A Pickup Truck Project

[Big Dave]

I don't view my truck as a lead zeppelin at all. I get nearly double the MPG that most guys get with diesel pickups this size and nearly triple what one-ton gas pigs get.

Yeah, I haven't gotten to 30 MPG yet. I gotta work on my aero package but I think the gearing is there. Phil Knox' strictly aero work success should get me motivated.

My truck does not have a 9 inch. It has a Sterling 10.25 inch rear axle.

[max_frontal_area]

Originally Posted by Big Dave

I don't view my truck as a lead zeppelin at all. I get nearly double the MPG that most guys get with diesel pickups this size and nearly triple what one-ton gas pigs get.

Yeah, I haven't gotten to 30 MPG yet. I gotta work on my aero package but I think the gearing is there. Phil Knox' strictly aero work success should get me motivated.

My truck does not have a 9 inch. It has a Sterling 10.25 inch rear axle.

Big Dave, the refference was towards your attempt to motivate OEMs to follow your suit. i know a bit about attempting to motivate americans and changing their ways, USUALLY they are motivated by $$$, and in turn it will take a motivated american to change the way the big 3 conduct business.

approaching 30 mpg seems unreal in a big vehicle like yours. i have done wonderous things in pint sized euro shuttles, but this f-250 XT is my first pickup and lemme tell you it is a brick, and it dont even run ;~>

with your overdrive what is your final drive ratio? your sterling axle is it OEM?

[Big Dave]

My Sterling 10.25" is factory. Nine inchers got into half-ton trucks.

Overall top gear ratio stacks up like this: (3.08)(0.72)(0.78)

OEM-size rubber 31.7 inches O.D.

70 MPH @ 1310 RPM

You are dead right about one thing. This truck long enough ceased to be an economic exercise. Now it has taken on a new purpose: Show everyone - both consumers and OEMs - that big and MPG are not mutually exclusive.

I'd like to see these truck get a 7 or 8 speed dual clutch transmission (no torque converter) and a 3,31:1 axle ratio. The 8 speeds allows a numerically high initial gear to get a load moving but still spinning slower at road speeds.

The 3,.73 and 4.10 gears usually seen on diesel trucks are mostly there to give the lame automatics a chance to hold together past warranty.

[TEiN]

Originally Posted by Big Dave

Now it has taken on a new purpose: Show everyone - both consumers and OEMs - that big and MPG are not mutually exclusive.

I'd like to see these truck get a 7 or 8 speed dual clutch transmission (no torque converter) and a 3,31:1 axle ratio. The 8 speeds allows a numerically high initial gear to get a load moving but still spinning slower at road speeds.

[raises hand]


I'll take one.

[DieselFan]

Hi Big Dave

Your experience with the Gearvendor overdrive unit has me considering one for my Ram 3500 4x4, 6sp, 3.73 rear end. However, highway rpm would fall to around 1500 from 1925 with the current stock setup.
Isn't that a bit off peak fuel efficiency for the 5.9 L Cummins, I read that they are most efficient at 1950 rpm but then I don't want to end up driving at 80 mph as wind resistance would kill the potential fuel efficiency gains.

I am a bit surprised at the 15% gain you seem to attribute to the gearvendor that lowers the rpm by 22%. At highway speed, around 40 wheel hp is necessary to move a 7500 lb truck and the rest (a major portion) is to compensate for wind resistance. The overdrive unit will reduce losses due to engine and auxiliairies operation but will do nothing to offset losses due to wind resistance and the 7500 lb of weight. I would have expected no more than 10% gains from a 22% reduction in rpm. What's wrong in my thinking?
Ivan

[oil pan 4]

Originally Posted by DieselFan

highway rpm would fall to around 1500 from 1925 with the current stock setup.
Isn't that a bit off peak fuel efficiency for the 5.9 L Cummins, I read that they are most efficient at 1950 rpm.

I have herd that too: "the [any engine] is most efficient between [always some number between 1800 and 2200]RPMs"
I don't know maybe it gives the peak for fuel economy and power, that could be what they mean for "most efficient".
I also noticed EVERY one that says that is getting well under 20mpg.
Trust me they say the same thing over on dieselplace.com on the 6.2L and 6.5T forums.
The guys with the 4x4 6.5T turning 1800 on the highway, with a non-over drive transmission on 4.10 gears are only getting about 15mpg.

