hi i have been looking at a 1985 w350 it has a 360 4BBL/727 D60 in the front and D70 in the rear the owner said he thinks the ratios are ether 3:73 or 4:10 but was not sure. i am using the diffs only and would like to know avalible ratios for that year. thanks  mark  

Should be a 4.10 but if you are planning big rubber, do not concern yourself with what ratios are in them because even a 4.10 is not enough and you will need to change them anyway  if you want it to run right and have drive train last too. A 4.10 is a good gear for a full sized 4x4 with stock sized tires but not with big tires.  

Question-Is 4.10's too high for 36" tires with a BigBlock? -402/TH400/208- I seem to go from a stop pretty easy and I can still go 90mph on the highway. It doesn't bog down at all either. 4Lo is great too. I would like to go with 4.56 or 4.88 but I feel it is too low and gas mileage would eat my wallet alot worse. What about the trucks with a Duramax, running 37's and putting 4.10's in them? Why does that work so well? I know there is alot of guys where I live that change their ratios and love it. I'm just curious on all this.  

Even for a big block, 4.10s is a bit tall for 36's. Also if you are really worried about MPG, you would not run a BB and 36's. AS far as a Dmax comparison, those engine redline at about 3200 RPM and are not happy at that RPM either. Their torque is higher but it peaks at a lower RPM so you tend to need taller gear. On this torque thing just remember that 600ft lbs at 1500 RPM makes the same HP as 300ft lbs at 3000 RPM. Gas engine have different power curve and therefore need different gears to do their best.