2008 short bed single cab with 2015 longhorn wheels.

[nathantc]

Bought it 9-16-2020, already ordered new OEM headlights and grille. Today i picked up some 2015 longhorn edition 20s. they look like they belong there.

anyway im happy with the lil 3.7 v6 but i feel 3.55 gear is to tall for the lil guy. any head wind or overpass and it has to kick out of overdrive just to maintain. one person told me 4.56 will get me right at 2100 rpm at 60mph with stock tires. can anyone here confirm this. i know there is not a lot of difference between 3.55 and 3.92 but im leaning towards just swapping the entire rear axle to a 3.92 as its ez to find in a salvage yard. 4.56 is more pricey and well. honestly i feel it would be to low.

i'm also thinking of a 4th gen jump seat. prefer the 3 cup holders on it to the pull out dash one. would like to just never need the pull out dash one.

any insight would be appreciated, but please no hate for the lil 3.7. i know it's the underdog and i have no intention of "hoping it up" it's just a parts getter and daily run around truck for when im not in the freightliner. if i ever need to tow anything. i clearly have a bigger truck lol

 

[Badger 13]

Can't help on what your looking for, but you do have a nice looking truck.

 

[HemiLonestar]

What trans do you have? 42RLE or 545RFE?

 

[Daw14]

Go to “4-lo” for gear ratio chart

 

[nathantc]

sorry not getting email notifications for some reason. anyway i think it should be the 42RLE as i'm pretty sure that comes standard in the 3.7 V6 trucks. should be the exact same overdrive ratio of .69 though.

much needed new headlights, grille on the way.

 

[nathantc]

oh and im also wanting to lower the rear to level it. i doubt the 1.5" that shackles will give will be enough. has anyone ever done a shackle flip or used the 3" drop springs. i dont want to modify the front at all if possible.

 

[Fishstickz]

Nice lookin' truck! As you've already found out, yeah the 3.7 is underpowered in a full-sized truck lol

Idk how bad your truck is with the downshifting but I know mine's pretty dang bad. My calculated engine load is always over 80% and stays at 90-100 even on the flatter highways. I never get over 15 MPG, which is mostly because I'm in 3rd gear for half of my highway miles

If you think 4.56s is too low, the 4.10s are a pretty decent middle ground. I'm gonna see how the V6 reacts to 33s before I decide on which ratio to swap to. But since gear swaps are so pricey, I can't blame ya for looking at full axle swaps. 3.92's will help you out a bit

As for the 4th gen jumpseat, DO IT! It was by far my favorite mod to this truck. I can't explain how much happier I am with that 4th gen jumpseat, plus people will think you're truck is weird having 5 cupholders in a single cab. If you're feeling extra, swap in 4th gen seats with it. I had those same cloth seats as you do before I swapped in some 2017 sport seats from a fellow forumer. They're sooo much better in every way



By the way, if you don't have self control these guys can and will spend your money lol

 

[nathantc]

did the seats bolt directly in. im honestly thinking of doing exactly what you did there. swapping the seats, all 3, from a 4th gen. my seats are fine but i like the look of the 4th gen and the comfort of them better. more adjustability.

that said my truck cannot stay in overdrive at 65mph if there is any head wind, or even a overpass. i have 355s now, and 275/60/20s which is a 33" tires, no difference from the 285/70/17s i removed from the truck. only about 1/2" shorter. speedo will need to be recalibrated for the 275/60/20s as that is the size i want to run with. at 65mph im actually doing 67mph.

what gear and tire size are you currently running

 

[nathantc]

according for "4-lo" the calculator on there i should actually have a 3.27 ratio not a 3.55 so either i have a very very tall gear for a v6 or that thing is a bit off.

currently in my truck at 80mph with a 33" tire in overdrive at right at 2k rpm.

 

[Fishstickz]

did the seats bolt directly in. im honestly thinking of doing exactly what you did there. swapping the seats, all 3, from a 4th gen. my seats are fine but i like the look of the 4th gen and the comfort of them better. more adjustability.

that said my truck cannot stay in overdrive at 65mph if there is any head wind, or even a overpass. i have 355s now, and 275/60/20s which is a 33" tires, no difference from the 285/70/17s i removed from the truck. only about 1/2" shorter. speedo will need to be recalibrated for the 275/60/20s as that is the size i want to run with. at 65mph im actually doing 67mph.

what gear and tire size are you currently running

Everything is bolt-in except the jumpseat. The left side of the jumpseat is bolted into the passenger seat, so no problems there. But on the drivers side, the jumpseat is supposed to bolt into the cab, but 3rd gens don’t have those bolt holes or mounts. A lot of us just leave that side unbolted and don’t have any issues, but a couple of people fabbed up some custom brackets for peace of mind. My seats have been in for a good while now and I’m not worried one bit.

