Rear-End Gear Ratios

[Rawze]

(08-09-2017 )ZeroNthedark Wrote:  This is a question I've been wanting to ask for a long time, but not known how to bring it up...

My daily driver is a 2005 Pete 379 tri-axle dump truck(so a brick, basically). It has 425 steers and 11R-24.5 drives with 4:10 gears pushed by a 475 CM 870 and a manual 18-spd. Now I realize Hammerhead has had work done to his, and mine is in serious need of help, so we'll discount that for a minute, but why does it seem that if I drive 70-ish, at around 1600 RPM all day, my mileage appears better than if I go around 55-62, which is either 1400 in top gear or 1550 down a half gear? I usually try to keep my Boost under 30, mostly around 20, and Pyro hovers around 800 on tall hills, sometimes 850. This is in Western PA, so it's pretty much you're going up a hill or coming down. Very little flat ground on my runs except for I-76 between the 13 and 75. Which I don't get very often.

Sorry if I got long-winded or hijacked the thread, just looked like a good time to ask.

BTW- Best mileage I've managed is low 6's. Usually around 5.5.

Poorly reading/old sensors can cause that. Sensors that are reading wrong or have their readings dulled out because they are old or are clogged will cause efficiency problems that will make a truck seem it does better when driven hard vs light. It is a false sense of empowerment though, and the vehicle is suffering all losses all the way around when it comes right down to it. I have seen guys complain they get 5 mpg at 70-mph loaded,.. then 5 mpg empty or bobtail and going 60. This is because of engine sensor and other problems, and has nothing to do with speeds and momentum. When they update/replace the engine sensors as they get old, many times it fixes the problem, and suddenly they see 8-10 mpg empty and 6+ mpg at 68-70.

Leaky CAC or other intake circuits can cause one to get better (or the same) mileage at higher speeds. This is because you generally use less boost pressure, and less often at higher speeds and the leak is not as bad. Even so,.. fixing the leaks will improve it at both higher and lower speeds. Ensure you don't have any leaks by pressure testing the entire engine, not just the CAC.
Reference: http://rawze.com/forums/showthread.php?t...07#pid8307


Next,... Lots of guys complain about not gaining much by slowing down if their truck is not de-mandated with very good programming to prevent the axillary, off-road, and egr-valve un-plugged back-up emissions managers from kicking back in. Most guys who have 870's and unplug that egr valve or that egr temp sensor never bother to get it properly re-programmed. The result is that the engine is fighting the back-up emissions and they get only about 32-33 psi of boost as well. Still yet, even many guys who are getting re-programming, for the the 870, the bulk of guys programming them have no clue how to turn off all those back-up emissions that kick in when you do unplug things. 870 is one of the most difficult engines to get that stuff turned off properly, some of it is not even in the program but only in the ram of the ecu. You could very well be fighting those things as much as anything else depending on who might have programmed it.

Next...

If your truck is not DE-mandated at all, that will often cause a lot of "see no gains when slowing down". The harder you drive, the more lenient the EGR is so it can make that power, and the lighter on the pedal, the more restrictive it becomes. Personally, I think that is total BS and is geared more for making the oil companies more money, and has nothing much to do with the environment. It ensures you spend more money on fuel than you should be no matter how you drive and is counter-productive to maximizing profit. My own truck would not peak more than 6.8 mpg when I first got it no matter how slow I drove it. I fixed that s#it right away the first time it got custom tuned.


Aside from that,.. With a de-mandated, well tuned, healthy truck + all sensors reading correctly and not dulled out like the boost pressure and exhaust pressure sensors, sometimes it is a matter of how you are driving it.

We drive in those same hills a lot, and even at 80,000 lbs gross with loads of Nesle Water headed for Wallmart DC's, we don't really loose fuel mileage. At 58~ish We still get in the ghig 7's, sometimes even low 8's. Here is what we figured out running in those areas...

Let the weight work for you not against you. A lot of guys who slow down, push the truck harder for longer at lower speeds because they are used to going faster and so they are trying to hold more constant speeds in terrain where you simply can't.

