Speedometer calibration on a 2001 Silverado 2500HD?

[zieg85]

I am considering a differential gear change to my 2001 Chevy.  I am thinking about swapping in a 3.21 in place
of the 4.10.  Since the truck was offered with the 4.10 and 3.73 only my question is can it be calibrated for
3.21 gearing?  The transmission is a standard shift 5 speed and from what I've read has the same gear ratio
spread of a SM465 in the first 4 gears and the 6.0L should have enough grunt over a bone stock 454 in my 85
with the same gearing?  Thoughts?  Comments?

[hatzie]

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.

[zieg85]

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.

Well my 85 C20 bone stock 454 4 speed 3.21 gears does a decent job that is why I thought the 6.0L in the 2500HD would actually be a little peppier with the same rear end gear.  I am getting 13-14 in the winter and slightly under 16 in the summer.  Mine is a work truck so no AC.  My thoughts are lower rpm at highway speeds would help my fuel economy some and if I needed to tow my car trailer I wouldn't use 5th gear.  I am running LT265/75R16 and the speedometer is 2 mph off at 60.  60 on the speedometer is 62 on the GPS. 

[hatzie]

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 when you graph Y=MPG and X=CID.

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.

[zieg85]

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.

Thanks for the reply it is very informative.  My 85 has been parked for a while so I must have forgotten the torque difference which was no problem doing anything with that high gear.  Low was actually useful getting loads moving.

[Irish_Alley]

to add a little more info i know with the cummins 3.55 was pretty much standard gearing and they make a lot more tq down low.

[hatzie]

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.

[zieg85]

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.

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.

[hatzie]

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.

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.

I still own a 2000 GMC with the 6.5L and a 2005 VW Jetta TDI.  I'll never buy another diesel. 

The 2000-2002 3/4ton GMT800 trucks are darn nice rigs that don't suffer from GM decontenting them like the 03-07 rigs.  I like my squares and my GMT400 is a nice truck but the T800 is a nicer daily driver.
The 6.0 is a dead reliable engine with power on-par with the 400SBC.  Pair that with the NV4500 and you won't have much maintenance outside of  filters, fluids, brakes, spark plugs/wires, and tires for a good long time. 
It has IFS so you get to do wheel bearings and A-Arm bushings around 125,000 miles.  You can and should grease the new ones through the ABS sensor hole.  There's a tool for doing this.  The guys that do get 300,000 miles or more out of a quality bearing cartridge.
Some folks complain about the rear disc brakes but they also drive around with coal black brake fluid instead of flushing it out with fresh every 2 years or so.
My clutches usually go 150,000 or more miles and it's not the major job that rebuilding the 4L80E slushbox will be.
Your truck still has cabin air filters and an actual fuel filter on the LH frame rail.  I had to install them on my 2005.  If you haven't replaced the pair of cabin air filters yet I would recommend having a vacuum handy.  Usually they are the original filthy nasty pair of cabin filters because nobody changes them. They're side by side...  you pull one out and then slide the other to the narrow hole and pull it out.

[zieg85]

[/quote]
.
Your truck still has cabin air filters and an actual fuel filter on the LH frame rail.  I had to install them on my 2005.  If you haven't replaced the pair of cabin air filters yet I would recommend having a vacuum handy.  Usually they are the original filthy nasty pair of cabin filters because nobody changes them. They're side by side...  you pull one out and then slide the other to the narrow hole and pull it out.
[/quote]

Thanks again, had no idea on the cabin filters, got to check into that.  Truck has 136K on it so I probably need to at least check into the control arms and wheel bearings.  I had the truck aligned when I got it around 125K and the front end was tight with the exception of the left inner tie rod which I had replaced.  The truck drives amazing and if I got 18 mpg I would totally be happy with it.  For a former service truck of a John Deere dealership it was maintained well.  Kind of lucky it is only a 2 wheel drive so it was mainly parked in the winter indoors.

[hatzie]

.
Your truck still has cabin air filters and an actual fuel filter on the LH frame rail.  I had to install them on my 2005.  If you haven't replaced the pair of cabin air filters yet I would recommend having a vacuum handy.  Usually they are the original filthy nasty pair of cabin filters because nobody changes them. They're side by side...  you pull one out and then slide the other to the narrow hole and pull it out.
[/quote]

Thanks again, had no idea on the cabin filters, got to check into that.  Truck has 136K on it so I probably need to at least check into the control arms and wheel bearings.  I had the truck aligned when I got it around 125K and the front end was tight with the exception of the left inner tie rod which I had replaced.  The truck drives amazing and if I got 18 mpg I would totally be happy with it.  For a former service truck of a John Deere dealership it was maintained well.  Kind of lucky it is only a 2 wheel drive so it was mainly parked in the winter indoors.
[/quote]

Red Squirrels and Mice don't like the flavor of the activated carbon filters so they stay out of the ducts...  They're usually only a few $ more.