This MPG is why I bought the 3.21

Daw14 · Jul 15, 2022

Wild one said:
There's a theory floating around,that the trucks actual exhaust system,might be a bigger contributor to manifold bolt breakage,then we think.Example being the 5.7 cars use basically the same cast iron log manifold,but with a set of dual pipes,that lead back to an X farther towards the rear of the car,then the trucks squashed midpipe is,and the cars don't break manifold bolts. The theory does make you wonder if the actual exhaust system on the trucks might be putting more stress on the back manifold bolts,then we think,as it's always the back bolts that break,which is where the exhaust pipes would be exerting the most pressure.You'd think if it was totally heat related and temp changes breaking bolts,the front bolts and middle bolts would be more inclined to break,but i've never seen or heard of a truck actually breaking a front manifold bolt

My theory is the cats are the heat ,thus why it’s always the two rear most that are worst .

Docwagon1776 · Jul 15, 2022

ramffml said:
MDS basically turns off half your engine and stresses the other half (basically 4 cylinders running WOT) but lugging while doing it (low rpms but high load = bad). It shakes sometimes in and out of MDS. I have no facts or data to support this, but I'm convinced it's better for the life of the engine to let it coast around easily with 8 cyliders firing, vs running 4 at pretty high load.

So MDS causes the motor more 'stress' to run the same speed but running at 400rpm less to maintain the same speed does what?

You get some difference from pumping loss/friction loss, etc. but I'm not sure the difference is as significant as you think. I'd suggest tire choice matters more, and 2WD vs 4WD certainly matters more. If I was actually concerned with eeking out the best fuel economy I'd look for the lightest tires with the lowest rolling resistance I could find, 2WD, aerodams and drive like I'm going to my own funeral.

KoboldTaco · Jul 15, 2022

ramffml said:
My bad, I'm not actually offended nor did I read your post that way. I tend to come across that way on the internet (I've stumbled across my own posts from months ago and thought "wow, that sounded harsh" ).

Anyway, I wasn't defensive, just showing that there are more than two sides to the argument. Your "argument" (and what I've seen posted here many times) is that trucks aren't supposed to care about mpg because it's not a prius. My response to that is, some of us "need" the truck for doing truck-y things sometimes, but still want to eek out the best mpg we can when it's just used to go from point A to point B. It's not silly or wrong to want this. It's wrong to expect 30 mpg, yes, but not wrong to aim for maximizing mpg as best we can (hence my gear choice).

I have a relatively light "level 2" big horn. 4x4 CC. My payload is 1750 so that gives a bit of reference as to how light it is, most 5th gens are several hundred pounds less in payload.

I turn off MDS because I feel that it doesn't work. One of those ideas that work in theory but not in practice so much. My best results so far have all been with MDS disabled. My last record of 9.4 was also with MDS disabled.

MDS basically turns off half your engine and stresses the other half (basically 4 cylinders running WOT) but lugging while doing it (low rpms but high load = bad). It shakes sometimes in and out of MDS. I have no facts or data to support this, but I'm convinced it's better for the life of the engine to let it coast around easily with 8 cyliders firing, vs running 4 at pretty high load.

No worries brother and thanks for explaining. I should also be less sensitive and projecting emotion on the interweb is just hard.

We all want to keep as much money in our pocket for sure in today’s day and time. I suppose I just gave up in a sense - I like it when I get 20+ with my 6.7. yet to happen but I get close every now and again on the highway. Also with regard to giving up; living in California - well the gas prices are just plain ugly. If I think about it too much, I get mad so I suppose that is where I give up lol.

I’m looking forward to the post mileage report with my Banks Monster Ram installed. I have seen guys get more after installing it but that was not the primary reason. I was looking for the airflow gain and removing the crap design on the heater grid.

MDS - reminded me of when I used a similar feature when I rented a Chevy Taho once. It would nerf the engine to a 4 cycl on the highway and other less stressful situations for the rig. I was really impressed how much it did extend the base mileage.

ramffml · Jul 15, 2022

Docwagon1776 said:
So MDS causes the motor more 'stress' to run the same speed but running at 400rpm less to maintain the same speed does what?

There is an RPM for every load and MPH, where revving higher is wasted fuel, and revving lower is "lugging" and causing stress. I can't tell you what that point is.

I can tell you, that my 3.21 in 8th gear does not feel under powered. It climbs many little hills on the freeway without requiring a downshift. I can speed up without requiring a downshift. It's not lugging, or even close to it.

