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Am I the only one not that impressed with the difference going from 3.06 open to 3.92 Getrag in an automatic R/T? I guess I'm so used to driving with 4.10's in my other car that it's just not a big deal. This is a list of what I like and don't like.

Like:
1. Power is there almost instantly
2. Can leave it in drive and always have power, no lugging around or shifting into a high gear during acceleration
3. Should drop my 1/4 mile time (obviously)

Don't like:
1. Exhaust tone doesn't sound anywhere near as badass as it did (higher RPM's)
2. Highway speed RPM
3. Not enough difference in acceleration to justify the fuel mileage decrease
4. Getrag humming sound
5. Was a B1TCH to install


Finally got a chance to floor it in manual mode today. First gear was spinning, but I guess wheel hopping? Tires were like "chirp chirp chirp chirp". Second gear screeched, and third gear took off. Gets to 100mph faster, but to be honest I'd rather have my original open 3.06 setup back in. I might end up swapping the Getrag gears for 3.55's sometime soon. Overall, not impressed.

I might just switch my Diablo 93 tune back to the factory 87 tune. The gears should make up for the difference, I really don't think the Diablo 93 tune does jack sh-t. Would turning MSD back on give me a couple more MPG with the 3.92 setup? Damn I miss the way my R/T sounded before the swap...


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I got beat up quite a bit when I posted "cons" several times against the swap. I offered my 2 cents whenever I saw someone on the forum considering doing it. I traded out my '08 peg leg for a Getrag, but stuck with the 3.06 gear, precisely because I didn't want the extra RPM on the highway, the reduction in gas mileage, and the additional engine noise for MAYBE a tenth or two at the strip. (Where I might appear maybe twice a year.) You're not the first guy I've heard that's disappointed with the swap. The 3.92 revs 22% higher than the 3.06 at a given speed. THAT'S what you'll notice mostly, and have to learn to live with unless you don't care, and live only to drag race.
 

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Good info in this thread glad you are liking your new gears. I am new to the modern muscle but some things like gear ratios are still shared with old school. I have 4.11s in my Barracuda and they are just plain fun when you hammer it.

I am curious have you upgraded your IRS with heavy duty parts? Heavy cars and 3.92 gears can really be hard on the driveshaft and U joints.
 

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Might consider doing the zero-camber mod in the rear. Whatever tires you got back there now, will be magnified in traction, once you eliminate the static camber. That ought to bring "some" of that 1st gear capability back into the picture to help your 0-60 time.
 

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There is definitely a "sweet spot" on gear ratio.

A friend of mine and I both had Trans Ams, mine was a '79, and his was a '78. Both were identically equipped when new, 403 Olds, turbo 350 with an insane 2.41 posi rear end. One of the first mods I made was a change to 3.21 gears. Even with the 2.41 gears, a few mods like a set of headers and dual exhaust had it doing very nice burnouts, so I figured the 3.21 would be a good change, and I was very happy with it. I came into some money later on and went to 3.51's and it was too much, and went back to the 3.21 gears. My friend went with 3.90 gears as his first mod, and it was just insane. The car was almost impossible to hook up, especially after we both changed cams and intake manifolds. I would and could destroy him at the strip. If he didn't want tire melting spin, he had to drive it gently off the line, while I could hit it pretty good. I had my car in the mid 13's pretty much 3 months after I got it. He was unable to crack a 13 until just before he gave up on the 3.90s. After about a year, he went to 3.21 and immediately admitted the car was much more pleasant to drive in any important way. I drove a friend's 79 Camaro with 3.73s recently and IMHO, it was overgeared and was nothing like the super torque monster 403's were/are even with those high ratio gears. A T/A with a 403 done right is an awesome street set up. I sold my T/A almost 30 years ago, and still miss that amazing throttle hit it had. I was happy to see my T/A is back on the road, mostly in primer, but it seems to be running well. If I only had the money, I would buy a '77-78 California 403 car and build it just like my old one, with a few minor changes. Just as quick as my R/T, but that throttle response, wow, so much fun.
 

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That's the thing with the 5-spd and 8-spd...when you go tweaking the axle ratio, you got to examine how it affects 1st gear above all (rather than all of the gears, globally), because 1st gear is skewed out from the rest of the gears the way it is. If you pick an axle ratio that seems good for the track-running gears (2nd/3rd/4th, as the case may be), it pretty much puts the 1st gear way out into no man's land. Essentially, the "short axle" effect is already baked into 1st gear, to take care of getting out of the hole. So if you put an actual short axle on it, then the behavior of 1st gear is like "double-short".
 

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2013 SRT8 Dodge Challenger gear swap from 3.06 to 3.92

Just did swap, car is 5 speed auto, best time before swap was 12.93 @ 112, will be hitting track within a couple weeks to see difference, feels like old street racer I had back in the 80's, totally enjoy cruising much better with the swap, new tune is required, other than that straight forward swap.
 

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2013 SRT8 Dodge Challenger gear swap from 3.06 to 3.92

Just did swap, car is 5 speed auto, best time before swap was 12.93 @ 112, will be hitting track within a couple weeks to see difference, feels like old street racer I had back in the 80's, totally enjoy cruising much better with the swap, new tune is required, other than that straight forward swap.
Can you describe specifically what you changed / mean by 'new tune required'? Thanks.
 
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