NV3500 ratios are
4.01-2.32-1.40-1.00-.73 O/D with splits of .58-.60-.71-.73
Notice the truck "granny"gear.
To make best use of od, you might want a rear gear of 3.55s This will get you 65mph @2266,with 25inch tires. But low gear will be 3.55 x 4.01 = 14.23. This much gear is good for hauling grain off a soft field, and not much else. So with first gear useless, tou are left with a 3 +1 box;with a brutal starter gear of 2.32 x 3.55 = 8.24. So 3.55s are out and so is anything bigger.
Lets work it from the bottom.
A good teener Duster starter gear would be 11.0/1 So;11.0/4.01 = 2.74s. So we/ve got first working. Howsabout O/D? 2.74 x .73 =2.00FD. This will get you 65 @1749. This would be fine for a stock-cammed teener.
So 2.74s are gonna work. Anything bigger you rapidly lose first gear, and it would be very difficult to use 2nd as a starter gear.
Now, letr's say you get tired of lookin at those teeny 25s back there, and graduate to 28s which fill up the tubs pretty nicely. A recalculation shows that now you will need 2.94s to best use od and low.
Ok so lets just put the 28s on right away, and the 2.94s too. Good to go right?
Not so fast,grasshopper. Lets talk about the splits.
Ima gonna assume you are wanting to set this up as a streeter. And that teener might have some bite to it; so let's say you are running the ever-popular 268 cam. This cam likes some revs to get moving, so lets say,around town you are gonna shift it at 3300. So lets go; into first with 2.94s and 28s, 3300 will be 23mph, and yank it into 2nd.At the shift the Rs will drop to 58% so that makes 1914 Rpm. Teener got torque?
Lets continue; 3300 in 2nd will be 40mph;and the Rpm drop of 60% puts the 3rd gear Rs at 1980. Teener got torque?Let's continue; so now you are in 3rd and accelerating to cruise speed; 3300 will be 66.8MPH .But you have two gears to go! So you dump into OD and the Rs come down to 1721,perfect. But you skipped 4th. So what have you got? Running as a streeter you have a 3 plus 1, with very wide splits. This tranny demands an engine with a very low operating powerband. Just like the stock Magnum or V6 that it came out of.
So what to do? Get rid of the cam. Move up to a 3.23. Sacrifice a little o/d for a little better 2-3-4 and rev it a little higher in 1st and 2nd, that's what.
-So how will that look? Again with 28s and 3.23s(or 3.55s with 25.5s,works out the same), Lets run her up to 3500 in first.OK.That makes 22.5mph and at the shift into 2nd the Rs drop to 2030. Teener got torque? It does now, with the stock cam.So now, lets buzz it up to 3500 in 2nd to make 38.9mph. The rpm drop into 3rd will be 2100, but lets calm down a bit now and buzz it up to just 3000 in 3rd. So that will get us 55mph, and the rpm drop into 4th gets us 2130. Finally you motor it up to 65@2520, and drop it into o/d;1840rpm.Pretty sweet?
Maybe.
But look at all the sacrifices you made; 1)Small, hi-torque engine required. 2) exactly two pumpkins will work and only with matching tires, 3) Lotsa reving going on for brisk acceleration.,4) limited torque rating,5) tunnel mods, 6) truck shifter,etc
Now my opinions
-It is my opinion that if you just want a nice cruiser car, and your teener has a stock cam and is otherwise healthy, and that you are willing to drive it this way forever,and that you are willing to swap the rear out to what you need, then go for it.
-I posted this elsewhere;for a nice tranny performance-ratio spread, you take the lowest gear and divide it by the highest gear ratio, and the result should fall between 4.0 and 4.5 tops. The NV3500 is 4.01/.73 = 5.5. This might be a nice spread in a farm truck, but it is way too huge for Duster with anything but a stock teener.
-Ima telling you this so that you will know what to expect in the end.After the many hours spent to fit it in there, and all the additional monies spent to finalize the install.
-All the best to you in your endeavors.
