Update on 0.8555 ratio for USG Dual Range Overdrive

[pdolan]

For those of you who aren't aware, we have had a project going at the Ford site to get a gearset for the USGear Dual Range Auxiliary OD that will split the ZF6 evenly in top two gears. It just so happens that it will be the perfect split for the NV4500 and 5600 as well. What do I mean? Here are some NV5600 steps with various overdrive ratios, expressed in percent of step UP to the next gear. Tell me which spacing you would find useful:



gear step up with 0. 78 0. 8 0. 8555



3rd to 3OD 28% 25% 17%

3OD to 4rth 14% 17% 25%

4rth to 4OD 28% 25% 17%

4OD to 5th 8% 11% 19%

5th to 5OD 28% 25% 17%

5OD to 6th 7% 10% 17%

6th to 6OD 28% 25% 17%



(The ZF6 does NOT split this nicely!)



The two existing overdrive boxes do give you "twice as many gears", but as you can see, the steps are so small that in most cases, you really don't gain anything by splitting anything but third, so 4-5 and 5-6 are not splittable - the very ones you NEED when towing. Looking at the steps with 0. 8555, you can see why it makes a lot of sense. A 2,500 rpm shift will drop you back to 2,140 (OK, 2,100 because you will take some time, even frantically climbing a 7% grade).



After much time, we got a design study that figured out how to cut the gears without totally re-designing the box, and they considred making us some experimental sets. Now the production order is in for prototyping, and USG will do some in-house R&D. If the design works in the real world, this could become a product before too long. Will keep you posted.



Pat

 

[Turbo Horseman]

Not quite sure what the %'s mean and why 17% is better than 28%.



Does it mean something like 3rd is 100 (base number for argument purposes) that 3rd OD is 117, 4th is 134, 4th OD is 151, 5th is 168 and 5th OD is 185 (I have a 5 speed) resulting in uniform steps or spacing between gears?



Or is the gearing only taking you (consistently) 17% of the way between gearing steps?



Is it possible to post the actual numbers?

 

[RustyJC]

Looks like the 0. 8555 ratio would drop 70 MPH RPM's for those of us with 4. 10's from ~2350 RPM back to ~2010 RPM - almost identical to those trucks running 3. 54's. (4. 10 x 0. 8555 = 3. 51 effective rear axle ratio). It would be nice to have a usable split between 5th and 6th as well when towing as heavy as we do with our 5th wheel (21,180 GCW versus 21,500 GCWR).



Rusty

 

[onestackdram]

Being the moron I am with all those numbers listed, I can say that if Rusty is right, I am extremely interested. I love my 4:10's for towing POWER but absoluetly HATE them for traveling when empty 70 MPH = 2450 RPM's for me with NV4500. But if that split would me 70 MPH = (approx. ) 2000-2100 RPM's I would buy one in a heart beat. Hell I would be willing to be a guinea pig for the deal. I can give reports on towing (fairly regularly pulling 30K on 48' gooseneck) (dont worry not factory springs and frame reinforced for weight) and could give reports on LONG rides up and down interstates and in city when empty.

 

[pdolan]

Horseman:



Holly mackerel, Batman, my post lost its columns!! Sorry guys.



The first set of numbers in the series is the % steps UP to the next gear for 0. 78 (GV) , the next 0. 8 (USG) and the third column is the steps between gears for 0. 8555.



To get the rev drop, take your shift speed and divide by 1. xx.

i. e. , a 2500 rpm shift at 17% will bring you into the next gear at 2500/1. 17 = 2140.



Why is 17% better than 28%? Because a 28% upshift is followed by a 7 or 8% shift, which is not of any use (same revs for all intense and purposes). In other words, the gear doesn't split, you gain no useful ratio except for one OD above top. If you want to get right down to it, it is free horsepower. When you plot the horsepower curve, you will see that shifting around its peak means you have a LOT more power available to the driveshaft during times when lower revs would have cut you back quite a bit. No good for bragging rights on dyno night, but worth its weight in nitrous on the way up a big hill at high gross.



What is unique about the NV5600 is that it will split all of the gears from 3rd on up evenly with 0. 85, which other boxes won't do. This means that especially 4,5,6 open up to 6 full, even steps.



Onestack:



I tow up at your weights with a 450 Powerjoke, which is where and why this project began. It took a long time for the marketing guys at USG to figure out why I was so hot on this, but the engineering guys jumped right in and came up with some possible ways to do it (which is what will be on test next month). Now the marketing guys are heavy duty on board and we are moving rapidly forward.





Pat

 

[Turbo Horseman]

A great difference in shifting from 28 down to 7 or 8%, no doubt. So this means 4th to 4th O/D is 17% and then the split from 4th O/D to 5th is 17%? This I understand.



Iffin that's so... then... hey... I'm glad I haven't purchased a splitter yet. Now I'm thinking about getting one more... wanting to hear more... how many pennies... when... when... damn... it's happening again... must bomb soon.

 

[pdolan]

It means the steps UP from 4rth are 17%, 19%, 17%, 17% and 17% to 4OD, 5, 5DO, 6 and 6OD respectively.



When? As soon as USG is done testing. How much? Should be witing a couple of hundred of regular price (see their website).