Overall its basically a bolt-in swap, but the electrical will require some custom wiring if you get powered seats, but not bad at all. Pretty sure you could even swap in some 5th gen HD seats if you want the modern 2020 styling, just make sure they’re out of a 2500 or 3500.

I have the same problem as you with headwind, and I’m just running 265/70r17s which are a bit smaller at 31.6 inches. I’m on another gear ratio calculator and with 4.56s and your 33s, you’d be at 2083 RPM at 65 according to the calculator I use. I’ve found it to be quite accurate.

Roughly, it looks like 4.10s would raise your RPM 250 or so across the board, while 4.56s would raise it by 500. Of course thats a VERY rough way of looking at it lol

www.grimmjeeper.com/gears.html


Sent from my iPhone using Tapatalk

 

[nathantc]

yeah no sticker in glove box, or tag on axle, guess i'll have to find out the hard way and get under the truck to find the ratio for sure. anyway i normally use this one https://www.tremec.com/calculadora.php and it shows with a a 4th gear of .69, final drive of 3.55, tire size of 33", and engine rpm of 2000. the speed is 80 mph which is spot on for my truck. yet the one on 4-lo says it would be a 3.27 lol. im betting its a 3.55. i highly doubt an 08 with a v6 came with anything taller than a 3.55 and honestly that is to tall for it.

3.55 at 65mph shows 1622 rpm at 75mph 1872 rpm (like my truck currently)
3.92 at 65mph shows 1791 rpm at 75mph 2069 rpm
4.10 at 65mph shows 1873 rpm at 75mph 2162 rpm
4.56 at 65mph shows 2084 rpm at 75mph 2410 rpm

with these numbers its a hard choice. 2000 rpm at cruise speed was the best for towing and mpg with my cummins. im not sure what would be best for this engine. i would think it would be about the same. i have to keep reminding myself it's a higher revving engine and makes torque and power higher up in the rpm range so 4.56 seems to low but may be just right for this engine as far as mpg and drivability go. idk. but seeing these numbers i feel it would be pointless to go to a 3.92 from a 3.55 unless done 100% free.

as for the seats, thanks man great info. 4th gen seats are for sure in the future plans. as for the jump seat im sure i can figure that one out. just wanted to be sure the driver and passenger seats bolt down correctly.

 

[Fishstickz]

yeah no sticker in glove box, or tag on axle, guess i'll have to find out the hard way and get under the truck to find the ratio for sure. anyway i normally use this one https://www.tremec.com/calculadora.php and it shows with a a 4th gear of .69, final drive of 3.55, tire size of 33", and engine rpm of 2000. the speed is 80 mph which is spot on for my truck. yet the one on 4-lo says it would be a 3.27 lol. im betting its a 3.55. i highly doubt an 08 with a v6 came with anything taller than a 3.55 and honestly that is to tall for it.

3.55 at 65mph shows 1622 rpm at 75mph 1872 rpm (like my truck currently)
3.92 at 65mph shows 1791 rpm at 75mph 2069 rpm
4.10 at 65mph shows 1873 rpm at 75mph 2162 rpm
4.56 at 65mph shows 2084 rpm at 75mph 2410 rpm

with these numbers its a hard choice. 2000 rpm at cruise speed was the best for towing and mpg with my cummins. im not sure what would be best for this engine. i would think it would be about the same. i have to keep reminding myself it's a higher revving engine and makes torque and power higher up in the rpm range so 4.56 seems to low but may be just right for this engine as far as mpg and drivability go. idk. but seeing these numbers i feel it would be pointless to go to a 3.92 from a 3.55 unless done 100% free.

as for the seats, thanks man great info. 4th gen seats are for sure in the future plans. as for the jump seat im sure i can figure that one out. just wanted to be sure the driver and passenger seats bolt down correctly.

Theres a website that can pull up your build sheet and will list all your options including gear ratio. I’ll try to find a link for it

As far as I know every 3.7-42RLE combo came with 3.55s (and possibly optioned with 3.92s? Not sure on that), and the 3.7-manual could come with 3.21s or maybe 3.55s. There is one guy on here thats running his 3.7 with like a 6 inch lift and 35s, and he swapped to 3.92s. I haven’t heard from him in a bit tho

I think cruising about 2000 would be the best. Usually I’d say lower cruise RPM is better for MPG, but thats with bigger engines that don’t have to downshift when a bug hits the windshield lol. I’ve been leaning towards 4.56s lately simply because of the low end torque to get these things moving and stay moving. Plus it’ll help with towing and dealing with days of high speed headwinds

And yeah both seats match up perfectly. I wired up power to the 12v in the center console and to the drivers seat for the seat movement and thats all I wanted lol


Sent from my iPhone using Tapatalk

 

[nathantc]

im for sure doing the seats.
as for gears ive talked myself into the 4.56 ill be doing that when funds allow. i usually only cruise at 65mph anyway but could still do 75 mph no problem. i honestly think with 33s the 4.56 might be just right as far as driveability goes. that said 300 miles of all interstate and i was about 15.5 mph so that sux. half of that was with the OD off. every time it would shift ot OD the truck would start to slow down till it down shifted. so i just turned it off. seems tow/haul does nothing. i always thought it just turned OD off lol. 4.56 gears in OD are a lot less RPM than 3.55 gears in 3rd. so it should work out.

