Gear Ratio (rant)

[truckguy82]

The 5.3 can put out probably as much as 150-160 hp in v4.

I seriously doubt that, the engine is rated for 355hp, so if you tuned it to stay in v4 mode all the time and put it at wot, it might be making 150hp tops.

[Nanotech Environmental]

I seriously doubt that, the engine is rated for 355hp, so if you tuned it to stay in v4 mode all the time and put it at wot, it might be making 150hp tops.

So, in other words - what I said.

[truckguy82]

So, in other words - what I said.

Well considering it's impossible to go WOT in v4 unless you specifically tuned for it, which nobody would ever do, it's not what you said.

 

V4 might be capable of 50-60hp tops

[Nanotech Environmental]

Well considering it's impossible to go WOT in v4 unless you specifically tuned for it, which nobody would ever do, it's not what you said.

 

V4 might be capable of 50-60hp tops

Not to be pedantic, but the intent of my post was to show the possible potential of peak power in V4

See key words 'probably as much as' (the implication intended to be; what it could do if it could reach peak power rpm in v4)

 

My apologies for not wording it more clear.

[aseibel]

Yes, the main variable being the amount of hp produced is dependent upon air temperature. At 65, my truck rarely spends time in V4, where at 75 it does, as stated. Pulls right up small inclines at 75 that at 65 would have it going to V8. As I said, after 11k miles of data collection, 70-75 mph is the sweet spot at 60*. 50-55 mph is the sweet spot at 35*. 65* is the sweet spot at 80*. The "sweet spot" being optimum fuel mileage. Data runs being the average between head-tail winds, north-south, east-west, etc.

 

I know you have watched your fuel mileage a lot and think it is heavily dependent on temperature. Well I live in Wisconsin and have driven in over 100 degrees F of temp fluctuations from below 0 to the upper 90's. I can tell you your fuel mileage depends way more on SPEED than air temp.

 

I can specifically remember my best ever trip mpg. I was driving exactly 60 mph in September- around 60-70 degrees outside.

 

no vehicle that drives on the ground is most efficient at 75 mph. It is a fact that vehicles are more fuel efficient at or below 50 mph because any speed greater than that creates excessive wind drag. I challenge you to put the cruise control on 60 mph for 1 hour and tell me what mpgs you get.

 

http://www.caranddriver.com/columns/driving-for-fuel-economy

 

"Aerodynamic drag increases with the square of vehicle speed, and the engine power required to overcome aerodynamic drag increases with the cube of vehicle speed, so going 18 percent faster—from 55 mph to 65—increases drag by nearly 40 percent and requires 65 percent more engine power."

[Cowpie]

That is all true. Something many of us in heavy commercial trucking figured out many, many years ago. And it even gets deeper than that. The rolling resistance of the tires even plays into it. And "sweet spot" in an engine is a factor of where the engine is running at a RPM where the fuel consumption curve is the lowest. Just like RPM and Torque, any engine has a fuel consumption rate under load that is variable based on RPM which is affected by rotational inertia and other factors. And low RPM does not always equate to lowest fuel consumption rate per hour. The fuel consumption rate is a an U shaped curve on the graph. Unfortunately, the OEM's and others don't ever seem to provide that kind of info. Heavy vehicle engine OEM's and industrial engines, one can get that kind of info from them. With smaller vehicles, one has to just play with various RPM's to figure out this kind of thing.

[Nanotech Environmental]

That is all true. Something many of us in heavy commercial trucking figured out many, many years ago. And it even gets deeper than that. The rolling resistance of the tires even plays into it. And "sweet spot" in an engine is a factor of where the engine is running at a RPM where the fuel consumption curve is the lowest. Just like RPM and Torque, any engine has a fuel consumption rate under load that is variable based on RPM which is affected by rotational inertia and other factors. And low RPM does not always equate to lowest fuel consumption rate per hour. The fuel consumption rate is a an U shaped curve on the graph. Unfortunately, the OEM's and others don't ever seem to provide that kind of info. Heavy vehicle engine OEM's and industrial engines, one can get that kind of info from them. With smaller vehicles, one has to just play with various RPM's to figure out this kind of thing.