 

[BigDan]

I dont tow anything so heavy that I actually need in-between gears on my NV5600. Its already a really close ratio especally with 4. 10's. The only benifit I see, is haveing a 6th OD to increase crusing RPM's, so with that in mind I would want the gear set which would allow the lowest RMP drop.

 

[livetodrive]

Has anyone considered a taller ratio for the auxiliary transmission? My priority is to drop engine speed when running empty on the highway. The 6-speed seems to have pretty good ratios from the factory (except for the short overdrive).



The standard US Gear is 0. 80 ratio overdrive. I'm thinking something like 0. 67 (or so) to drop cruising RPM while still allowing gear splitting. Shift pattern would be ... 4th, 3rd-over, 5th, 4th-over, 6th, 5th-over, and a final big jump to 6th-over to be used only when running light on the highway. It would take a bit of getting used to, but should not be a problem for a competent driver.



I've about given up on the auxiliaries due to the limited benefit of only 0. 8 overdrive. If there's enough interest, maybe we could get US Gear to offer a higher (numerically lower) ratio (as they already have in their hot-rod version, but it can't handle our torque).



Wadda y'all think?

 

[onestackdram]

Well I dont know about all that shift pattern stuff, but I am up the same tree as "livetodrive". I dont really have a need for inbetween gears with my 4:10's even with my 5 speed. I am pretty happy with the split already there. My concerns and or needs for this would be a split between 4th and 5th simply to move down the interstates at a safe speed in 4th with a load. And MOST importantly I need and WANT something behind 5th so that when I am empty I can cruise down the road at comfortable speed, both in terms of MPH and RPM's. Not the screaming banchee she is right now at 70-75. What I would almost like is something that would make the FINAL drive think the rear end is only a 3:54 or Taller. And then in a shift I am back in towing gears. I dont know if that rant made sense or not, but thats how a moron thinks... LOL



Russell

 

[pdolan]

Yeah, these are two very different reasons for having an auxiliary. Only the serious, heavy tow types need the 0. 8555, since the split does make the whole thing easier to get up a hill. I agree that there needs to be a super-tall ratio for those who want to run down the road empty. Rather than shifting at 6th, you would just leave it in OD all of the way through the gears when empty, and out of OD when towing.



Pat

 

[rubberneck]

5th over would be sweet for those long hills where i just cant pull 6th due to egt or h2o temps, and 5th seems to be zinging the motor just a little more than i would like. I gross at 22k and i think this thing would be great. 6th over would be sweet on the flats when empty, i am very interested. One question, how much torque will these things handle??,

 

[onestackdram]

Yeah, these are two very different reasons for having an auxiliary. Only the serious, heavy tow types need the 0. 8555, since the split does make the whole thing easier to get up a hill. I agree that there needs to be a super-tall ratio for those who want to run down the road empty. Rather than shifting at 6th, you would just leave it in OD all of the way through the gears when empty, and out of OD when towing

EXACTLY



Russell

 

[Turbo Horseman]

Towing season is coming for me - runs May to October.



I would like to have a 4O/D so I don't have to do about 110 km (68 mph) to avoid that "bogging" feeling in 5th. The roads up here don't tow well at that speed. So you have to go slower, constantly shifting 4th and 5th.



The O/D would allow a lower speed and provide fuel economy since the engine wouldn't be up at 2375 rpm (I think) at 100 km (62 mph) which is the maximum speed limit in these parts. Could stay in O/D for most of a trip.



Running empty, use 5O/D. Drop the rpms and let her rip... yeeha!



Oo.

 

[pdolan]

Rubberneck:



They rate them by gross weight, and I think the RECOMMENDED max is 30k. There is a torque limit, but I am not sure what it is. Since they have no prohibition about using the OD box in the lower gears, it will handle over 2,500 lb/ft without breaking. The limit in towing ranges is not torque, but heat.



Horseman:



Your needs are exactly where this kind of split is needed, but not yet available. Hang in there and we should get our box this summer. I will keep you advised as testing carries on.



Pat

 

[Turbo Horseman]

Ahhh... but I want it now That's too long, I need instant gratification... stupid R&D time lines etc.

 

[rubberneck]

pdolan, thanks, I will have to check into the ratings. I guess my biggest concern is that i have heard stories of the various OD units grenading under high HP/ abuse situations. These may be no more than just urban legends, but i would hate to introduce a weak link. You see i pull at about 22-23k gross, but i also like to hot rod and get in the occasional stop light to stop light fun. I would hate to drop the clutch to a loud bang if you know what i mean. currently i am at about 425-450 rwhp with my set up, so my guess is 900-1000 ft/lb torque, take into account the gear multiplication through the trans, and i think i may be a tad over 2500ft/lbs at the OD unit. I really like what you have going on here though. I have the 6 speed, and the more i think about it, 5th over might even be super sweet when pulling on the flats for me. I have the 3. 54 rear end with 33" tires. I will definitely be keeping an eye on this, keep us posted.

 

[livetodrive]

Has anyone approached Gear Vendors about developing a different (e. g. , taller) overdrive ratio? Their unit looks like a better fit in the driveline tunnel on the 2003s.



Drive Safe!