[racehauler]

Got a question about my trucks gearing. It's a 2wd cc dually with 4.10's and it will only get about 16 to 17 mpg highway, city whatever and 11 ish pulling my race car trailer.

I have been tossing around the idea of regearing to a 3.73 or 3.55
Tire size on the truck is the stock 215-85-16 so they are pretty short.

What could I expect for milage gains? What about towing...gain or loss in MPG?

How much pulling power will it loose while running along at 60 to 65 MPH towing a trailer?
I really hate it when you have to shift down for every little hill when towing, do you think that would be the case if I changed the gearing?

 

[House]

keep the 4.10s, had 3.73 swapped in my fsuperduty from the 4.63 and the 3.73s sucked now went to 4.10s and love it

 

[gregrob]

Downshifting depends on the power.

I like the 4:10's in my buddie's 97 for towing ONLY, everything else it sucks and it's way too low.

Not sure what MPG you'd pick up. I'd say at least 1-2mpg at the same speed. It's nice to be able to run 70 at 2000rpms....

 

[racehauler]

Downshifting depends on the power.

I like the 4:10's in my buddie's 97 for towing ONLY, everything else it sucks and it's way too low.

Not sure what MPG you'd pick up. I'd say at least 1-2mpg at the same speed. It's nice to be able to run 70 at 2000rpms....

I kind of like them while towing up until I get on the interstate and run 75 to 80 MPH. That's approaching 3000 RPM on this beast and I'm sure milage will suffer. Guess I could just not go as fast :hehe: like that will ever happen.

I have just been kicking the idea around of 3.73's but I will get a better idea of what I think of interstate towing in a month when I head to Boone, Iowa.
90% of the driving I do I don't run over 70 MPH, so maybe it aint even worth it.

 

[Pocket]

90% of the driving I do I don't run over 70 MPH, so maybe it aint even worth it.

With a statement like that, it ain't worth it to gear swap.

However, it is sad to see that you drive like a granny all the time :hehe:

 

[Dave Whitmer]

No doubt about it. Dropping the ratio will improve your MPG. Doing so (at the same road speed) cuts your engine RPM, thus your engine frictional HP.

I went from 3.73s to 3.08s and picked up 3 MPG in my mixed city/suburban (35%), Interstate (30%) state roads (35%) driving loop. Actually its my 42 mile one-way commute. Why did i go to 3.08s? because i couldn't find any 2.73s.

I don't tow much but when I do, its dense but not draggy loads (10,000 lb of shingles, 8,000 lb of machinery, and the occasional Bobcat). Pulling 10,000 lb of shingles through eastern KY (short steep hills) at night where I couldn't coast at all I got 15.5 MPG. My all time best was 29 MPG lightly loaded all Interstate.

One caution: If you have an automatic, I would not recommend going to less than 3.55. If you slow the engine down you also cut ATF flow through the cooler and a cooked tranny can result. I had a GMC with the wimpy 6.2 and a TH400 but added a Gear Vendor overdrive. That rascal went through transmissions like a teenager through potato chips. Five dead TH400s. spectacular failures - parts and oil scattered down the road. i never thought i'd see the day when something would kill a TH400 but the low end gruunt of even a wimpy dioesel will do just that.

With a manual, no problem.

I intend to much lower but I need someone who can custom-hob hypoid gears for my sterling 10.25.

 

[Pocket]

I had a GMC with the wimpy 6.2 and a TH400 but added a Gear Vendor overdrive.

Dave, my parents had the same setup in a Chevy Suburban. Even without the Gear Vendor it was guaranteed that transmission would fall apart constantly. They replaced or rebuilt it every single year they owned it. Pretty sad really, that thing was a pig. But at least I know they weren't the only ones with the same problem.

 

[Dave Whitmer]

Pocket posted:
“But at least I know they weren't the only ones with the same problem.”

Dave says:
And the problem is/was by no means limited to GM. Ford automatics fail way too often. Dodge automatics fail way too often. Even the Allison 1000 behind high-revving Duramaxes fail way too often.

Manuals go through clutches at a variable rate depending on the driver. The NV4500 had the tail bearing nut problem but otherwise sticks are very reliable. That’s why even with arthritic football knees I want nothing to do with an expensive, frail, and inefficient automatic.

Racehauler posted:
“90% of the driving I do I don't run over 70 MPH, so maybe it aint even worth it.”

Dave says:
‘Tain’t so! By slowing down the engine at any road speed, you cut the engine frictional HP and thus reduce fuel burn

Hopefully, sometime this fall I intend to do some zero torque fuel burn tests in order to quantify fuel savings from reduced engine RPM. I have an AIC so I can set the engine to “idle” at any RPM I like. If I can put a couple of valves into my fuel system I can use a graduated container to measure fuel burn over a 10-15 minute period at a given zero torque RPM. To get a better feel I’d disconnect all the electrical loads possible so only the engine is in play. Get a figure for fuel burn at an “idle” at 1000, 1100, 1200 (a target RPM for me), 1300, etc up to about 2500 RPM. Then I can tell you how much fuel you are burning just to turn the thing over at a given RPM.

I need to find some new helpers. My old helpers got whacked with the useless stick and I don’t have Sapp’s talented hands myself.

 

[gregrob]

lol
Love reading your posts Dave

 

[southmike]

maybe a gear venders overdrive..
you can keep your 4.10's and get lower gears when you need them.

