Some impressions: 48re vs NV5600

[Rod_Montana]

Some impressions: 48re vs NV5600/or G56 (post 9)

Just traded a 04. 5 Auto for a 05 6-speed.



Spent 30k+ in the earlier truck, my first CTD. Early on it seemed very impressive when rolling on the thottle to do a high-speed pass, but the longer I had it, the less inspiring it seemed to be. I don't think this was a maintenance issue, as that truck got top flight care. Might have been "familiarity" effect. I tended to drive it conservatively, as fuel prices soon went upside down relative to gasoline and it averaged about 17. 0 once break-in period was over (18-20k miles). The 48re always seemed to have a big dead spot from 1500-2000rpm, where nothing exciting happened. Much more than 1/4 throttle jumped it up to 2200-2300rpm, where mileage sucked and even there it was kind of ho-hum. Things got better around 2500rpm.



The 05 is a entirely different animal. First of all, it's getting an honest 18. 5mpg already (11k miles). The hand-calc exceeds what the overhead says but only by a little. 2nd and 3rd gear seem a little breathless. By that I mean, the truck starts to pull and then goes somewhat dead around 2000rpm. I'll confess to keeping my foot out of it, maybe 1/3-1/2 throttle. Feels like boost starts to come on and then immediately shuts off.



HOWEVER, do this is 4th and look out. 5th is even more impressive because the acceleration continues at the same rate and speed is really building. A charge from 1500rpm to 2500rpm in 4th or 5th is much more impressive than in the lower gears. And this is only half throttle. This truck seems far stronger than the 04. 5.



If we hadn't had two 04. 5 trucks, I would be tempted to think the one just traded had a problem. But the one we still have drives identically. Were there some changes in 05? I believed they were basically identical to the 04. 5 trucks.



Am I seeing defueling because of overboost in the lower gears of the 05? Overall, the 05 feels like it has about 50hp more motor. Very strange.

 

[klenger]

Your results witht the 05 are similar to how my 04. 5 NV5600 feels. Much better power in the higher gears. I have no idea why. As far as I know, there is no defueling in any gear with the manual. FWIW, the 05's are 610 torque vs 600 for the 04. 5's, so something is a bit different. Another thing to keep in mind is that the 48RE and NV4500 are geared differently.

 

[Ross]

What you seeing is the very nature of the Cummins turbo diesel (and all TDs). In the lower gears (both 6 spds & autos), you are not loading the engine enough to make big boost, plus you're not in the lower gears long enough for anything to happen, really. This is why the earlier autos with the slushy torque converters seem like such pigs; they wouldn't ever "positively" couple the load to the engine. Just a change to a tighter TC will really wake up an auto, but you are still dealing with the lack of load issue in the lower gears, for both transmission types. That's why all dyno runs are done in a high gear (like direct). It's my belief (some disagreement here), that the higher rear end ratios (like the old 3. 54s) seem to accelerate a load better than the deeper 4:10s. At least this seems true for all but the heaviest (+15,000 pounds) weights. With the lower gears, there's less mechanical advantage by the gearing, so the load on the motor is greater, so more fuel is needed, so more boost is built, so more fuel can be burned, so more exhaust gases are made, so more boost is built, so more fuel can be burned,... ..... on and on we go!!! Ain't it cool?

 

[klenger]

Thast seems to be a good explanation.

 

[Alan Reagan]

Another part of the consideration is that the manual is much more efficient. It doesn't have the 10-20% loss of efficiency.



I had an 01 six speed that felt a lot stronger than my 05 auto.

 

[JCleary]

Just traded a 04. 5 Auto for a 05 6-speed.



Spent 30k+ in the earlier truck, my first CTD. Early on it seemed very impressive when rolling on the thottle to do a high-speed pass, but the longer I had it, the less inspiring it seemed to be. I don't think this was a maintenance issue, as that truck got top flight care. Might have been "familiarity" effect. I tended to drive it conservatively, as fuel prices soon went upside down relative to gasoline and it averaged about 17. 0 once break-in period was over (18-20k miles). The 48re always seemed to have a big dead spot from 1500-2000rpm, where nothing exciting happened. Much more than 1/4 throttle jumped it up to 2200-2300rpm, where mileage sucked and even there it was kind of ho-hum. Things got better around 2500rpm.



The 05 is a entirely different animal. First of all, it's getting an honest 18. 5mpg already (11k miles). The hand-calc exceeds what the overhead says but only by a little. 2nd and 3rd gear seem a little breathless. By that I mean, the truck starts to pull and then goes somewhat dead around 2000rpm. I'll confess to keeping my foot out of it, maybe 1/3-1/2 throttle. Feels like boost starts to come on and then immediately shuts off.



