Gearing for gas milage 1

[bmxdirt234]

If i went from a 3.70 gear ratio and went to a higher gear for gas milage, what kind of power would i need to make to make up for the gearing loss?

Truck:

Stock 2004 2500 quad cab dodge 4x4 w/35in tires. It has 3.70 rear end in it.

Any suggestion on where i can find info or what i need to figure it up myself would be appriciated.

Thanks

Paul

 

[kellnerp]

...At 60mph i am running about 1750rpm. The real problem i am having is when i get on the highway and drive 70 or 75mph,...

Do you think the fact that wind resistance increases 56% from 60 to 75 mph has anything to do with this?

To compensate you have to reduce your drag coefficient by 56%. From the looks of it the best you can hope for is a 30% reduction (see Drag coefficient study #1, Drag coefficient study #2, Drag coefficient study #3).

A big air dam in front and a half height cap seem to be the way to go.

TOP
CSWP, BSSE

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[dgallup]

Short stroking a car crusher might reduce the frontal area 56%.

 

[waross]

Maybe I'm way off base here, but I would look for a chart of engine efficiencies versus RPM and gear so that I could keep my RPM in the best part of the curve.
Is this information not available?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[GregLocock]

For most vehicles that information is a little hard to come by. You need the mass and rolling resistance, and the drag coefficient and frontal area, and the BSFC map for the engine, and the gear ratios.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[kellnerp]

You can put the vehicle on a chassis dyno and obtain that info. If you want to be a purist, put it on a chassis dyno and then remove the engine and put it on a dyno and map the engine both ways. Then compare and the two.

TOP
CSWP, BSSE

http://www.engtran.com

http://www.niswug.org

"Node news is good news."