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Old 01-22-2018, 02:25 PM   #1
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Rear Gear Ratio & RPM's

I have a RAM 1500 with a 5.7 hemi, 8 speed and 3.55 rear.

At 60 MPH on level ground the RPM's are about 1500. If I had the same engine with the same transmission how much higher would the RPM's be with a 3.92 rear?

Is this difficult to calculate?

Thanks!
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Old 01-22-2018, 02:41 PM   #2
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The ratio of the two rear ends, multiplied by the original engine speed, gives 1656 rpm. (3.92/3.55)*1500
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Old 01-22-2018, 04:13 PM   #3
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Is it really that simple?
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Old 01-22-2018, 08:30 PM   #4
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Is it really that simple?


Yep. A higher ratio means higher RPM for the same speed, but more torque as well.

So the simplest answer to your question is to compare the two ratios.
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Old 01-23-2018, 11:10 AM   #5
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Hi there, on a different note, I have an 08' ram hemi, 5 speed trans with a 3.92 rearend averaging 13 MPG pulling a 25' AS in and around the high desert. Thinking about upgrading to a new dodge with the 8 speed trans, hemi. Not sure to stay with the 3.92 or going with the 3.55. What average mileage are you currently getting?

Thanks

Lynn
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Old 01-23-2018, 11:33 AM   #6
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A ratio question ... if towing with Ford’s 10-speed automatic transmission, is careful selection of the rear-end ratio important?

With 10 gears to choose from, it might be easy to work out an effective final drive ratio, no matter what’s spinning in the rear end.
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Old 01-23-2018, 11:45 AM   #7
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Originally Posted by aliner View Post
Hi there, on a different note, I have an 08' ram hemi, 5 speed trans with a 3.92 rearend averaging 13 MPG pulling a 25' AS in and around the high desert. Thinking about upgrading to a new dodge with the 8 speed trans, hemi. Not sure to stay with the 3.92 or going with the 3.55. What average mileage are you currently getting?

Thanks

Lynn
I currently am pulling a 25' AS with my RAM 1500. I have the 3.55 and am thinking of going to 3.92. That's why I asked the question about RPM's. I currently average 11.5-12.5. Now that includes hilly country (not mountains but what is common in the east). When running on level ground I can average 13.0.

The 2019 RAM 1500 has new tow package that specs a 3.92 rear. It's too early to get a MPG rating but they expect it to be better. The tow package also includes the new e-torque hybrid system.
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Old 01-23-2018, 03:01 PM   #8
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I would wait for the 2019 Ram
It will have 2500 lb load capacity and 12,700 towing with the hemi
They are trying to bridge the gap between 1500's and 2500's
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Old 01-23-2018, 04:23 PM   #9
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You must have skipped basic math in grade school!!
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Old 01-23-2018, 05:43 PM   #10
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That new Ram will be interesting to see how it specs out. Any idea when it is supposed to be in production?
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Old 01-23-2018, 05:50 PM   #11
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That new Ram will be interesting to see how it specs out. Any idea when it is supposed to be in production?


It just so happens that I stopped at a dealership today and asked that same question. I was told that limited production has already started. The salesman said they expect to have a few by the end of Feb. Of course this is a salesman talking!
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Old 01-23-2018, 05:53 PM   #12
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You must have skipped basic math in grade school!!


I skipped a lot of things in grade school! Thanks for pointing out one of them!
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Old 01-23-2018, 09:42 PM   #13
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It just so happens that I stopped at a dealership today and asked that same question. I was told that limited production has already started. The salesman said they expect to have a few by the end of Feb. Of course this is a salesman talking!
There you go. I have a 2017 Ford Ecoboost so I won’t be ready for a pickup for at least 2 or 3 years. That will give plenty of time to see if this new RAM has some significant bugs and what people think about it as a TV.
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