HOWEVER, do this is 4th and look out. 5th is even more impressive because the acceleration continues at the same rate and speed is really building. A charge from 1500rpm to 2500rpm in 4th or 5th is much more impressive than in the lower gears. And this is only half throttle. This truck seems far stronger than the 04. 5.



If we hadn't had two 04. 5 trucks, I would be tempted to think the one just traded had a problem. But the one we still have drives identically. Were there some changes in 05? I believed they were basically identical to the 04. 5 trucks.



Am I seeing defueling because of overboost in the lower gears of the 05? Overall, the 05 feels like it has about 50hp more motor. Very strange.

The way the throttle seems to work with the manual trans is that if you give it partial throttle, it will accelerate hard until you reach the point where that particular throttle position maintains a certain rpm level. If you keep rolling into the throttle the truck will keep on accelerating. Same if you mat the pedal. This is exaggerated with any fueling box you may have. In fact, with my TST Early Twins flash, with anything over about levels 4x3 or so my turbo will bark without me lifting the throttle. I just have to push the throttle 1/2 way, then wait for the ECM to pull back fueling, and WOOF!



No problems if I anticipate it and either feed more throttle, or lift to activate my BOV.



For the most efficient high-speed shifting, I'd recommend lifting at 3k rpm to shift. No need to rev it out.



Around town I'd recommend shifting at 1800-2000rpm to keep your fuel mileage up.

 

[Prairie Dog]

As far as I know, there is no defueling in any gear with the manual.

Actually there is defueling in both 1st and 2nd from what I've read. A good fueling box pretty much makes up for it though



Scotty

 

[HBarlow]

What you seeing is the very nature of the Cummins turbo diesel (and all TDs). In the lower gears (both 6 spds & autos), you are not loading the engine enough to make big boost, plus you're not in the lower gears long enough for anything to happen, really. This is why the earlier autos with the slushy torque converters seem like such pigs; they wouldn't ever "positively" couple the load to the engine. Just a change to a tighter TC will really wake up an auto, but you are still dealing with the lack of load issue in the lower gears, for both transmission types. That's why all dyno runs are done in a high gear (like direct). It's my belief (some disagreement here), that the higher rear end ratios (like the old 3. 54s) seem to accelerate a load better than the deeper 4:10s. At least this seems true for all but the heaviest (+15,000 pounds) weights. With the lower gears, there's less mechanical advantage by the gearing, so the load on the motor is greater, so more fuel is needed, so more boost is built, so more fuel can be burned, so more exhaust gases are made, so more boost is built, so more fuel can be burned,... ..... on and on we go!!! Ain't it cool?

Your explanation makes a lot of sense. I don't have any experience (yet) with automatic transmissions behind the Cummins engine but your description matches my experience with my current truck.



Harvey

 

[klenger]

I'd love to hear an honest 1st hand comparison of the NV5600 vs G56 as well stated as this one and w/o all the emotion in the previous G56 threads.

 

[Rod_Montana]

G56 vs NV5600? I can to that one also. It was my intention to move to an 06 truck with the 6-speed. There is certainly a better financial incentive to go to a new truck, rather than an 05 with 10k on it. Like 0% financing for one. So I started driving a 06 with the G56 first.



First impressions of the G56:



Like the clutch engagement - better than my 05 with the NV5600. Smooth and progressive from about mid-pedal out. The clutch on the NV5600 dumps in a bit too late for my liking, making it more difficult to do the silky-smooth transitions between gears. I'm working on it, and after 1k miles I'm getting better, but with the G56 it was good from the get-go.



In town empty. Start in 2nd as with the NV5600, or third. (Don't try that with the NV5600). 3-4 shift in stop light to stop light work. NV5600 needs 2-3-4. Or do 2-4 with the G56. The gearing empty allows this. Not so the Nv5600.



On in the burbs and on the highway is where the G56 fell apart for me. 1950rpm sweet spot occurs at 60mph. On the NV5600 its more like 66 and 69 on the 48re. 33x12. 50 tires give me 69 on my NV5600.



For those who want to tow big, I have to believe the G56 would about perfect. Gears are nice and close down low and you have plenty of HP and torque on tap at somewhat reduced highway speeds of 58-65mph.



For those who want to tow small, or not at all, there should have been another gear ratio offered. Say like 3. 54.



On a stock truck, those are the primary decision factors. For those who want performance mods (bombs, etc), a whole lot of reading on this forum is probably in order.