3.92 with 5-speed vs. 3.21 with 8-speed

[Trexterra]

I never drove a 5 speed but I noticed a pretty decent change swapping from 3.21 to 3.92 with my 8 speed. 3.21 felt perfectly fine but I wanted lower gears for towing. Well worth it.

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[shane1981]

also if i were going of the dash reading my truck with 3.92 gets about 5 more miles to the gallon.

tuned by jay greene

 

[Mineralram]

my 2013 was a 6 speed with 3:92's and my brother had a 2014 with 8 speed 3:21 and was able to catch up without an issue. I have since traded the 2013 for a 2015 and 2017 with 3:21 and 8 speed and find really no difference in gas mileage or performance and i towed my 7500 lbs travel trailer 28ft with no problems on both gear ratios

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[RLJ10X]

I wonder why they dropped the 3.55 when they came out with the 8 speed? That ratio seems like it would be a good compromise between the 3.21 and the 3.92.

I have a tuned 5/6 speed with 4.10s. I test drove an untuned 8/3.21. ****, may be a bit harsh. But I was not impressed. However, Ive seen videos of tuned 8s. Gamechanger.

 

[Robocop_9]

I wonder why they dropped the 3.55 when they came out with the 8 speed? That ratio seems like it would be a good compromise between the 3.21 and the 3.92.

I have a tuned 5/6 speed with 4.10s. I test drove an untuned 8/3.21. ****, may be a bit harsh. But I was not impressed. However, Ive seen videos od tuned 8s. Gamechanger.

I'm running an 8 with 3.21 and bolt ons. Hemifever tuned with 33x12.50 and it's no ****. I could only imagine if I had 392 or 410s.


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[Mineralram]

if you wanna drive a ****, try a ford crap boost or a chubby pick up

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[thekevin]

I just bought a 2017 3.92/8spd this week and coming from a tuned ecoboost I was fairly happy with the low end on it and how it feels under normal driving completely stock. No way it would hang with my ecoboost in a race but maybe after its broken in and tuned it will be a different story.

Now if you want to talk about a ****, I test drove a 2017 GMC and even with 3.42's instead of the 3.08's I felt like I had to put it to the floor to get it moving.

 

[metalmancpa]

I am quite surprised the get up and go of my 2014 Ram 1500 Hemi Crew with the 3.92 / 8-speed Hemi. I came from a Hemi AWD Chrysler 300 and she moved off the line. Although no comparison to the 300 off the line, the Ram does an admirable job going 0-60. It still gets off quick and muscles up to speed.

 

[RLJ10X]

I NEVER buy the "rip-off" extended warranty. Ever.
But if l ever bought something with 2 turbos, l would buy the extended warranty.

And l am sure that by the time you Tuned the Ecoboost, that would void the engine warranty.

 

[hemisport5.7]

I just bought a 2017 3.92/8spd this week and coming from a tuned ecoboost I was fairly happy with the low end on it and how it feels under normal driving completely stock. No way it would hang with my ecoboost in a race but maybe after its broken in and tuned it will be a different story.

Now if you want to talk about a ****, I test drove a 2017 GMC and even with 3.42's instead of the 3.08's I felt like I had to put it to the floor to get it moving.

Glad you came over to the light. All I hear is how much faster a tuned ecoboost is over the hemi. I don't deny it is fast but I'd rather have a sexy sounding V8 over a ricer pickup with farty exhaust and a blow off valve. Lol

 

[thekevin]

When I first started the truck with the sales guy sitting in there with me I smiled and turned to him and told that sounds like a truck.


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[regularcab2500]

I have a little experience with this but my comparisons arent direct so bear with me. My brother has a 15 with 8/3.21 combo and it lights the tires up from a dead stab no problem. My 2500 with a 6.4 a 3.73 would get him off the line but above 60 he had me by nearly a truck length by 100. Now my dads durango is awd with 4.10s and front and rear lsd. That thing hauls ass off the line but gets walked by my brothers truck on the highway, mind you its an 05 magnum hemi with the 5spd. Personally i would never get 3.21s in a new truck but you'll be hard pressed to find one on a dealer lot with 3.92s at least in my area. That said its no slouch though and if my brother had 3.92s i cant imagine how fast he would go through tires (he drives like an idiot). You will be fine with 3.21s and fuel economy will be pretty much the same with any gear. That 4.71 first gear in the 8 speed is rediculous and those trucks would probably light up the tires with a 2.73 or higher rear end.

I have to add that my g37 is significantly faster than all of them

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[BigSloth]

Alright, I'm gonna post some non anecdotal data about the differences. This is info taken straight from any final drive calculator you can find online. A final drive calculator takes into account transmission gearing, rear axle gearing, and tire size to give you what's know as a final drive ratio, or an effective gear ratio.

All data was assumed for stock trucks, a 3.21 8 speed, and a 3.92 5 speed, assuming both are on the stock size 33" tires.