Yet, you gear your trucks(big and small) to get ~10-20% worse mileage than they'd otherwise get if they had sensible gears in them..........

[barry G]

to the op..

your rant is legit.

My dad was complaining about his 2016 in just a few weeks.

the manual mode is great, the 6 speed.. but it chooses what ricer scream to stay in with automatic downshifts.

 

 

..and my 1996, it peaks at 22mpg in the summer 14in the winter

-20 to 100

air temp has alot to do with gas mileage. Don't forget, the all aluminum even has to monitor humidity.

The iron just needs to warm up.

 

my old 305 outpulls the brand new truck...with a 5 speed.

I keep it in overdrive torturing a uhaul dolly and a subaru wagon thrashed like a toy back there...about 4k pounds.

Fuel mileage does not even change loaded or empty..

 

the manual wins.

the 3.73 is a proven gear. I trade it for nothing.

[Cowpie]

Not quite sure what you are getting at, 3beejay3. What "sensible" gears would that be for, say, my larger trucks? Part of sensible rear ratio gearing is also factoring in the transmission gear ratios also. With the pickups, there are not options on transmissions. On larger trucks, a plethora of transmissions with varying gear ratios are optional. And the typical speeds one is running at and the roads and terrain factor in also.

 

Now, let's take my current Freigthliner semi. It has a 12.7L Detroit 60 engine, behind that is a Eaton 18 speed with two overdrives. Behind that is two differentials with 2.64 gear ratios. The truck never operates higher than 16th gear, which is direct drive, which is the most efficient transmission ratio with the least parasitic loss. The engine, at 65 mph, is at 1500 RPM, which is the prime spot for the engine to run in (1400-1500 RPM). This semi has averaged, over 690,000 miles, 7.93 mpg. That is roughly 23% higher mpg than the class 8 truck/dry van national average. If I used the two overdrives in the trans, the identical engine speed would be at 65 mph and 1500 RPM with 3.55 diff ratios and running in top trans gear. But, it would be slightly less fuel efficient, as the overdrives have a higher parasitic loss than direct drive.

 

Given that the area and roads i typically use my 6.0L 2500 on, 4.10 diffs and 5th gear max does a pretty good job on fuel economy. Local running, I am typically in the 14-15 mpg range. On major highway trips at 65 in 6th gear, 17-18 mpg averages are common. I have not seen anyone with 3.73 do much better than those numbers with a 2500 6.0L. I have narrowed that the 6.0 L96 I have seems to deliver the best fuel economy in the 1800-2200 RPM range. There is less shifting on hills and such when keeping the RPM's in that range. And, I am not revving the engine up too high to counter the efficiency.

 

Now, I am probably going to really tank the mpg in July. Will be taking the pickup on a 2000 mile round trip and am primarily going to use E85. The prices are fairly good along that trip route for E85 right now. Will see how it compares, on a cost per mile basis, to regular E10. Sure, the mpg will take a hit, but the lower cost, it may actually be cost effective. Price spread is averaging 50 cents a gallon lower for E85 on that route I will be taking. It may not be worth it, but I want to see the actual numbers. I know what I have gotten for mpg on E85 in the past, but never on a full road trip. At 4 mpg less with E85, that would be a wash on cost per mile compared to E10 regular. The times I have used E85, the mpg has been about 3 mpg less on E85 as opposed to E10. At that level, E85 is actually cheaper per mile to use.

[tnchevy]

to the op..

your rant is legit.

My dad was complaining about his 2016 in just a few weeks.

the manual mode is great, the 6 speed.. but it chooses what ricer scream to stay in with automatic downshifts.

 

 

..and my 1996, it peaks at 22mpg in the summer 14in the winter

-20 to 100

air temp has alot to do with gas mileage. Don't forget, the all aluminum even has to monitor humidity.

The iron just needs to warm up.

 

my old 305 outpulls the brand new truck...with a 5 speed.