What we do to maximize our momentum is we use a lot of OOG (Out Of Gear) and are letting it get +5 (or sometimes more if traffic is moving fast or it prevails) over the speed limits, then letting it come to a crawl as it crests on every one of those hills. We crest one hill, drop it off in neutral, and only touch the brakes a tiny bit towards the bottom to keep form speeding too much,.. then instead of grabbing the top gear when it slows down,.. we grab one gear less at 1700 rpm, use very little boost, let it slow down a bit as it crests the next hill. We are usually only going about 45-50 or so as it crests each of those hills, and let it roll again. Purposefully cresting at a lower speed at the top allows for it to roll for longer without it going as fast at the bottom. In other words,.. we work the living s#it out of it between 9'th and 10th and neutral (we have a 10 speed tranny) in those hills and we don't loose any fuel mileage because we are heavy.

Driving style plays a big roll in what your efficiency is when you are in terrain that has a lot of variation.

===

I have met a lot of guys who have exactly this issue, and claim those things like going faster is better. They had the problem for so long, that they will just argue with you and tell you that getting a "running start" up hills is more efficient and all sorts of other excuses. -- Install boost and pyro gauges with the pyro gauge on the OUTSIDE of the manifold and not inside the exhaust piping, drive by them and do things to lower the pyro as much as possible at every speed, Fix all the problems,.. Fix the engine so that it is not sucking twice as much egr when you slow down or run lower rpm. If it is de-mandate, in the case of the 870,.. have Gearhead ensure all the aux/backup emissions fall-backs are axed properly. Fix and replace old sensors, and drive it to maximize momentum instead of keeping steady speeds. Drivers who do this always call me up in a few weeks and say -- "DAMMMN,.. I NEVER KNEW".


- I know there are always some truck owners who are too damn stubborn to figure it all out. They simply piss and argue and justify going faster instead of solving their issues and figuring out why when they slow down, they do not see any of the gains they should be getting. There are always gains for slowing down and using less overall energy. Fuel = energy, simple at that. there is no such thing as using less energy at higher speeds simply because you are in terrain that is hilly.

Here is some posts form the old forum where someone had the typical bad programming/bad delete from a big name tuning company and the back-up emissions were still active and holding the efficiency back all the time. They ended up turning the power down while they were at it because the bad delete had the power up at harmful levels too ....

======================================
re-posted form old forum...
======================================
- This guy has one of the worst situations for driving a truck and trying to get fuel mileage gains that I have ever come across. Basically he drives daily, west of Colorado across I-70 copper mountain + veil pass (One of the toughest places in the USA to have a daily run for a heavy truck)...

(01-23-2015 )vtbhorvath Wrote:  With the help of Rawze and Gearhead, I feel like I have a new truck. Sounds, runs and drives totally different. My numbers & settings are where they need to be. Tomorrow will be the first true test, as I make my usual Rocky Mountains run. Big thanks again both of you for assisting me when I needed it the most.

Give us some feedback here on the forum. I am sure others are as curious as I am for a truck that has to be tortured by veil pass and copper mountain 5 days a week. If it needs some adjustment or further custom tuning, let me know as well. The Tune I sent gearhead today is the one I use for most trucks that come here and not so much for that type of driving. He told me he was putting it in your truck. It likely needs some adjusting for that type of torture/use at higher power levels.
...
....

(01-27-2015 )vtbhorvath Wrote:  UPDATES for my Upgrade:
The truck runs great. 1st day into the mountains I got a little scared at the first hill (Lookout Mountain) because I had to downshift one more than I am used to doing (same weight as always). Boost was kept around 25, manifold temp was no more than 600F, by the time I got to Vail, I crossed over 3-4 hills, my total trip took approx. 10 minutes longer than I have been used to. The readout in the truck about MPG looked very promising. Like always, I never went over 60 MPH. By the time I got to Grand Junction the MPG readout displayed 7.5 MPG, and my fuel gauge didn't move too much. On my way back I had approx. 15K LBS in the box, so I was light and I'm doing 62MPH and fueled up in Denver. True MPG was 6.7
...
The downside is my HP decreased, but MPG increased by at least 1/2 MPG (using winter blend fuel).

