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I assume this is an LQ4 and NV4500? Near or The last year for that transmission.I wouldn't go less than 3.73:1 on a 2500 series GMT800. It'll be a dog. On par with the 350, SM465, and 2.73:1 (2.79??) gears in my old 85 C10 that's been repurposed into Chinese soup cans. You might get away with it if you had the 8.1L but not the LQ4.You will not be able to re-calibrate to 3.21:1 gears using a Tech 2. Not sure what HP Tuners will do for your PCM but it will not talk to the ABS computer and both need to be changed.I'm running a 2005 Silverado 2500HD with the LQ4, 4L80E, NP263, 4.10:1 gears in an AAM 10.5" 14bolt, and 265/70R17 tires on N89 wheels. I get 13mpg in mixed country 2 lane driving. 3.73 would probably bump me up to 14. That's great mileage for the LQ4.I'd put 3.73 gears and 265, 275, or 285 tires on it. You can calibrate the ABS computer with a Tech 2 for the 265 & 275 tires... Maybe the 285 tires... not positive. I used HP Tuners for the PCM.Most tire outfits won't mount the 265 and wider tires on the 16x6.5 PY0 Al wheels or Steels. That's why I moved up to the N89 17x7.5 wheels.
There's a point of diminishing returns on fuel mileage. 3.73:1 is that point on the 3/4 ton's. You may get away with 3.54:1... but you can get to the same place with larger OD tires and 3.73:1 gears... tires are easier to change back. It's similar to the 305 getting better fuel mileage than the 4.3L V6 in a truck that had essentially the same options other than the engine. Lower displacement should yield better fuel mileage forever with the right gearing... Right? Nope... it's actually a bell curve.While the 364CI Gen III LQ4 has similar final torque and higher HP numbers than the MK V 454 it doesn't have the low RPM torque curve to match. There's no replacement for displacement and the old MK V has 90CI on the LQ4. The MK V 454 is already up around 300ft lb at or before 3,750RPMs. The LQ4 doesn't get there til you tach it up another 1,000RPMs to 4,750.And... You don't ever want to tow with the NV4500 in 5th gear. 5th gear walks off the end of the mainshaft if you're too rough on it.
The Cummins Inline 6 Diesel that Chrysler put in the Ram Trucks is a torque monster. It makes a LOT more torque than any stock gasoline engine way down low in the RPM bands and Peak torque on the relatively tame 1988 5.9L with the early Bosch VE pump was 400Ft-Lbs. The 1988 engine pushed out 300Ft-Lb at under 2500RPMs and by the mid 90's it was over 300ft-lbs at 1500RPM or less...If you want a diesel in a GMT800 just sell the LQ4 truck and buy one with an LB7 Dirtymax. 500Ft-Lb at 1600RPM in 2001.Diesels are kinda like a slutty, hot, high-maintenance woman. I've had both. Fun to look at and fun to ride but you don't want to have to pay for them.I'm old enough to be quite sick of the less than reliable nature of all of the offerings the big 3 put out in the last 30 years or so. The LQ4 is almost as bulletproof as the old 350 smallblock with better fuel mileage and lower maintenance.
Quote from: hatzie on November 18, 2018, 01:31:06 PMThe Cummins Inline 6 Diesel that Chrysler put in the Ram Trucks is a torque monster. It makes a LOT more torque than any stock gasoline engine way down low in the RPM bands and Peak torque on the relatively tame 1988 5.9L with the early Bosch VE pump was 400Ft-Lbs. The 1988 engine pushed out 300Ft-Lb at under 2500RPMs and by the mid 90's it was over 300ft-lbs at 1500RPM or less...If you want a diesel in a GMT800 just sell the LQ4 truck and buy one with an LB7 Dirtymax. 500Ft-Lb at 1600RPM in 2001.Diesels are kinda like a slutty, hot, high-maintenance woman. I've had both. Fun to look at and fun to ride but you don't want to have to pay for them.I'm old enough to be quite sick of the less than reliable nature of all of the offerings the big 3 put out in the last 30 years or so. The LQ4 is almost as bulletproof as the old 350 smallblock with better fuel mileage and lower maintenance.I would never have a diesel. I look at the overall cost to operate one in $ per mile with the added fuel prices and high cost of maintenance is the main reasons why. Give me a SBC or a BBC carb'd and I would be happy. The 2001 will be sold whenever I get one of my square body trucks moved up to DD status. I know exactly what to expect out of those old school set ups. Just trying to improve on what apparently is about the best I could expect out of it.