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Old 04-29-2018, 07:10 PM   #10
Palf70Step
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Join Date: Jul 2002
Location: Gulfport, MS USA
Posts: 47,491
Re: Optimum RPM for 305 MPGs

Quote:
Originally Posted by RedBed View Post
Here's the funny thing - now that I swapped in a 4L60, my MPGs went from about 12.5 (old 3-spd) down to 9.5 (4L60). Then last week I had a trailer with a heavy load, and stayed out of OD. My average jumped UP to over 10.5.

So I installed a tach. My current RPM are 1900 @ 65. And that is the spot where my MPGs s-u-c-k.

So this tank I am going to drive around without using OD at all. We'll see what happens to the MPGs. My guess is that they will jump up, and if so then I will need to swap out differential gears.

Using a calculator online It seems like my diff gears are possibly 3.73... I don't know what they are. But I have 29.1" tires, and using 3.73 as the gears, it comes in about right.

So if it happens like I think it will, I'll need to figure out what gears to swap to.
Did you recalibrate your speedometer gears to match the new transmission. You may be getting better than you thing for MPG.
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