Inline still doesn't communicate with the ECM with the Deutch plug. I'm on good terms with the company who I lease to and I asked for new wires and a new QUALCOMM, and I installed it at home. I made sure all the wires were short and twisted together the ones that need to be

...

The next 2 runs, the truck ran as described above. MPG is also about the same. Yesterday, on my way there I went approx. 58 MPH (because the load was heavier) for about 50 miles past Vail, then increased speed to 60 and the MPG went up another 0.2. I am very happy about all of this. In the summertime the results should be even better.

......

Rawze Wrote:As far as power goes, that can be adjusted, I think gearhead told me that he set it back to stock before doing the mod to get rid of the bad d'lete.

Remember, the standard MM overlay is typically set for more fuel mileage, not more power. Your power fell off because it got set back to factory levels even before the mm overlay was put in. It can be adjusted back though,... so,... Now, you need to make a decision,... more power and less fuel mileage,... or more fuel mileage and less power. It is set for running as efficiently as it can now, so it is NOT a matter of more power without sacrificing some fuel mileage. From what you say,... 1/2 mile to the gallon is BIG considering where you are driving. 10 minutes is not worth more power if you ask me, because you will likely make/save a LOT more money for that 10 extra minutes. Do the math and you will see.

Your situation is a very nice one to be in for testing this stuff. Manifold temps sound a bit on the low side for your situation though. Injection timing timing offset should be lowered to bring EGTs up a notch. 600 is a bit "cold" even for those bigger CAC and front end you have. It should also gain some torque and efficiency when re-adjusted. Do that and let me know. I would think that would help more than actually putting more raw power in it. Optimally, you should do this until you get to around 750 - 800 degrees F (max 900) in a hard pull on the pyro without having to worry about the turbo. The engine will be running in a safer zone at those high usage levels when set with 800-900~ish peak for protecting the cylinders.

I have driven those same mountains several times myself while adjusting injection timing on the fly. If gearhead put the MM in it as is (I think he did), then it is set for overall best for your average terrain (all 48 states per say),... but not so much for constant,dedicated mountains, hard pulling like you are doing ... It would be best to back the timing off a few degrees and let it get a little hotter. I did this for a construction truck once before that climbs a mountain all day with the same good results. Dialing things in properly for longevity and use provides the best results.

In the end, I don't think it will gain in fuel mileage if you turn up the power though ... It may become a trade-off of delivery time vs higher fuel costs.

For rare occasions and testing like this, I don't mind using remote desktop for, to help and teach you how to tweak on it yourself a bit so you can find those settings on your own. Remember though, all risk is yours. All I ask in return is that you share your results with others so everyone can benefit. In the end, there is no replacement for experience and shared knowledge.

.....

(01-28-2015 )vtbhorvath Wrote:  I will run the truck the way it is for now. Although I lost power, I believe that more $$ stays in my wallet this way. It is funny, I used to lead the way up the hills, and now I feel like I'm driving an old Swift FLD120. I drove one for a year.

I want to learn every day, and I do learn every day. I don't know how we could fine-tune on the fly, because I drive at night and phone reception goes in and out at times. If this can be done while bobtailing and on flat surface, in less traffic, then possibly.
Thanks for the good advice and feedback. Keep in touch

...

(01-29-2015 )Rawze Wrote:  It can be set to give just as much power as it did before, if not more. That is not very difficult to achieve,... but its like you said, and I tell everyone.

Do you want your ego fatter?,... or your wallet?,...

Me., I prefer the Wallet,... I will let my ego be satisfied by telling everyone how much more fuel I saved instead.

...

(01-29-2015 )vtbhorvath Wrote:  past 2 weeks mpg was 6.13,now 6.67, meaning saved circa 36 gallon fuel I'm pretty happy, "I prefer the Wallet".

======================================

So,.... Slowing down a bit, better programming + a bit less power = more money in the pocket at the end of the day instead of screaming up the hills. That was back in the M-M-1 days, hopefully he has had/done some updates to his programming along the way as the latest MM version "U" for 871 is much better.