I keep it in overdrive torturing a uhaul dolly and a subaru wagon thrashed like a toy back there...about 4k pounds.

Fuel mileage does not even change loaded or empty..

 

the manual wins.

the 3.73 is a proven gear. I trade it for nothing.

You must have one rare and very special 20 year old truck! I have owned several manual 305 and 350 GM trucks and they can't come close to pulling what these newer trucks can. I also never seen 22 mpg on a 305 or 350 (mine had 3.73 or 4.10's). The best I ever saw was around 17 mpg on the highway. The 305 had some low end grunt but it runs out of steam pretty fast, especially compared to these newer drive trains.

[Nanotech Environmental]

Not quite sure what you are getting at, 3beejay3. What "sensible" gears would that be for, say, my larger trucks? Part of sensible rear ratio gearing is also factoring in the transmission gear ratios also. With the pickups, there are not options on transmissions. On larger trucks, a plethora of transmissions with varying gear ratios are optional. And the typical speeds one is running at and the roads and terrain factor in also.

 

Now, let's take my current Freigthliner semi. It has a 12.7L Detroit 60 engine, behind that is a Eaton 18 speed with two overdrives. Behind that is two differentials with 2.64 gear ratios. The truck never operates higher than 16th gear, which is direct drive, which is the most efficient transmission ratio with the least parasitic loss. The engine, at 65 mph, is at 1500 RPM, which is the prime spot for the engine to run in (1400-1500 RPM). This semi has averaged, over 690,000 miles, 7.93 mpg. That is roughly 23% higher mpg than the class 8 truck/dry van national average. If I used the two overdrives in the trans, the identical engine speed would be at 65 mph and 1500 RPM with 3.55 diff ratios and running in top trans gear. But, it would be slightly less fuel efficient, as the overdrives have a higher parasitic loss than direct drive.

 

Given that the area and roads i typically use my 6.0L 2500 on, 4.10 diffs and 5th gear max does a pretty good job on fuel economy. Local running, I am typically in the 14-15 mpg range. On major highway trips at 65 in 6th gear, 17-18 mpg averages are common. I have not seen anyone with 3.73 do much better than those numbers with a 2500 6.0L. I have narrowed that the 6.0 L96 I have seems to deliver the best fuel economy in the 1800-2200 RPM range. There is less shifting on hills and such when keeping the RPM's in that range. And, I am not revving the engine up too high to counter the efficiency.

 

Now, I am probably going to really tank the mpg in July. Will be taking the pickup on a 2000 mile round trip and am primarily going to use E85. The prices are fairly good along that trip route for E85 right now. Will see how it compares, on a cost per mile basis, to regular E10. Sure, the mpg will take a hit, but the lower cost, it may actually be cost effective. Price spread is averaging 50 cents a gallon lower for E85 on that route I will be taking. It may not be worth it, but I want to see the actual numbers. I know what I have gotten for mpg on E85 in the past, but never on a full road trip. At 4 mpg less with E85, that would be a wash on cost per mile compared to E10 regular. The times I have used E85, the mpg has been about 3 mpg less on E85 as opposed to E10. At that level, E85 is actually cheaper per mile to use.

To put it simply, you're gearing and/or driving your vehicles such that they run several hundred RPM higher than they need to. If you're running the Detroit at 1500 at 65 mph, you're too high and are wasting fuel and forcing extra wear on the motor, engine oil etc., etc. Yes, you are! I hope you aren't leaving it in 16th when unladen...

Comparing to the National average is a very poor comparison, as the newer trucks all get much worse mileage since the new smog regs came out 2-3? years ago. To do it right, you need to compare directly to similar years and similarly equipped trucks making similar runs with similar loads.

 

Honestly, you're only fooling yourself if you think that that 6.0liter gets the best mileage at 1800-2200rpm on the hwy. 17-18mpg is pretty low for that truck on the hwy at moderate speeds & light loads. Drop the RPM at 65 to 1500 and you'll get 19-20 mpg, plus get more time between oil changes, and much less engine wear.

It's just the facts.

