321 rear end
Thread Starter
|
Registered User
Joined: Dec 2008
Posts: 4
Likes: 0
321 rear end
Looking at either a 1500 sport or big horn 2016. Lots of good rebates out there.
Anything I like has the 321 rear end and as my 2009 has a 355 and when I'm fully loaded and towing 3000lb loaded boat it's good most of the time.
I'm wondering if anyone has one with the 321 rear end and how much you have towed. Or should try for the 392 rear end as those are the only two choices I have
John
Anything I like has the 321 rear end and as my 2009 has a 355 and when I'm fully loaded and towing 3000lb loaded boat it's good most of the time.
I'm wondering if anyone has one with the 321 rear end and how much you have towed. Or should try for the 392 rear end as those are the only two choices I have
John
Record Breaker
Joined: Jan 2010
Posts: 1,400
Likes: 5
From: San Pedro, California
The 3.21 is fine for what you are towing when mated to the 8 speed. It will be a better towing machine then your 2009 with the 3.55.
Here is why. Your 2009 with the 545RFE has the following ratios: 1=3.00, 2=1.67, 3=1.5, 4=1.00, 5=0.75 and 6=0.67. The 8 speed is, 1=4.70, 2=3.13, 3=2.10, 4=1.67, 5=1.29, 6=1.00, 7=0.84 and 8=0.67.
Multiply your 6 speed ratios by 3.55 and you get the following effective ratios.
1=10.65, 2=5.93, 3=5.32, 4=3.55, 5=2.66 and 6= 2.38.
Now compare the 3.21 with the 8 speed, and you get the following ratios.
1=15.9, 2=10.05, 3=6.74, 4=5.36, 5=4.14, 6=3.21, 7=2.7 and 8=2.15
Compare the two and you see that the 8 speed with the 3.21 is better than the 3.55 with the 6 speed.
So for taking off, you have 15.9 vs 10.65. For cruising you have closer ratios for better managing your rpms.
Of course, if you want to tow heavy, the 3.92 is the way to go. I think that the new rams with the 3.21 with the 8 speed have higher tow ratings than you 2009.
Here is why. Your 2009 with the 545RFE has the following ratios: 1=3.00, 2=1.67, 3=1.5, 4=1.00, 5=0.75 and 6=0.67. The 8 speed is, 1=4.70, 2=3.13, 3=2.10, 4=1.67, 5=1.29, 6=1.00, 7=0.84 and 8=0.67.
Multiply your 6 speed ratios by 3.55 and you get the following effective ratios.
1=10.65, 2=5.93, 3=5.32, 4=3.55, 5=2.66 and 6= 2.38.
Now compare the 3.21 with the 8 speed, and you get the following ratios.
1=15.9, 2=10.05, 3=6.74, 4=5.36, 5=4.14, 6=3.21, 7=2.7 and 8=2.15
Compare the two and you see that the 8 speed with the 3.21 is better than the 3.55 with the 6 speed.
So for taking off, you have 15.9 vs 10.65. For cruising you have closer ratios for better managing your rpms.
Of course, if you want to tow heavy, the 3.92 is the way to go. I think that the new rams with the 3.21 with the 8 speed have higher tow ratings than you 2009.
Last edited by Pedro Dog; Jun 14, 2016 at 07:15 PM.
Rookie
Joined: Jul 2014
Posts: 87
Likes: 0
From: Midwest
The 3.21 is fine for what you are towing when mated to the 8 speed. It will be a better towing machine then your 2009 with the 3.55.
Here is why. Your 2009 with the 545RFE has the following ratios: 1=3.00, 2=1.67, 3=1.5, 4=1.00, 5=0.75 and 6=0.67. The 8 speed is, 1=4.70, 2=3.13, 3=2.10, 4=1.67, 5=1.29, 6=1.00, 7=0.84 and 8=0.67.
Multiply your 6 speed ratios by 3.55 and you get the following effective ratios.
1=10.65, 2=5.93, 3=5.32, 4=3.55, 5=2.66 and 6= 2.38.
Now compare the 3.21 with the 8 speed, and you get the following ratios.
1=15.9, 2=10.05, 3=6.74, 4=5.36, 5=4.14, 6=3.21, 7=2.7 and 8=2.15
Compare the two and you see that the 8 speed with the 3.21 is better than the 3.55 with the 6 speed.
So for taking off, you have 15.9 vs 10.65. For cruising you have closer ratios for better managing your rpms.
Of course, if you want to tow heavy, the 3.92 is the way to go. I think that the new rams with the 3.21 with the 8 speed have higher tow ratings than you 2009.
