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Gears and regears

Kyle Petterson

NAXJA Forum User
Location
Raleigh, NC
Quick question. 89 4.0 aw4 242 3" lift w/ 31's. I have factory 3.55's in it right now - I should have 4.10's. My question is this: What will 4.10's do to my a) gas mileage (I know, it's a brick, and the gas mileage doesn't bother me as it is now. To be honest, I'm not even sure what it's getting, but if it's going to be worse w/ 4.10's then we may have a problem. I do 90% on road/highway) b) top speed c) climbing hills at high speed.

I know that gearing will make a big difference off road, but anybody who has done the swap w/ a similar setup, I'd like to know what you have to say about the above topics.

Thanks. Here's a picture of an owl. :eek:wl:
 
4.10's and 31's will have you running higher RPM's on the highway and probably not as good as milage, but maybe better then your getting right now. You will notice a power gain w/ the deeper gears. IIRC, 3.73's would get you back close to stock gear ratio w/ 31's. I know that I was getting @ 16 MPG w/ 4.10's and 32's on my old daily driver. w/ the 4.10's your power will be there for you climbing hills at speed and you will acheive your top speed faster, but also higher RPM's to boot.

Thanks for the picture of the owl.....
 
climbing hills at high speed is where you will see the biggest advantage with 4.10. when going up hills, that is where you get the most resistance/load and regearing will allow you to power up those hills without coming out of OD.

adding larger tires requires more power to turn them. since your engine cant provide more power, you need to change the gears in the gear train. basically a lower gear change provides a longer lever to turn the tires. its simple mechanical advanatge.

actually when offroad, you can use 4lo to make up for the change in tire size. which is essentially lowering the gear ratio of the drive train
 
Going to 4.10's will improve your mileage. Right now, your engine is working "extra" hard to keep you moving forward, like you were towing a couple of jetski's behind you all the time.

The 4.0 doesnt mind spinning a little fast - 2800-3000 RPM's for hours on end don't bother it at all.

Asking it to work hard all the time, it will take, but suck a lot of gas.

.. and it will drive a lot nicer with deeper gears.
 
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