Diff Ratio Dilema

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jasonlas

jasonlas

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Gday guys/gals.

In the AP6 Wagon im building im running the 5.7 hemi & the 5speed auto from a Dodge Ram.
Im wondering what the standard Ram diff ratiso are, what the standard 300C ratios are (if different) & if anyone has changed ratios & found success?
Cheers
 
I've read that Rams have 3.55 gears and the 300C runs a 3.06.
I'm running 3.45 in my car with a Supra 5-spd but I don't have the Hemi installed yet.
I have a 2004 Ram 5.7.
 
Do you want good gas mileage or great mileage? I first had 2:73 and got 27mpg then I had 3:23 had 24 now I have 3:73 and run like a bat outa hell and love it. and don't even care what my mpg is. It basically depends on what you wanna do with it I know I wasn't any help sorry.
 
Tire size plays into it as well as it changes the overall drive ratio. A truck with tall tires can get away with a higher gear ratio compared to a car as they work out to be fairly equivalent when you combine the tire size and gear ratio. I'm running a 3.55 setup with my fairly small factory-ish size tires. I put in a T56 with a 0.5:1 overdrive though to keep the revs down. I imagine your 5 speed is probably ~0.7:1 overdrive? That would be like my 5th gear and I cruise around 2000 rpm at 70 if that helps.

If you plan to do a lot of highway miles anything on the lower side of 3-3.5:1 would probably be a pretty good fit. If you want more fun and punch then 3.5-4:1 would likely be the way to go.
 
Cheers guys,

3.55 is what i thought was the standard Ram diff ratio.
This is the answer i needed as i will stick to this as ive heard the trans can have possible shift point issues if changed.
The engine etc is in an AP6 wagon which is probably half the weight of a Ram so the thing should boogie!
Cheers all for the feedback.
 
I also have a 2004 Hemi but have the 545rfe trams I was really happy with 3:23 for highway cruiseing and great on hill climbs and I have never hooked upped the overdrive switch yet. Which I think I will do to see how it does good luck. My 3:73 gears are from a Ford Explorer 8.8 rear end I'm using the 3:23 were from a 8 3/4
 
Spoke to somebody years ago with a supercharged 300C SRT8, he changed the factory 3.06 gears out for whatever was available for the Challenger at the time, something around 3.5 I think and he reckoned it was the best bang for buck he had got out of the car. Just remember that the SRT8 300 runs 20" wheels, which will be a bit taller than your regular Valiant wheels.
 
Go with 3.91's and a 28 inch tall tire. Here's why.....the rfe545 has a 3.001 first gear, and outta the hole you move the car like a scalded cat on a hot tin roof, and with 4th and 5th being overdrive (5th is .67 is memory is correct) with a 28 inch tall tire and the 3.91's you'll be turning 2kish at 70mph. Now I'm going off memory when I did this swap in a 64 Polara 500 so I could be off a tad.
 
5.7 hemi said:
Go with 3.91's and a 28 inch tall tire. Here's why.....the rfe545 has a 3.001 first gear, and outta the hole you move the car like a scalded cat on a hot tin roof, and with 4th and 5th being overdrive (5th is .67 is memory is correct) with a 28 inch tall tire and the 3.91's you'll be turning 2kish at 70mph. Now I'm going off memory when I did this swap in a 64 Polara 500 so I could be off a tad.
Click to expand...
my ram has a 3:90 , w/ 20" tires. jfyi
 
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