Here is why. Your 2009 with the 545RFE has the following ratios: 1=3.00, 2=1.67, 3=1.5, 4=1.00, 5=0.75 and 6=0.67. The 8 speed is, 1=4.70, 2=3.13, 3=2.10, 4=1.67, 5=1.29, 6=1.00, 7=0.84 and 8=0.67.
Multiply your 6 speed ratios by 3.55 and you get the following effective ratios.
1=10.65, 2=5.93, 3=5.32, 4=3.55, 5=2.66 and 6= 2.38.
Now compare the 3.21 with the 8 speed, and you get the following ratios.
1=15.9, 2=10.05, 3=6.74, 4=5.36, 5=4.14, 6=3.21, 7=2.7 and 8=2.15
Compare the two and you see that the 8 speed with the 3.21 is better than the 3.55 with the 6 speed.
So for taking off, you have 15.9 vs 10.65. For cruising you have closer ratios for better managing your rpms.
Of course, if you want to tow heavy, the 3.92 is the way to go. I think that the new rams with the 3.21 with the 8 speed have higher tow ratings than you 2009.
Thanks Dog. That is some good information. When towing heavy with the 3:55 diff. gears it is best to have the transmission selector in 4th gear because 4=1.00 (direct drive) is 60ish mph and 2,000+ RPM's.
Can anyone with the 8 speed and 3:21 gears enlighten us as to what transmission gear you select while towing heavy and what speed/engine RPM you like to run? -- Speculation: gear 6=1.00 (direct drive) at 70ish mph and 2,000+ RPM's.
maybe someone with the 3:92's can also chime in? -- Speculation: gear 7=0.84 (overdrive) this could be bad for the transmission.
Last edited by biggcrisp; Jun 16, 2016 at 04:42 PM.
Thread Starter
|
Registered User
Joined: Dec 2008
Posts: 4
Likes: 0
The 3.21 is fine for what you are towing when mated to the 8 speed. It will be a better towing machine then your 2009 with the 3.55.
Here is why. Your 2009 with the 545RFE has the following ratios: 1=3.00, 2=1.67, 3=1.5, 4=1.00, 5=0.75 and 6=0.67. The 8 speed is, 1=4.70, 2=3.13, 3=2.10, 4=1.67, 5=1.29, 6=1.00, 7=0.84 and 8=0.67.
Multiply your 6 speed ratios by 3.55 and you get the following effective ratios.
1=10.65, 2=5.93, 3=5.32, 4=3.55, 5=2.66 and 6= 2.38.
Now compare the 3.21 with the 8 speed, and you get the following ratios.
1=15.9, 2=10.05, 3=6.74, 4=5.36, 5=4.14, 6=3.21, 7=2.7 and 8=2.15
Compare the two and you see that the 8 speed with the 3.21 is better than the 3.55 with the 6 speed.
So for taking off, you have 15.9 vs 10.65. For cruising you have closer ratios for better managing your rpms.
Of course, if you want to tow heavy, the 3.92 is the way to go. I think that the new rams with the 3.21 with the 8 speed have higher tow ratings than you 2009.
Here is why. Your 2009 with the 545RFE has the following ratios: 1=3.00, 2=1.67, 3=1.5, 4=1.00, 5=0.75 and 6=0.67. The 8 speed is, 1=4.70, 2=3.13, 3=2.10, 4=1.67, 5=1.29, 6=1.00, 7=0.84 and 8=0.67.
Multiply your 6 speed ratios by 3.55 and you get the following effective ratios.
1=10.65, 2=5.93, 3=5.32, 4=3.55, 5=2.66 and 6= 2.38.
Now compare the 3.21 with the 8 speed, and you get the following ratios.
1=15.9, 2=10.05, 3=6.74, 4=5.36, 5=4.14, 6=3.21, 7=2.7 and 8=2.15
Compare the two and you see that the 8 speed with the 3.21 is better than the 3.55 with the 6 speed.
So for taking off, you have 15.9 vs 10.65. For cruising you have closer ratios for better managing your rpms.
Of course, if you want to tow heavy, the 3.92 is the way to go. I think that the new rams with the 3.21 with the 8 speed have higher tow ratings than you 2009.
John
Professional
Joined: Dec 2010
Posts: 116
Likes: 0
I tow a 6k pound Camper pretty often with mine. I have the 8 speed with 3.21 gears. I keep it in drive with tow haul turned on and with the cruise set at 70, it generally turns 3100 rpm. It's about 1200 rpm higher than my 2011 with the 5 speed trans would spin, and the new one gets about 10% less mileage too. Although with the 8 speed, I barely even notice the weight behind me, whereas with the old truck it was pretty sluggish trying to accelerate.