your going to boost". Of course that was after I had already done so. Day late, dollar short-that's me. Just my 2 cents.
 

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i guess I need to clarify my post. I am not saying the A8 isn't bad ass, I am also not saying one auto trans. is better than the other or comparing the two. What I am saying is: 1) if you change then diff from stock to 3.90 you will see a huge difference, 2) if you then drive that car to the dealership and test drive an A8 car and are expecting some kind of improvement or increase in performance, you WILL be disappointed. 3) after driving the geared A5 car, the A8 will feel like one long smooth pull (rubber band), rather than individual gears with noticeable shifts, and on downshifts the wider ratio between gears will be more noticeable/not as smooth as the A8. other than that, just trying to give useful info to those who are having the same thoughts about mods that I have had. FWIW my E.T. dropped by more than a full second with only the rear end swap and Diablosport canned tune (needed to reprogram drive ratio). the car now tops out at 155mph instead of whatever it did before, cruise at 80 mph is about 3500rpm, and WOT upshift to 5th is at 120mph. with the 245/45-20's in back it would break the tires loose and slide the tail to the right on the 1-2 shift and then bark hard on the 2-3. you can get new L.S. diff's from steve white motors, and if you're going to tackle it yourself: 1) accessing the 2 bolts on top of the diff is too tight to get most tools in due to how close the body is to the diff. 2) after the gear change the car will NOT be driveable without changing the gear ratio in the PCM with a tuner, or tow to dealer for reflash. it's not just a matter of the speedo being off.
 

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I agree with what you've said Heyw00d. What I wish for is either a 3.23 or 3.55 Getrag. At this point in my life I would go with the 3.23 with the A-5. But then again maybe the 3.55! What doesn't Mother Mopar offer these ratio's is beyond me. And I don't mean stock ratio's I understand about the EPA and gas mileage estimates, I mean in the aftermarket Mopar Performance Parts area. Does this make sense or am I just hung up in the sixties and seventies? Please help. I'm going down to the basement and grab another beer.
 

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when I chose the 3.90 I knew I was going to change the rear wheels to 22x10 so I could get more traction using 285/35-22 nitto 555's. I picked up .2 @ 330' by getting off the line better, but the taller tire cancelled it out and my 1/4 mile et's were the same. If you were considering a 3.55 you might get to the same place by doing the 3.73 and switching out the rear wheels to taller ones. I had 3.55's in my 71 el camino and it was great with the 3spd auto, but I think you can go deeper with the A5 and not regret it. I had to drive 120 miles round trip, to see my daughter on weekends, almost every week for a couple of years and the car wasn't straining itself at all and cruised nicely at 80 on the freeway and in temps over 110 on regular basis.
 

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Love my A8 more every day!

The other night on the expressway at 70 plus had to MASH the brake pedal. WOW! the trans read the effort I was putting into this stop and downshifted through the range to give some serious engine braking (I'll guess about close to max. rpm down through the range). I would say it read my mind but it thinks faster! I was in sport mode, 7th gear at the time.:rocket:
 

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I did the 3.73 swap with my 5 speed auto. Makes a world of difference in seat of pants feel, gas mileage (before anyone gets on here and says you should have a bought a Toyota if your worried about mpg-I already know) and also cruise rpm's. Like everything else we do to these toys, it is expensive. Running high boost as I am now, not sure if I would do it over. Traction is a big issue, will roast tires at will and trying to get a decent start from dead still is impossible. I read something somewhere from the Ken Belle people, "do not swap gearing if your going to boost". Of course that was after I had already done so. Day late, dollar short-that's me. Just my 2 cents.
I did the same thing, 3.73 then SC, Cant stop spinning.. back to 3.06 for me. 3.73 for sale soon.
 

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I bought a new getrag and upgraded clutch pack. Sold my original one.
I still have my stock peg-leg (I think) I've sold so many parts off this car I have to check and see what I do have that came off of it. Can't go back to the peg-leg so if I change out I will have to buy either new or used Getrag from someone. Dam I wished Mopar would offer something between 3.06 and 3.73. Had a 3.55 in a 4 speed '73 Road Runner, the perfect combo for me.
 

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I still have my stock peg-leg (I think) I've sold so many parts off this car I have to check and see what I do have that came off of it. Can't go back to the peg-leg so if I change out I will have to buy either new or used Getrag from someone. Dam I wished Mopar would offer something between 3.06 and 3.73. Had a 3.55 in a 4 speed '73 Road Runner, the perfect combo for me.
I almost bought Dynatrac, I think it was.. They have 3.25 or 3.23.. But 7k ish.. Maybe some day.
 

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I almost bought Dynatrac, I think it was.. They have 3.25 or 3.23.. But 7k ish.. Maybe some day.
7k for a rear gear? You got to be kidding! I'm out. Only if I win the lottery, which I never buy any lottery tickets so that ain't happening. Will just run this 3.73 and enjoy the tire smoke and buy more 93 octane!
 

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7k for a rear gear? You got to be kidding! I'm out. Only if I win the lottery, which I never buy any lottery tickets so that ain't happening. Will just run this 3.73 and enjoy the tire smoke and buy more 93 octane!
Yep me too.. 7k is for whole setup, axles, pumpkin, gears driveshaft... I'll keep the 3.06 and throw more HP at it..
 

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7k for a rear gear? You got to be kidding! I'm out. Only if I win the lottery, which I never buy any lottery tickets so that ain't happening. Will just run this 3.73 and enjoy the tire smoke and buy more 93 octane!
Wonder how much just for pumkin?
Different spline I think .. Just looked and dynatrac comes in 3.54. Driveshaftshop has a 9" conversion but still big $$$
https://www.dynatrac.com/axle-assemblies/dodge-challenger-lc-lx-pro-60-irs/pro-60-irs-with-truetrac.html
 
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