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Discussion Starter · #1 ·
Having a hard time finding out what are the factory gears our cars come with? I have a 2006 srt8 300. At 70 Im turning about 2200 rpms.

Thanks,
Jeff
 

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Discussion Starter · #4 ·
Alright cool thanks guys, Has anyone ever done a rear end gear swap if so what were the gears yall went with? I thought about maybe a 355 or 390 if they offered that?
 

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I'm guessing you don't want to do much Highway driving?
 

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Discussion Starter · #6 ·
Not really I do about 10 miles a day. Im hopen at income tax time I can do a set of ported heads,cam,ported intake and tb with a stall and maybe a set of gears but well see.
 

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Watch you don't go too short on the rear gear with H/C and a stall or else you will never launch on streets... Just with the 3.06 and a 2800 with heads and cam in a 5.7 its a chore! The stall converter made her really light on her feet. You may want to look at beefing axles before going a lower gear as well, with heads and cam and a stall your looking to snap one unless you upgrade... Go to a shorter gear and grab traction and you will spit a shaft for sure! :)

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I went from 3.06 to 3.55 and couldn't be happier. You can get 3.73, 3.92, and 4.10's as well. Upgrade yours to a getrag unit and upgraded clutches. The newer axles with the getrag should be able to handle the heads/cam.
 

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I'd recommend a 3.55 as a good all around upgrade for street driving plus highway cruising. Any higher than that and highway cruising may prove to be noisy and expensive.
 

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I'd recommend a 3.55 as a good all around upgrade for street driving plus highway cruising. Any higher than that and highway cruising may prove to be noisy and expensive.
I agree....I had 3.73's in my Jeep and it got annoying at 80mph.
 

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Discussion Starter · #12 ·
How much does it cost to upgrade a rear end? And what kind of power gain would I be looking at with a ported set of heads, cam and intake with throttle body? I already have headers and a cat back. Thanks for every ones input
 

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I think Erik at BFNY recently had a deal going on for that swap. Might want to check with them.
 
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How much does it cost to upgrade a rear end? And what kind of power gain would I be looking at with a ported set of heads, cam and intake with throttle body? I already have headers and a cat back. Thanks for every ones input
I bought a complete 25k miles 3.91 2010 Challenger LSD Getrag diff 225 axles hubs rear shaft coupler bolts everything needed for the swap for $1200

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I agree....I had 3.73's in my Jeep and it got annoying at 80mph.
Did you have an SRT8 Jeep? They all come with 3.73's, but not sure why yours was annoying at 80 MPH. Mine loves 80...
 

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My 2006 Jeep GC Limited with a 4.7 had 3.73 in it and I frequently cruised at 70-80 with no problem. Never felt like it was struggling or anything. I replaced the 2.73 in a 2004 Crown Vic with 3.55 posi and it was a different beast with a SCT tuner.
 

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I can tell ya right now that unless this lives at the track and takes back roads to it and doesn't ever need to worry about highway fuel economy I would not do 3.73 or shorter gear... A 3.55 will wake her up just fine. While many I'm sure will argue and say 'I have 3.73's' I just don't know why a street driven hemi with a nag 1 transmission that has virtually no 1st gear with 3.73's requires it. On regular street tires my friends Charger SBee was no faster with them than his 3.55's as he never had traction, at the track it dropped a 10th or two... He went through 3 different ratios and I will have to ask him but I think he settled on 3.23's as he needed some highway gear as well. Personally thrumming around at 3k or more on the highway at 70 sucks! If I want to go 11's there are a lot better ways of getting there imo... Plenty of stock geared cars running low 11s... Even my 5.7 with a 3.06, 2800 stall and heads and cam imo is a pita to launch on the street with good street tires... I'm looking into drag radials. A stall converter changes the world of torque! I personally would advise one ahead of a diff, see how it responds then, determine if you have any flat spots and adjust your gear for it. To me add the power, help it get through the transmission with a T/C and then pick what gears you need to put it to the road...

But once again... Just opinion!

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Did you have an SRT8 Jeep? They all come with 3.73's, but not sure why yours was annoying at 80 MPH. Mine loves 80...
It was an SRT and just listening to the engine at 3k got a little annoying. I know, I know, go faster...but it wasn't an option at the time. :)
 

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I can tell ya right now that unless this lives at the track and takes back roads to it and doesn't ever need to worry about highway fuel economy I would not do 3.73 or shorter gear... A 3.55 will wake her up just fine. While many I'm sure will argue and say 'I have 3.73's' I just don't know why a street driven hemi with a nag 1 transmission that has virtually no 1st gear with 3.73's requires it. On regular street tires my friends Charger SBee was no faster with them than his 3.55's as he never had traction, at the track it dropped a 10th or two... He went through 3 different ratios and I will have to ask him but I think he settled on 3.23's as he needed some highway gear as well. Personally thrumming around at 3k or more on the highway at 70 sucks! If I want to go 11's there are a lot better ways of getting there imo... Plenty of stock geared cars running low 11s... Even my 5.7 with a 3.06, 2800 stall and heads and cam imo is a pita to launch on the street with good street tires... I'm looking into drag radials. A stall converter changes the world of torque! I personally would advise one ahead of a diff, see how it responds then, determine if you have any flat spots and adjust your gear for it. To me add the power, help it get through the transmission with a T/C and then pick what gears you need to put it to the road...


But once again... Just opinion!

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Not sure i could sum it up any better........although I haven't played with gears on my SRT's, I did lots of gear changes on my LS1 that I raced. Steeper gears can be a PITA, and as said above, are part of a lot of many moving parts in the quest to go faster. I got my LS1 in the 10's with 3.73's as part of a complete rear end swap (Strange 12 bolt) but they were not ideal for the street at all.

Another word of advice.......if you are doing just gears and not swapping out the whole rear, be very careful who you get to do it. I have seen MANY gear swaps that resulted in significant gear whine due to incorrect installations. Getting gears right takes a mechanic that has done it a lot.
 
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At the strip the geared cars are no faster unless they can hook it up. Our trans has a very low first gear (3.59), not at all like many other 4 speed units (2.48 in my 4L80E). This makes 1st a 10-1 multiplication!

What that means is you already over powered your tires before you even got off the line.

BUT a shorter gear will make the car feel all perky on the street. The trade is revs on the highway.

You don't have to learn how to launch the car with stock gearing, but if you did you may realize that shorter gearing is a trade off...
 
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