If I let it drop into MDS, it's always on the edge, cycling back and forth between MDS on/off. Just breathing on the pedal or looking at it sideways causes the silly thing to deactivate. In other words, it can't do it. Those 4 cylinders cannot run my truck for anything other than absolutely steady on a level or decline with a stiff tailwind and even then it just randomly drops out of MDS.

That's the difference. My truck isnt lugging with the 3.21 because it has more than enough power to drive it.

Docwagon1776 said:
You get some difference from pumping loss/friction loss, etc. but I'm not sure the difference is as significant as you think. I'd suggest tire choice matters more, and 2WD vs 4WD certainly matters more. If I was actually concerned with eeking out the best fuel economy I'd look for the lightest tires with the lowest rolling resistance I could find, 2WD, aerodams and drive like I'm going to my own funeral.

I'm not sure what you're trying to say here. What difference isn't signifcant? Agreed with you on tire size, rolling resistance, aerodams, and driving style.

rmill · Jul 15, 2022

ramffml--you are an excellent spokesman for the 3.21, especially when it comes to towing! Have read several of your posts and you are spot on. I am convinced everyone who bashes the 3.21s towing capabilities, have never towed with it. "your truck isn't going to like it" is my favorite. I go as fast as i want towing a 6500lb trailer with no problems. 10 to 12 mpg all day long. Sorry it's a little off topic.

FYI, i would kill for your payload.

Docwagon1776 · Jul 15, 2022

ramffml said:
I'm not sure what you're trying to say here. What difference isn't signifcant? Agreed with you on tire size, rolling resistance, aerodams, and driving style.

400rpm and the friction/pumping losses of that vs the energy required to keep the vehicle moving at the speed vs wind resistance, rolling resistance, etc.

ramffml · Jul 15, 2022

Docwagon1776 said:
400rpm and the friction/pumping losses of that vs the energy required to keep the vehicle moving at the speed vs wind resistance, rolling resistance, etc.

That should be easy enough to test, next time I can force the transmission into 7th for a while and see what the ECU reads. In any case, I've never seen a high mpg with a 3.92 so statistically speaking if you want to maximize mpg you're best shot is definitely with the 3.21. No doubt tires and wind play a major role as well which is why the rebel gets the worst mpg all around; worst tires, worse aero, worst gear ratio.

Docwagon1776 · Jul 15, 2022

ramffml said:
That should be easy enough to test, next time I can force the transmission into 7th for a while and see what the ECU reads. In any case, I've never seen a high mpg with a 3.92 so statistically speaking if you want to maximize mpg you're best shot is definitely with the 3.21. No doubt tires and wind play a major role as well which is why the rebel gets the worst mpg all around; worst tires, worse aero, worst gear ratio.

I guess I could test it by driving 65.

Nahhh.

dhay13 · Jul 15, 2022

I had a 2007 1500 4.7 3.92's and best I ever got was 16.505. Average over 55,000ish miles I put on it was 14.207

Next was my 2013 1500 5.7 3.55's. Best I ever got in it was 19.850 and average over the 65,000ish miles I put on it was 15.524

Now with my 2018 2500 6.4 4.10's my best so far is 16.813 with an average over 20,000ish miles is 12.028

All are hand calculated

My EVICs are typically about .5 to .8 lower than hand calculated but I have had a few where the dash readout was actually lower than my hand calculated

Socalramfan · Jul 15, 2022

IDSandman said:
You were on a freeway going 43mph? Lol!

At least get out of the left lane when he does :waytogo:

Socalramfan · Jul 15, 2022

I’m kind of laughing at some of the comments, and that we, as Ram truck owners are fussing over MPG.

I can only speak for myself, but I bought and mod’ed mine to have fun and enjoy without a single thought towards MPG.

Miles per Smiles are more important to me

Colt4thHorseman · Jul 16, 2022

I also get this kind of gas mileage (25-27) out of my hemi about 65 mph on long stretches of straight flat interstate driving.

Zoe Saldana · Jul 16, 2022

crazykid1994 said:
Idk if yours is that way but when I used to get 18-19mpg my computer said 19-20mpg. Now that I get 12-13mpg my computer will say anywhere from 13-15mpg. It’s almost always been 1-1.5mpg off when I had calculate.

If I understand you question - I believe hand calc vs computer.

And the higher the mpg on the computer the more off it is vs hand calc.

Sweetee · Jul 16, 2022

My bad, but I do like to follow and sometimes chime in on threads dealing with MPG. I see that there are 2WD, 4WD, Cummins, 5.7, CC, QC and probably RC folks contributing to the discussion. Now I'm throwing in a 3.6 driver just to totally add to the mix.