I have adoped nearly the same setup as big dave.
Diesel engine, with a trans that has a lock up converter and a .72 over drive (makes it act a lot like a standard trans), with 3.08 rear gears and 31'' tall tires.
My truck chugs along at 1250RPMs @ 55mph and 1350RPMs @65mph and it got 26 to 27mph with out drafting or hypermiling.
I can get over 30 when drafting. The first time I drafted for more than 10 or 20 miles I went for nearly 400 miles and pulled off the high way to fill up convinced my fuel gauge was broken, nope I was just getting a little over 31mpg drafting off a big uhaul going about 55mph.

What people are saying is best and what we test are 2 differet things.
I say go with the tried and tested set ups and stay away from the old wives tails.

[rmay635703]

Originally Posted by DieselFan

Hi Big Dave

Your experience with the Gearvendor overdrive unit has me considering one for my Ram 3500 4x4, 6sp, 3.73 rear end. However, highway rpm would fall to around 1500 from 1925 with the current stock setup.
Isn't that a bit off peak fuel efficiency for the 5.9 L Cummins, I read that they are most efficient at 1950 rpm but then I don't want to end up driving at 80 mph as wind resistance would kill the potential fuel efficiency gains.

Just because your engine can make power the most efficiently at X does not mean you will get the best FE steady state generating 400hp.

You need to look where your motor most efficiently generates the amount of HP you need to move and that may well be near wot at low RPMs.

Unless of coarse you P&G.

Originally Posted by DieselFan

What's wrong in my thinking?
Ivan

Driver variability, an overgeared vehicle allows a talented individual to get far more FE or someone with no clue to get less.

[DieselFan]

Thanks Oil Pan 4. So you think my 6 sp with 3,73 rear end would be a good match to simply add a Gear Vendor and operate at 1500 rpm at 60 mph is that what I should understand?

Originally Posted by oil pan 4

I have herd that too: "the [any engine] is most efficient between [always some number between 1800 and 2200]RPMs"
I don't know maybe it gives the peak for fuel economy and power, that could be what they mean for "most efficient".
I also noticed EVERY one that says that is getting well under 20mpg.
Trust me they say the same thing over on dieselplace.com on the 6.2L and 6.5T forums.
The guys with the 4x4 6.5T turning 1800 on the highway, with a non-over drive transmission on 4.10 gears are only getting about 15mpg.

I have adoped nearly the same setup as big dave.
Diesel engine, with a trans that has a lock up converter and a .72 over drive (makes it act a lot like a standard trans), with 3.08 rear gears and 31'' tall tires.
My truck chugs along at 1250RPMs @ 55mph and 1350RPMs @65mph and it got 26 to 27mph with out drafting or hypermiling.
I can get over 30 when drafting. The first time I drafted for more than 10 or 20 miles I went for nearly 400 miles and pulled off the high way to fill up convinced my fuel gauge was broken, nope I was just getting a little over 31mpg drafting off a big uhaul going about 55mph.

What people are saying is best and what we test are 2 differet things.
I say go with the tried and tested set ups and stay away from the old wives tails.

[DieselFan]

I looked up a Cummins report showing lb of fuel per hour at various rpm and it had the lowest consumption at 1950 rpm. I don't know how much load was put on that engine during the test though.

[oil pan 4]

They could be testing for the highest BSHC (Brake Spesific Horse Power Consumption).
That is when you calculate how many how many pounds of fuel per hour it take to maintain each and every horse power for an hour.
They were likely testing under heavy load.

You are going with a set up that sounds like what I want to do with my car.
Big displacement engine, that makes big torque on 6-speed and looking for great MPGs.
In my car I would like to install a T56 with the new engine and swap out the rear later after road testing the 3.08s (It also has a 3.08 rear end). I would like to see what happens in top gear at 65mph turning 1150rpms.
I would like to try for over 30mpg on a 500hp V8.

I am guessing you have a 6 speed with a .7ish top gear, 4.10 rear end and 31'' tires.
The cheapest way to change your final drive ratio is to swap rear end gears.
If you replaced 4.10 gears with 2.73 (or what ever is close to that in the dana's) you would drop your RPMs from about 2000rpm to 1350rpm.
Or if you went with 3.08s you would drop your engine RPMs to 1500 at 65mph.

Yes you can tow with that.
I was able to pull 3 tons with my old worn out 6.2L on my current trans/diff/tire setup.
I am not going to be doing any heavy towing like that any more, so after my turbo goes on I am considering going from 3.08 to 2.73.

Also remember the bigger the rearend gear teeth the stronger the ring and pinion are. A 3.08 is stronger than a 4.10 because the 3.08 has big knoby teeth compared to the 4.10.

Correction above my truck engine turns about 1300@55mph and 1550@65mph.