 

[Fishstickz]

im for sure doing the seats.
as for gears ive talked myself into the 4.56 ill be doing that when funds allow. i usually only cruise at 65mph anyway but could still do 75 mph no problem. i honestly think with 33s the 4.56 might be just right as far as driveability goes. that said 300 miles of all interstate and i was about 15.5 mph so that sux. half of that was with the OD off. every time it would shift ot OD the truck would start to slow down till it down shifted. so i just turned it off. seems tow/haul does nothing. i always thought it just turned OD off lol. 4.56 gears in OD are a lot less RPM than 3.55 gears in 3rd. so it should work out.

Yeah I consistently get 15-15.5 each fillup so I feel the pain lol

My only concern with 4.56s is driving 80-85 on the interstates, I don’t know how much I like the engine being wound up so high with the 4.56s for a long period of time. But like you said 4.56s in OD is less than 3.55s in 3rd, so that kinda helps the thought process. Besides, if I decide the RPM is too high with 4.56s and 33s, I’ll have a dang good excuse to buy some 35s lol

On the bright side, 4.56s will probably be easier on just about everything in the drivetrain. Engine won’t bog down, tranny won’t have to shift in and out of OD as much, torque converter can run unlocked more often, etc.



Sent from my iPhone using Tapatalk

 

[nathantc]

Yeah I consistently get 15-15.5 each fillup so I feel the pain lol

My only concern with 4.56s is driving 80-85 on the interstates, I don’t know how much I like the engine being wound up so high with the 4.56s for a long period of time. But like you said 4.56s in OD is less than 3.55s in 3rd, so that kinda helps the thought process. Besides, if I decide the RPM is too high with 4.56s and 33s, I’ll have a dang good excuse to buy some 35s lol

On the bright side, 4.56s will probably be easier on just about everything in the drivetrain. Engine won’t bog down, tranny won’t have to shift in and out of OD as much, torque converter can run unlocked more often, etc.



Sent from my iPhone using Tapatalk

65mph is the max speed limit for most everything around me, other than that ill see 75 from time to time. also the rpms wont be to bad in OD like stated and being as i never have a need at all to ever tow anything it should never need to kick out of OD at hwy speeds.. i got this truck to only be a daily driver, run and get oil and parts. hit a drive thru and what not. if i ever need to tow anything i have a truck for that. lol
the only time it should ever leave OD is if you mash on it or pulling more than the lil v6 should be pulling. not really sure why Dodge specced it with such a tall gear for such a weak power plant. eiter way im happy with the truck overall. i just wanted a nice looking run around truck. being as im 6'5" me and cars dont get along, and if you have ever had a 5 gallon bucket of oil leak in a carpeted suv, you would know why that was not an option for me.

 

[WhiteExpress]

4.56 gears and 33" tires is a nice match. I put 4.56 gears in my '00 with 34" tires and I really wish I'd gone 4.88s. I'll say this, with better gears, it made the truck so much more enjoyable to drive, like amazingly so. (D O I T!)

The 3.7 is going to do better with some RPMs. The engine kind of 'free wheeling' at a higher RPM vs loaded down at a lower RPM will get better MPG too.

Your RPMs aren't ever going to be mathematically correct thanks to your torque converter, don't worry about it, just understand it's going to be pretty close to what's calculated.

 

[nathantc]

4.56 gears and 33" tires is a nice match. I put 4.56 gears in my '00 with 34" tires and I really wish I'd gone 4.88s. I'll say this, with better gears, it made the truck so much more enjoyable to drive, like amazingly so. (D O I T!)

The 3.7 is going to do better with some RPMs. The engine kind of 'free wheeling' at a higher RPM vs loaded down at a lower RPM will get better MPG too.

Your RPMs aren't ever going to be mathematically correct thanks to your torque converter, don't worry about it, just understand it's going to be pretty close to what's calculated.

my thoughts exactly. and i figure at cruise speed, flat ground, normal conditions there is about 100 rpm parasitic loss due to converter. its more drastic with the converter unlocked under heavy load.