I guess it is a matter of how you read it. If 'a diesel' means 'every diesel' you are right, of course. But I think that the big picture is that in some cases it may be a good idea to explore changing the gear ratio to improve mileage. In my view, the percentage will depend on the particulars. You may lose or gain.

JL

Exactly right.

There is no disagreement that a reduction in engine speed will improve the fuel economy of a vehicle with a diesel engine. You definitely will not lose.

The issue is whether or not your percentage gain exactly matches your axle ratio change. This was his original premise.

i will concede everything if someone has hard evidence to refute my experiences.

i will also concede that my statement near the end of my post in which i stated the savings would equal the ratio change is not very likely to be true except in some exceptional situation. but my statement in the first part of my original post said nearly equal, and i will stand by that.

now we can argue about what nearly means, i suppose, but i would like to see evidence.

even engineers eventually have to put the car on the road and see if their calculations are correct.

even mercedes conducts extensive road testing and we all agree they have the best engineers in the world, right?

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

You've got some evidence that suggests that you get better fuel economy with taller rear axle ratios. Nobody will refute this.

Nobody will refute this either.

Nobody knows what "nearly equal" means so nobody is going to refute this either.


Thanks for your post.

and you dont have any hard evidence, do you?



tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Let me pose a question to you.

This is especially appropriate since you're an architect.

A fellow comes in to you and tells you that he used a 2" x 4" header above his garage door.........a garage with a second story above. He tells you that the header was fine and it supports the load perfectly.

Now, as an architect, you clearly know that this fellow is full of $hit and there is no way that such a header can do the job.

But, he claims to have the evidence that supports his position.

Do you accept his evidence.......or do you realize that he is clearly in error and that 2" x 4" is already bending significantly and may fail in the not too distant future?

Of course, you don't have any hard evidence to refute this fellow......because you'd never do anything so stupid as to put a 2" x 4" above an 8' door.

The analogy is identical.

and you dont have any hard evidence do you?

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I'm sorry to tell you that you.......as the thread starter........have the onerous of providing the hard evidence. You've provided anecdotal stories without a shred of hard evidence concerning a back to back test on a M/B diesel.


And, you've clearly ignored the very good analogy of an architect who would laugh in the face of someone who demanded hard evidence of the fact that a 2" x 4" won't work as a proper header above an 8' garage door.

You do know that this header would be inappropriate.......don't you?? Maybe I'm making some cavalier assumptions regarding your knowledge of building construction??

it just seems that to refute anecdotal storys with other anecdotal stories just doesnt cut the mustard...engineering wise i mean.

and i am not sure you understand what a 2x4 is... or a header. you know, not being an Architect and all.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

...........sorry you didn't understand the analogy.........oh well.........as I mentioned several times in this thread........you can believe what you want.

My goal is to simply present the facts for other members....................

They can make their own judgment of whom to believe.............three engineers............or an architect without good data.

but you really don't have the hard data for a na diesel, do you?

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

i happened to think to look at their web site.

for a dodge they offer three applications:
1. 28.6% od on an older four speed = 25 to 28% better fuel economy.
2. for the five speed trucks they offer a 22% od and say it = 20% better economy.
3. and for a six speed like mine they offer 28% od and claim 20% better fuel economy.

they don't say whether it is for diesel or gas, but they have power graphs for all the recent gas and diesel engines. the 5.9 cummins for example has a torque peak at 1300 rpm and max hp at 2750.

when i am towing with mine i shift at 3000 and it drops the rpm down to about 2000 and thus keeps the boost on pretty well.

i dont know if they have used actual engineers on these figures or not.

you can decide for yourself whether this qualifies as near the same percentage or not.

they also offer them for cars with a lot of pro street and such shown. i didn't look at that though.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Hi Tom,
It would appear from the information posted on their site that Brian may owe you if not an apology, at least a concession that you are right in many instances.
I looked at all the figures for GM, Dodge and Ford trucks, and in most cases, they indicate a mileage percentage increase at or almost at the ratio percentage change. In a few cases where the final drive ratio is already at the low end they also indicate much less of an increase.
It just goes to show that many vehicles are not optimized for best mileage, even in these days of high priced fuel.
I do suspect that vehicles with less surplus horsepower and torque will show less of a gain, and that it would be quite possible to overdo the principle to the point that there would even be a mileage drop.

Regards,

__________________
Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C

I'm reaching back to remember a magazine story on your "double nickel" in the early days... a Volvo wagon consumed more fuel in overdrive than it did in the straight ratio at 55 mph.

My anecdotal architectural contribution here is intended to cast a critical light on the legacies of that profession...

In old England, the Monarchy had identified two lengths of wood for the stoves, and of course the gentry had the longer. The peasants stacked their wood up against the inside walls of their "houses". Thus the basis for the 16 inch pitch in 2 x 4 construction, and 24 inch for 2 x 6.

Now, perhaps the modern architect has a mathematical engineering model which shows the maximum safe pitch of the studs in the wall, eight foot garage door or not.