 

[southmike]

I was looking at the gear venders overdrive..
you can keep your 4.10's and get lower gears when you need them.
not sure if your suppose to tow with it or not.

 

[Dave Whitmer]

If I remember right, a GV overdrive is a 0.8:1 ratio. When engaged, it makes you 4.10 into 3.28. I don't think any automatic will withstand that very long.

Thing is the Powerstroke engine is a torque monster and if you do not have a gawdawful load and in hilly terrain, the engine laughs at a paltry 3.28. It sneers at my 3.08. You will get greedy, liking the economy and quiet operation and run with the overdrive engaged too much and then you will find yourself raking up transmission parts along the road.

Now if somebody like Brian or Suncoast tells you their transmission will take heavy overdrive use (pushing two stages of overdrive), I'll defer, but unless a top transmission shop tells you otherwise, my money is on the OD trashing your automatic.

 

[Madvan]

Dave

I read somewhere IH testing showed that the 7.3 PSD was most fuel efficent at 1450 rpm. Dont remember if that was with splits or singles. Testing was on 300HP marine version motor. I will see if i can dig it up.

Bill

 

[Dave Whitmer]

You have to be a little careful when talking a common parameter called brake specific fuel consumption (bsfc) and absolute fuel burn.

BSFC is important if you operate a lot of the time heavily loaded like boats or Class 8 trucks. Most pickups operate at a somewhat lower road load, so best fuel economy can be had below the BSFC peak at a lower RPM.

I operate at 1450 @ 60 MPH and it does run sweet there (EGT=400 degrees).

 

[racehauler]

I kind of forgot about this thread. Sorry guys. :lame:

There are several good points mentioned for and against it. If I were to change gearing I don't think I would want to go any further than a 3.73. I have this truck to pull my race car trailer, hence my user name, and that's pretty much it's only function...well other than the occasional :tree:

Pocket wrote:

However, it is sad to see that you drive like a granny all the time

NO! I just don't like getting tickets. I live in Kansas man, it's 50 miles to the closest interstate so I'm driving 65 mph speed limit roads 90% of the time.

David Whitmer wrote:

Racehauler posted:
“90% of the driving I do I don't run over 70 MPH, so maybe it aint even worth it.”

Dave says:
‘Tain’t so! By slowing down the engine at any road speed, you cut the engine frictional HP and thus reduce fuel burn

Dave you must keep in mind I am pulling an enclosed car trailer (flat front) that weighs aprox. 12K lbs. when I am wanting to gain fuel economy.

I recently took a 450 mile round trip towing the trailer the entire time. I was running 75 to 80 mph 70% of the trip and 65 to 70 mph 30% of the trip. My average economy was 10 mpg. I have been averaging 10.7 mpg on 60 to 70 mph driving pulling the same trailer.

David Whitmer wrote:

I went from 3.73s to 3.08s and picked up 3 MPG in my mixed city/suburban (35%), Interstate (30%) state roads (35%) driving loop. Actually its my 42 mile one-way commute. Why did i go to 3.08s? because i couldn't find any 2.73s.

If I changed from 4.10 to 3.73 that would be a 9.02% change in gear ratio. You changed from 3.73 to 3.08 that would be a 17.43% change in gear ratio. If the percent of gear ratio change would affect fuel milage proportionally on my truck towing a trailer as it did your truck driving empty (probably wont happen, but for the sake of disscuson we will assume) then I would expect to see a 7.06% gain in fuel economy (this assuming that your economy gain of 3 MPG was going from 19 MPG to 22 MPG and getting a final gain of 13.64%). A 7.06% gain in fuel economy would equate to a .75 MPG gain on my truck

The math:

19 MPG = .1364 = 13.64%
22 MPG


9.02% gear ratio change = ______X_____
17.43% gear ratio change 13.64% MPG gain

X = 7.06% MPG gain on my truck

7.06% (or .0706) * 10.7 MPG = .755 MPG gain

Everyone follow?

I think I am talking (well typing) myself out of the gear change idea...

 

[Dave Whitmer]

Racehauler:

A couple of thoughts.

Reducing your 70 MPH engine RPM from 2200 RPM to 2000 will help you some but the huge road load imposed by your heavy, draggy trailer will make it look trivial and probably wreck your automatic.

But there is another, cheaper alternative open to you.

When does your race season end?
I've been looking for somebody who drives a draggy trailer around a lot. Most RV guys only make a handful of moves a year, but a racer might be out all spring, summer, and fall.

You seem to keep decent records and should be able to drive repeatably.
I have some ideas that might help you out. It might cost a couple hundred bucks tops and be well within your skill set. You game? If so, PM me.

 

[quick26]

race hauler, i had a 97 with the 3:55 gears and 33" tires. it had a rough time pulling my enclosed trailer at anything above 70. i only had a down pipe, k&n and a programer though. the tranny would get a bit warm also.

 

[racehauler]

Yeah, I think I'm going to hold off on the gear change for now anyway. It looks like Dave has some other ideas. I'll have to see how that works out.

 

[bigcountry250]

I know when I went to 4.56's my hwy mileage went all to hell, but I love the performance! If you go 3.73 you will def get a lil better mileage on the hwy but the low end pulling won't be as strong.

 

[00PSD1]

I kind of like them while towing up until I get on the interstate and run 75 to 80 MPH. That's approaching 3000 RPM on this beast and I'm sure milage will suffer. Guess I could just not go as fast :hehe: like that will ever happen.

I run at 3000 rpms day in and day out and I have no problems :ford:

-
Andrew