It seems to me that unless there is a truly scientific comparison of like equipped trucks with the the same components except 3.21 vs. 3.92 the discussions are flawed to begin with. I don't doubt most claims of mpg but would trust hand calculations over the EVIC. When you hand calculate you are dealing with verifiable data (miles divided by gallons/litres). However, there can even be problems with that depending on the sensitivity of pump shut-off, topping off consistancy and even slope of the fuel stations pavement.

I have a '17 Laramie, 3.6 4x4, 3.55 axle with topper, boards bed mat and me(220 and and fully fueled the truck weighs 6010lbs) and I can eek out an EVIC reading of 29+ on my 20 mile trip home from our local Costco. I always clear the EVIC with every fuel-up and hand calculate every tankful. I have a permanent record in my logbook but also use FUELLY.COM for both our vehicles. In everyday around town it is consistently between 22 and 24mpg. Since July 2017 my average calculated mpg is 20.7. I also have several long distance trips pulling my 14x7 cargo trailer(4000 to 5000 lbs.) which has skewed the overall average. My best longer distance non-towing trip was 27.6 in the middle of winter.

With all that said, I know full well I am not a "lead-foot." I run the speed limit on two lane roads and usually set the cruise at 60 on the freeway(Is there a left lane?). Here in southern WI we're seeing our prices coming back to the $4.00 mark finally. However, my driving style has not changed since the higher prices and because of the covid shut-down my monthly average for miles driven has dropped from 650 miles a month to about 400 miles a month. I know I'm rambling, but with my wife laid up with a non-covid virus and shingles, I guess I needed to be able to talk to anyone!

With all that said, good luck to those who like their trucks no matter what the MPG and $ is and good luck to those who, like me, like to "pinch a penny" and eek out the best mpg possible. We are a homogenous group who should be able to coexist with all our difference preferences. Finally, having just had service done and having a chance to kick tires while waiting, I went online and built a new '22 Laramie just like mine. I'll have to pinch a few more pennies I guess. With the topper and tube steps, and bed mat, a new '22 prices out at over $12,000 more than mine was 5 years ago. Hand calculated that is a 23% increase. YIKES! Take care, be safe and enjoy your truck!

Socalramfan · Jul 16, 2022

Sweetee said:
My bad, but I do like to follow and sometimes chime in on threads dealing with MPG. I see that there are 2WD, 4WD, Cummins, 5.7, CC, QC and probably RC folks contributing to the discussion. Now I'm throwing in a 3.6 driver just to totally add to the mix.

It seems to me that unless there is a truly scientific comparison of like equipped trucks with the the same components except 3.21 vs. 3.92 the discussions are flawed to begin with. I don't doubt most claims of mpg but would trust hand calculations over the EVIC. When you hand calculate you are dealing with verifiable data (miles divided by gallons/litres). However, there can even be problems with that depending on the sensitivity of pump shut-off, topping off consistancy and even slope of the fuel stations pavement.

I have a '17 Laramie, 3.6 4x4, 3.55 axle with topper, boards bed mat and me(220 and and fully fueled the truck weighs 6010lbs) and I can eek out an EVIC reading of 29+ on my 20 mile trip home from our local Costco. I always clear the EVIC with every fuel-up and hand calculate every tankful. I have a permanent record in my logbook but also use FUELLY.COM for both our vehicles. In everyday around town it is consistently between 22 and 24mpg. Since July 2017 my average calculated mpg is 20.7. I also have several long distance trips pulling my 14x7 cargo trailer(4000 to 5000 lbs.) which has skewed the overall average. My best longer distance non-towing trip was 27.6 in the middle of winter.

With all that said, I know full well I am not a "lead-foot." I run the speed limit on two lane roads and usually set the cruise at 60 on the freeway(Is there a left lane?). Here in southern WI we're seeing our prices coming back to the $4.00 mark finally. However, my driving style has not changed since the higher prices and because of the covid shut-down my monthly average for miles driven has dropped from 650 miles a month to about 400 miles a month. I know I'm rambling, but with my wife laid up with a non-covid virus and shingles, I guess I needed to be able to talk to anyone!

With all that said, good luck to those who like their trucks no matter what the MPG and $ is and good luck to those who, like me, like to "pinch a penny" and eek out the best mpg possible. We are a homogenous group who should be able to coexist with all our difference preferences. Finally, having just had service done and having a chance to kick tires while waiting, I went online and built a new '22 Laramie just like mine. I'll have to pinch a few more pennies I guess. With the topper and tube steps, and bed mat, a new '22 prices out at over $12,000 more than mine was 5 years ago. Hand calculated that is a 23% increase. YIKES! Take care, be safe and enjoy your truck!

