Tugly- thanks for chiming in. The 4.88's with 35" tires will leave an effective ratio around 4.39. 4.30 is a desired gear for modular engines in the super duty platform.

 

Where will that put his RPMs on his common nemesis grade? What is the troublesome grade? 8% at 65 MPH?

 

Hey Tugly!

Thanks for joining the conversation. I haven't done the math or dialed in on any one area in particular. Just that it seems it could perform better. We are pretty close. I don't make it to Wenatchee often but we do head to Omak from time to time.

Appreciate the info for the shop. I'll reach out to them when time comes time to swap.

Thanks for the maths Bently_Coop!

Hey Tugly,

I don't know the grades over Sherman off hand. I will have to pay better attention next time over, which will likely be this weekend. I tried to look them up but didn't have any luck finding the info. What I can tell you is that the driving speed over Sherman changes often from 35MPH to 55MPH and there are a lot of curves. The constant speeding up and slowing down while making the drive over the pass just doesn't feel like the truck is performing optimally.

The best way I can describe it is that I can be cruising along just fine (without GVOD) and sometimes when I hit an incline or when I am trying to accelerate again after slowing down to navigate a hairpin turn, the truck will bog-down (for lack of a better term), the RPMs go way up but I don't feel that I'm getting the power or acceleration necessary to handedly overcome the climb, it's really working to get up the hill.

I don't know if any of this makes any sense?

 

Thanks for the compliment but I didn't do the math. WE3Zs aka Tom has shared it so many times I have it ingrained in my head. I am sure he has posted where the RPM's would be for gear specific.

 

Thanks Coop, My setup is 4.88 gears with 35.28" tires. I figured that out to be an effective 4.39 ratio. using my GPS to verify the speed and my Ultra-Gauge for the digital Tach I documented these figures.

50 MPH = 1720 RPMs
55 MPH = 1900 RPMs
60 MPH = 2055 RPMs
65 MPH = 2230 RPMs
70 MPH = 2408 RPMs
75 MPH = 2580 RPMs

I don't know the exact grades percentages but last week I was hammering it home from Charlotte NC up I-81 through the Blue Ridge mountains and was pulling the up grades at 73 MPH at 2500 RPMs. At that sweet spot the V-10 was feeling very strong and holding that speed in OD if I hit the start of the climb with good momentum. I was using the 89 Octane performance tune and was pulling the 11,000 lbs TT, 569 mile trip with moving average speed of 60.1 MPH and ended up with 8.2 MPG.

 

There is some good information in this thread. You gasser guys deal with a different power band than I do, but the math helps me to sort it out.

The reason I target the specific grades is because there are a few long ones near me that would eat my lunch when I had a 460 and a boat. Vantage Grade is a bad one... so much so that it has a name. If I were to drive that on a daily or weekly basis with a gasser (like I did with the 460), I would target my gearing to deal with that, then the other grades would pretty much fall into line.

This is not the vantage grade, but it gets one's attention:

 

Chad : " Gear Vendors Under/Overdrive " does this mean it has LOW as well as HIGH


Did you replace the front hubs to Manual Hubs I was curious what your gearing is like if you put the GV in overdrive & the T-case in LOW ( W/O the front end hubs locked)..


How fast are you trying the drive the pass.. OVER 50 mph


Looking at your SIG, I don't see a TUNER yet.. IT might clear things up for you. Better performance, BUT best of all you can firm up the Transmission & get your Speed-O in line again....

 

TUGLY : Is that cash flowing from the bazooka on your shoulder ?? I can't tell....

 

Hey Tugly!

I really appreciate all of your input/feedback. It's very helpful!

Hi harley4jcs,

The GVOD was put in by the PO. I don't really know a lot about it other than it's setup to engage at 55MPH unless I turn it off. I suppose I should do some more research on what all that thing can do!

I typically follow the speed limits 50-55MPH.

I do not have a tuner, yet. Adding 5Star is part of the plan. However, it's my understanding it usually makes more sense to make all of your mods/changes/upgrades, before tuning so they can dial everything in based on those mods/changes/upgrades.

 

I guess if your going to run a custom chip. I use Hypertech or Supertuner box programmers so I can change what I want when I want. I wait till I find them on E-bay for $50 to $75 & they do everything I want them to do. Look at Tom's post above, 4.88s make perfect since. He's pulling 11,000 pounds !! I pull 12K in the hill country (2000' ele) 4.30s on 37" tires so close to 3.73 final ratio. I get it's not a 5000' pass but I'm dragging 12,000 pounds behind me for petes sake. I forget what low on the T-case is limited to BUT with the overdrive engaged I'm sure 50 - 55 would not be a problem ( Others please confirm or deny ) BUT you just said it's auto or off. It would be interesting to see if it kicked in with the T-case in low. If the under/over really has an under that would be the ticket...

 

Low range is often regarded to have a max speed of 25mph if I remember correctly. Power and torque whizzing that gearset around faster than that isn't a great idea...

Chad, that GVOD should be splitting all the gears in your trans so end up with an 8-spd slushbox. The one I had on my Chevelle turned the TH400 in a 6-spd, with manual mode as an option for engagement via floor switch (optional push button's are available). How is your's setup? Unless I misunderstood your post, it seems like it only kicks on at 55? That thing should be capable of kicking on and off between each OEM ratio - especially since their website chart indicates it splits each OEM ratio.

 

Hey Matt,

The ugly stcker on the side says 8-Speed. I do recall reading that it can/will work between each. I just honestly don't really understand how it all works, hell I'm probably not even using it to it's full capabilities. I should really spend some time getting knowledgeable about it. I may scan in the booklet that came with it for folks interested in more info on the GVOD.

There is an auto and a manual option. The GVOD kicks in and the green OD indicator light comes on when set to auto, at 55 MPH. Otherwise, the floor switch is available to use if you choose to manual operation.

 

"Low range is often regarded to have a max speed of 25mph if I remember correctly. Power and torque whizzing that gearset around faster than that isn't a great idea..."


AHH Crap, I thought it was 50-55. I recons I was thinking of max (recommended) speed to hit the OTF 4x4 switch . Most the time when I'm in low, I put in 1st as well SO I'm not looking at the speed-o. I'm just trying to get the load up the drive

 

You'll feel it shifting through all the 'gears' if it's setup for the full splitter operation, soooo do you? If it's only kicking on at 55 it's definitely not being used to its full potential.

I would investigate and read up on some literature regarding its operation and how to set it up for the full range of its capabilities. If indeed it isn't currently setup properly right now I would see about doing so, then afterwards see how it performs. It may turn out that you won't need to spend money on upgrades afterall.

 

Maybe that thing can be reworked to be under driven like it says?

Time to call the manufacturer I would think. They have a good reputation. I bet their customer service will be great.