Gear ratio and diff swap question---more or less efficient?

[Bob98SR5]

Ok, I'm gearing illiterate. What can i say :smokin:

Alrighty my current Mercedes' gear ratio is 2.65. However, my donor Mercedes' gear ratio is 3.27. As I understand gear ratios, that means that currently, the engine spins the driveshaft 2.65 times to turn the wheels one revolution. So when I do the switch, my car must turn the driveshaft 3.27 times : 1 tire revolution.

I am sticking with the same stock tire size. So I'm thinking that the car will feel more lively when i press the gas, but it will be more of a fuel hog b/c it must work harder to turn the wheels, right?

anyone with knowledge, please enlighten me :)

[4runnerchevy]

You are correct, see your not gear illiterate :thumbup:

[Bob98SR5]

fargin' A, this is not what I want at all. but then again, these mercedes are a little slow off the line.

[elripster]

You gotta love Mercedes. They make a car and just lower the gearing with the engine displacement. Clearly the donor vehicle had the smaller engine. It will move out better but probably not be more efficient with that lower geared diff. That's a 23% difference, that's rather large.

Frank

[Bob98SR5]

yeah it looks like my only option is to remove the old diff and put it in the new axle. its a huge difference like you said, frank. hopefully its bolt on or else im in for more headaches!

[elripster]

When I used to be on the diesel benz bbs a lot (www.mercedesshop.com) every once and a while someone would swap the other way and wonder why they couldn't get up hills to save their lives. At least you won't have that problem. You'll be hill climb king.

Frank

[BruceTS]

you have to remember that a diesel runs at a lower RPM compared to a gasoline engines, that's why they have taller gearing....

[Bob98SR5]

When I used to be on the diesel benz bbs a lot (www.mercedesshop.com) every once and a while someone would swap the other way and wonder why they couldn't get up hills to save their lives. At least you won't have that problem. You'll be hill climb king.

Frank


frank,

thats where i hang out mostly for mercedes info :) but im definitely not going to swap that 3.27 in there. im keeping it as stock as possible

[elripster]

you have to remember that a diesel runs at a lower RPM compared to a gasoline engines, that's why they have taller gearing....


Agreed. I was more referring to, for example, what we in the US know as the 300D and 240D were also sold in Europe as a 190D or maybe 200D, I can't remember but as the engine size drops the diff ratio does too. The smallest engine has a top speed of like 80MPH.

Frank

[arjan]

Isn't it generally true that a smaller numerical gear ratio will give you a better fuel mileage (within reason)?
Of course bogging down an engine won't do your mileage any good either.