Best wishes for the Mrs’s as well :waytogo:

hemihustlin · Jul 17, 2022

Wild one said:
There's a theory floating around,that the trucks actual exhaust system,might be a bigger contributor to manifold bolt breakage,then we think.Example being the 5.7 cars use basically the same cast iron log manifold,but with a set of dual pipes,that lead back to an X farther towards the rear of the car,then the trucks squashed midpipe is,and the cars don't break manifold bolts. The theory does make you wonder if the actual exhaust system on the trucks might be putting more stress on the back manifold bolts,then we think,as it's always the back bolts that break,which is where the exhaust pipes would be exerting the most pressure.You'd think if it was totally heat related and temp changes breaking bolts,the front bolts and middle bolts would be more inclined to break,but i've never seen or heard of a truck actually breaking a front manifold bolt

excellent! add this to the list of reasons why to get a custom xpipe set up haha :superhack:

Zorin · Jul 17, 2022

Hahahaha, this thread reminds me of the 2018 Ram 1500 I rented for my old job. Fun story here...

At my old job, we used to play "Distance To Empty Showdown" with vehicles we rented. Well, one day, I got the call to get some parts to client right now. 1000 pounds worth of bearings. No sweat.

Went to Enterprise, rented a Ram 1500 Crew Cab with a Hemi, back to the office, loaded it, and took off.

Drove from Wichita, KS, up to Wood River, NE, and BACK to Salina, KS on one tank of fuel.

Mind you, I was NOT driving calm, or gentle, or hypermiling, and I was hauling a load. (Probably holding somewhere between 70 and 75, with the A/C cranked on Max) But I also still had to deliver for DTE Showdown.

Start Mileage - 12,113
Mileage at re-fuel - 12,603
Total distance - 490 miles.
Fuel pumped - 25.962 Gallons
Fuel Mileage - 18.87 MPG.
EVIC stated 20.2 MPG.

I also still have the standing record for DTE Showdown, as I pumped 25.962 gallons into a truck that had a 26 gallon fuel tank. I drove the thing probably 50 miles on the low fuel warning!

I only have all of these figures because I posted it all on Facebook, hahahaha!

Tim

Docwagon1776 · Jul 18, 2022

ramffml said:
That should be easy enough to test, next time I can force the transmission into 7th for a while and see what the ECU reads. In any case, I've never seen a high mpg with a 3.92 so statistically speaking if you want to maximize mpg you're best shot is definitely with the 3.21. No doubt tires and wind play a major role as well which is why the rebel gets the worst mpg all around; worst tires, worse aero, worst gear ratio.

Think the easier load on the motor may let it stay in MDS mode for longer as well? Which is more fuel efficient 400rpm higher on 4 cylinders or 400 less rpm on 8? If we're concerned about eeking out maximum mileage, shutting off MDS seems to be counter productive as it's proven to inject less fuel per cycle.

bchap05 · Jul 18, 2022

I remember the old days when I bought my 3.21 and I'd get back from highway trips at 24 mpg. But that was stock tires and height, no weight from my camper shell. After the lift, tires, and readjusting my speedo I was more like 19 and after adding my shell more like 18.

ramffml · Jul 18, 2022

Docwagon1776 said:
Think the easier load on the motor may let it stay in MDS mode for longer as well? Which is more fuel efficient 400rpm higher on 4 cylinders or 400 less rpm on 8? If we're concerned about eeking out maximum mileage, shutting off MDS seems to be counter productive as it's proven to inject less fuel per cycle.

I think the results speak for themselves; if I can get 27 mpg with MDS disabled then it's not doing much of anything. My gut says there should be a tiny gain running with MDS, but it's hard enough accepting this kind of MPG, I don't think there is much room left on the table to improve it. The gains of MDS appear to be more theoretical, pretty much all the gas that went to the 4 cylinders that are now turned off, is now sent to the 4 cylinders that are running twice as hard. The efficiencys come due to reduced pumping losses; an engine that is running at or near WOT is more efficient than an engine running at 1200 RPMs.

The reason I don't use MDS is not due to fuel economy. I turn it off because I don't believe stressing those 4 cylinders is good for the engine and I don't like the feeling it has going in/out of MDS.

To answer your question, what's better, to run 3.21 without mds or 3.92 at 400+ rpms higher with MDS, I really don't know for certain. But I do know that all the high MPG numbers I've seen have been with the 3.21.

And lets face it, if there was even the slightest possiblity that the 3.92 was more efficient, Ram would not offer the 3.21 at all. Why would they? These guys are now prescribing ditch water instead of 30 weight oil, carefully selected minivan tires, active grills, and increased oil temps, all to save a fraction of an MPG.

This MPG is why I bought the 3.21

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