C20 milage improvements

[mrein3]

Originally Posted by ezglide

stuff deleted...

Now that said heres the conflict, I do have that little adapter sticking out of the transfer case too, kinda makes me wonder if the 1st owner did some mods to the truck? I bought it from my step dad and am the 3rd owner.

I would do the math if I had the formula! LOL! <- Means laughing out loud.

I'm guessing that with 20% taller tires, and the factory 3.07 speedo corrector unit (I don't know what they're called) between the speedo cable and the x-fer, you're probably reading the correct mileage. Meaning you're probably right on with your mpg calculations.

A good way to check to see if your speedo is on and therefore you mileage calculations are correct is to drive down the road with a GPS. In relative terms a GPS is way more accurate than just about anything out there. Set the GPS to read speed. On my old 5-channel Eagle unit it is "SOG" or Speed Over Ground. Place the unit where the antenna isn't shielded by the truck and where you can see the display without causing you to not pay attention to the road and drive around a bit. If your speed reads the same as your GPS, you know your calculations are correct.

If your speedo isn't correct, you may be getting better mileage than you calculated. Or worse. Without a correct speedo your odometer is off and you don't have good data.

On the RHS of your rear axle facing forward is a three letter code stamped in the axle tube. Write that down then get on the google and search for Chevy rear axle codes. That will tell you what your rear end ratio is.

If your data is good, and you think you may want to go with a 700r4, click over to the 4x4 and off road forum and ask if anybody over there runs 33" tires, 3.73 rear end gears, and a 700r4 before you start spending money. These forums are full of helpful people. In all likelihood somebody there has a K20 with a small block, 3.73 gears, and 33" tall tires. The chances are they'll be more than helpful.

Some links on the 4x4 forum:
http://67-72chevytrucks.com/vboard/s...ighlight=700r4

http://67-72chevytrucks.com/vboard/s...ighlight=700r4

One more thing. When I was researching putting a 700r4 in my 4x4, I found that the Advanced Adapters output shaft is cheaper from Summit than from Advanced Adapters. Go to the AA website, get the AA part number for the correct shaft, then search on Summit's website for that part number.