All the stuff about peak operating RPM etc. is just a method guys use to fool themselves. I've seen guys use that logic on other forums and it just does - not - work,... even on paper.

Ultimately it's your choice if that's what you want to do, as it's perfectly well within your rights, but just be clear and up front about that. Don't claim that it is the best, most efficient way, when it isn't.

 

Simply put, the best approach to overall fuel efficiency is reducing engine rpms as much as possible for any given load at a given speed.

 

Jus sayin'

[dorkweed]

I tow my work trailer around suburbia 5+ days a week. My work trailer only runs about 3500lbs; but my truck has no problems towing it every day of the week, even with 3:42rears and the 6 speed.

 

On weekends I pull my boat......................7000+lbs..............No problem on hills, boat ramps, wind, etc.

 

Troll regards.

[Cowpie]

Actually, 3beejay3, I was being more than fair in my comparison. I was comparing my fuel economy numbers with current model trucks averages. My truck, while it is a 2013 Freightliner, it has a MY 2000 Detroit 60 DDEC IV pre-egr engine. Now if we go back to the year 2000, the average fuel economy nationwide for similar trucks doing similar work was around 5 mpg instead of the current 6.5 mpg. So instead of getting 23% better fuel economy, compared to the same model year engine, I am getting over 50% better fuel economy. The truck itself is identical Columbia model that was built in 2000, so no advantage there either. And doing what I doing will shorten engine and oil life? Every HD diesel I have owned I took to over 1 million miles without a major repair. This one has 697,000 miles and uses no more oil than day one. And I take the oil changes to 50% longer than the OEM recommended drain interval. Oil samples are taken at each oil change.

 

But you think I should run the RPM's lower on that Detroit 60 DDEC IV engine. Well, what is the RPM where peak torque is reached? What RPM does it start to drop off? At what RPM point does the Borg Warner 171702 turbo get to 90% efficiency and higher? And if I am running 900F EGT's on a hard pull at 1500 RPM, what would be the EGT's at 1300 RPM and why does it matter?

 

Sure that is a Detroit Diesel, but some things carry over even to a naturally aspirated engine. One aspect to getting maximum efficiency, exhaust flow must be kept above a level where restriction is not a drag. Exhaust cools immediately after leaving the head. If the flow is not fast enough, the exhaust cooling too quickly down stream because it is moving too slow will create a bottleneck for exhaust that is leaving the head. That can be shown in increased EGT's and that bottleneck can have a negative effect on fuel efficiency. And while your argument has some merit if all I was ever doing was driving on flat ground, unloaded, with no wind, or in town, I hardly ever see those wonderful scenarios. If I run lower RPM's than I am, then on the hilly, curvy two lane roads I frequent, the trans would be shifting frequently. That has a considerable negative effect on fuel economy. By keeping down a gear and keeping RPM's a tad higher, actually it is more efficient. Also in doing that, I am better overcoming engine rotational inertia when I need power on a pull on a hill. On those rural hilly, curvy road, I typically will run in 5th gear, at 58 mph and turning 2100 RPM. On highway, I will let it go to 6th, and at 65 be turning about 1900 RPM.

 

And I have never seen on any forum where someone with a 2500 and 6.0L, even with 3.73 as opposed to 4.10, consistently averaged 19-20 mpg. Actually, I have been berated frequently that I am lying in saying I have pulled off 17-18 mpg with mine on road trips. So I think you are stretching the argument a little too far and straining at a gnat to make your point. There is no appreciable data that shows anyone is consistently getting 19-20 mpg on highway with a 6.0L 2500, even when they are diligently trying and even with 3.73 as opposed to 4.10.

[Nanotech Environmental]

Actually, 3beejay3, I was being more than fair in my comparison. I was comparing my fuel economy numbers with current model trucks averages. My truck, while it is a 2013 Freightliner, it has a MY 2000 Detroit 60 DDEC IV pre-egr engine. Now if we go back to the year 2000, the average fuel economy nationwide for similar trucks doing similar work was around 5 mpg instead of the current 6.5 mpg. So instead of getting 23% better fuel economy, compared to the same model year engine, I am getting over 50% better fuel economy. The truck itself is identical Columbia model that was built in 2000, so no advantage there either. And doing what I doing will shorten engine and oil life? Every HD diesel I have owned I took to over 1 million miles without a major repair. This one has 697,000 miles and uses no more oil than day one. And I take the oil changes to 50% longer than the OEM recommended drain interval. Oil samples are taken at each oil change.