The 8 speed transmission has very low gears in first and second. This is why they can run a higher gear in the rear. Gear ratios are as follows, in order of 1/2/3/4 etc

8HP70: 4.71/3.14/2.10/1.67/1.29/1.00/0.84/0.67
545RFE : 3.00/1.67/1.00/0.75/0.67

With the data from the final drive calculator, we end up with effective gear ratios of:

8HP7015.12/10.08/6.74/5.36/4.14/3.21/2.70/2.15
545RFE: 11.76/6.55/3.92/2.94/2.63

Comparison of the two sets of data shows that the 8 speed truck carries a significant advantage, as it's effective gear ratio in first gear is roughly 25% lower, resulting in better off the line performance, and more torque available for towing. In second gear the 8 speed now is still within 10% of the 5 speed's first gear effective ratio. Shifting again into 3rd gear on the 8 speed, your effective ratio is now nearly equal to 2nd gear on the 5 speed. Even when the 8 speed is in 5th gear, it still has a slight mechanical advantage over the 5 speeds 3rd gear, as the 8 speed is still in an underdrive gear while the 5 speed is in its direct drive.

In terms of hwy fuel economy, he who can move the fastest with the least RPM wins. Though both transmissions have the same final overdrive ratio of 0.67, the 8 speed truck wins because of the higher axle ratio, resulting in the 2.15 ratio compared to the 5 speeds 2.63.

In summary, the 8 speed transmission allows the engine to stay within its peak power and torque, meaning better acceleration and performance, and offers a lower RPM in overdrive.

 

[RLJ10X]

Have you noticed that since the 8 speed has been out, a lot less has been made of doing a manual transmission swap?

I'd love to have the 8, but, its not worth the $20K it would take to get one. Plus, my tuned 545RFE with 4.10s, isn't shabby, either.

 

[BrianandChrissy]

Alright, I'm gonna post some non anecdotal data about the differences. This is info taken straight from any final drive calculator you can find online. A final drive calculator takes into account transmission gearing, rear axle gearing, and tire size to give you what's know as a final drive ratio, or an effective gear ratio.

All data was assumed for stock trucks, a 3.21 8 speed, and a 3.92 5 speed, assuming both are on the stock size 33" tires.

The 8 speed transmission has very low gears in first and second. This is why they can run a higher gear in the rear. Gear ratios are as follows, in order of 1/2/3/4 etc

8HP70: 4.71/3.14/2.10/1.67/1.29/1.00/0.84/0.67
545RFE : 3.00/1.67/1.00/0.75/0.67

With the data from the final drive calculator, we end up with effective gear ratios of:

8HP7015.12/10.08/6.74/5.36/4.14/3.21/2.70/2.15
545RFE: 11.76/6.55/3.92/2.94/2.63

Comparison of the two sets of data shows that the 8 speed truck carries a significant advantage, as it's effective gear ratio in first gear is roughly 25% lower, resulting in better off the line performance, and more torque available for towing. In second gear the 8 speed now is still within 10% of the 5 speed's first gear effective ratio. Shifting again into 3rd gear on the 8 speed, your effective ratio is now nearly equal to 2nd gear on the 5 speed. Even when the 8 speed is in 5th gear, it still has a slight mechanical advantage over the 5 speeds 3rd gear, as the 8 speed is still in an underdrive gear while the 5 speed is in its direct drive.

In terms of hwy fuel economy, he who can move the fastest with the least RPM wins. Though both transmissions have the same final overdrive ratio of 0.67, the 8 speed truck wins because of the higher axle ratio, resulting in the 2.15 ratio compared to the 5 speeds 2.63.

In summary, the 8 speed transmission allows the engine to stay within its peak power and torque, meaning better acceleration and performance, and offers a lower RPM in overdrive.

Well said. You must be an English major? Your format of the write up is flawless. Well done sir.

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[BigSloth]

Well said. You must be an English major? Your format of the write up is flawless. Well done sir.

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Thanks. No English major here, never been to college. I'm a Lexus master tech.

 

[BigSloth]

Have you noticed that since the 8 speed has been out, a lot less has been made of doing a manual transmission swap?

I'd love to have the 8, but, its not worth the $20K it would take to get one. Plus, my tuned 545RFE with 4.10s, isn't shabby, either.

Yes. Manual swaps are losing popularity, mostly because it's just not worth the hassle.

Eh. I used to think the same thing. I had an 06 with a 545rfe with an edge 3400 converter, sharadon built valve body, and hemi fever trans tune, and it doesn't compare to the responsiveness and shift feel of a stock 8 speed. Now that HP tuners has unlocked 8 speed Trans tuning, the 8 speed trucks are about to start widening the performance gap.

 

[RLJ10X]

^Thats true. But there will always be something newer, and better. Keeping up with the Jones's gets real expensive real fast. My plan is to retire with a $ Mil. I will happily sit on the sideline and watch. The fastest truck here, is still a slug compared to my nice old 01 929.

But if my truck was ever stolen, never to be seen again.......

 

[BrianandChrissy]

Thanks. No English major here, never been to college. I'm a Lexus master tech.

Well, you're very well versed, and you should be proud of that. So many people in the world nowadays lack these skills. My kudos to you. Again, well done chief.

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