 

But you think I should run the RPM's lower on that Detroit 60 DDEC IV engine. Well, what is the RPM where peak torque is reached? What RPM does it start to drop off? At what RPM point does the Borg Warner 171702 turbo get to 90% efficiency and higher? And if I am running 900F EGT's on a hard pull at 1500 RPM, what would be the EGT's at 1300 RPM and why does it matter?

 

Sure that is a Detroit Diesel, but some things carry over even to a naturally aspirated engine. One aspect to getting maximum efficiency, exhaust flow must be kept above a level where restriction is not a drag. Exhaust cools immediately after leaving the head. If the flow is not fast enough, the exhaust cooling too quickly down stream because it is moving too slow will create a bottleneck for exhaust that is leaving the head. That can be shown in increased EGT's and that bottleneck can have a negative effect on fuel efficiency. And while your argument has some merit if all I was ever doing was driving on flat ground, unloaded, with no wind, or in town, I hardly ever see those wonderful scenarios. If I run lower RPM's than I am, then on the hilly, curvy two lane roads I frequent, the trans would be shifting frequently. That has a considerable negative effect on fuel economy. By keeping down a gear and keeping RPM's a tad higher, actually it is more efficient. Also in doing that, I am better overcoming engine rotational inertia when I need power on a pull on a hill. On those rural hilly, curvy road, I typically will run in 5th gear, at 58 mph and turning 2100 RPM. On highway, I will let it go to 6th, and at 65 be turning about 1900 RPM.

 

And I have never seen on any forum where someone with a 2500 and 6.0L, even with 3.73 as opposed to 4.10, consistently averaged 19-20 mpg. Actually, I have been berated frequently that I am lying in saying I have pulled off 17-18 mpg with mine on road trips. So I think you are stretching the argument a little too far and straining at a gnat to make your point. There is no appreciable data that shows anyone is consistently getting 19-20 mpg on highway with a 6.0L 2500, even when they are diligently trying and even with 3.73 as opposed to 4.10.

Hey, As long as you're happy. Think what you want. Believe what you want. Just be honest that it's what you want to do, and that you're using 1/2 math as well as cherry picking facts and datum to support your beliefs.

Here's what I do know for sure: Let's take 2 identical GM fullsize pickups. You put the rear end gears you want in yours and drive it the way you think you should. I'll put the gears I want in mine. Then, we both drive an identical 500 mile course(with some variety of terrain, etc), at the same time in the same conditions. I'm fully confident that my overall average fuel mileage is significantly better than yours at the end of the trip.

[runsdeep]

You would think I said something bad about your family.

 

 

A half ton is fully capable of pulling a side by side or two.

 

I am not happy with the rear end gears and how I ran at 3 grand for 70% of a 5 hour ride.

 

If you like your truck, thats great, but I never said anything about your truck.

 

My whole point was just to say its ridiculous to not offer some more choice in gears from the factory.

 

And how would a 3/4 ton with less hp and just a heaver frame and suspension haul better than a 1/2 ton with comparable gears when all you haul is about half the limit of a 1/2 ton.

You are right about the choice of ratios avail. from GM in the 1/2 ton. But I can tell you this coming from a 14 1500 5.3 3:42 to a 2500 4:10 gasser is night & day difference!! go drive one!. You forgot to mention better, bigger brakes, axles, drive shaft heavy duty cooling etc. over any 1/2 ton GM builds. I pull a heavy arse 9200 lb TT back & forth from FL to MI.did that one time with my 1/2 ton never again it was not a good pull up/down the Smokey mtns. I say buy the right tool for the job & quit complaining about just the rear gear ratio...02 worth.