I think you guys might find this neat. Basically you enter all but the g/kWh initially, based on your data plate. For instance, my engine says 215hp, 2600RPM, 103mm3... The spreadsheet is saved with my specs so you can see where they are. The fuel density should be left alone as thats the average density of diesel fuel, though I have it unlocked if you happen to know something about your fuel that I don't. You can see it calculates the g/kWh...This is the engine efficiency! Once you know it, copy 3 or 4 decimal places worth into the cell next to it. Once that is done, you can mess with all the rest and treat the g/kWh and fuel density as static variables. I added the MPG and MPH for the heck of it so you can see what you would be getting. There isn't much error checking on this as I'm busy with other crap so just use a little common sense as in don't leave more than one variable blank and don't fill them all in. I'll try and build it in later. If you are just wanting to mess with it (without looking at your data plate) just put 250 in for g/kWh as that is about the average of all the trucks. Oh and password to unlock is dodge as usual.

Engine Efficiency.xls

I was playing today on I-84 driving 73 mph (2200 rpms) and noticed my rail pressure was holding ±16,400 most of the time. So I cam back and looked at my tune, and some other data and I figure I was burning 28-30 mm3 on the main and 4.4-4.5mm3 on the pilot. All that comes back to ±21 mpg thanks to ISX's calculator. While I don't know how long it would hold over 20 mpg it sure was efficient today. I also played with the efficiency calculator, which is no where near scientific but... On several dyno's I had a 15% drivetrain loss on stock tuning. Last fall I dyno'd 369 rwhp (uncorrected) at 2900 rpms. That was a 8mm3 increase over stock (stock limits to 132, but the tables go to 140 and I was running the full 140mm3). So from timing and 8mm3 I picked up ~110 crank hp. Based on the calculator I went from 35.37% efficient to 44.6% efficient. Thank you EPA based timing. I know it's not very scientific, but it seems legit.

I was playing today on I-84 driving 73 mph (2200 rpms) and noticed my rail pressure was holding ±16,400 most of the time. So I cam back and looked at my tune, and some other data and I figure I was burning 28-30 mm3 on the main and 4.4-4.5mm3 on the pilot. All that comes back to ±21 mpg thanks to ISX's calculator. While I don't know how long it would hold over 20 mpg it sure was efficient today. I also played with the efficiency calculator, which is no where near scientific but... On several dyno's I had a 15% drivetrain loss on stock tuning. Last fall I dyno'd 369 rwhp (uncorrected) at 2900 rpms. That was a 8mm3 increase over stock (stock limits to 132, but the tables go to 140 and I was running the full 140mm3). So from timing and 8mm3 I picked up ~110 crank hp. Based on the calculator I went from 35.37% efficient to 44.6% efficient. Thank you EPA based timing. I know it's not very scientific, but it seems legit.

Learn to drive by your RP gauge if'n you want to maximize mileage. Keep RP as high as possible.

Learn to drive by your RP gauge if'n you want to maximize mileage. Keep RP as high as possible.

Most of us that are doing extensive testing and tuning would disagree with you. Increase pressure puts unneeded parasitic drag on the motor, and lowering pressure has been proven by multiple people to increase mileage. Once I got the timing corrected for the 3-5K lower psi at cruise my mileage went up. Increased pressure for mileage is a myth, that many have proven wrong.

What is the rail pressure based on and which way does it go according to the factors? If it uses timing does it go up as timing advances?....

Rail pressure has it's own command table, you can set it independent of timing.

Ok soooo based on engine load and RPM??

Ok soooo based on engine load and RPM??

Yes. Based off several parameters... I would imagine, in the R&D labs, based off everything from load to variable cam timing. Higher pressure through the same sized orifice effects droplet size and spray pattern. I ran into a pHd student the other day and discussed a bit. In theory, higher pressure means smaller droplet size and a faster burn of the fuel charge. However, the chamber and how the flame front progresses through the chamber is a tough thing to predict. So in the end, we tune the fuel maps for best performance since we can't totally model all the flows and transient thermodynamics & heat transfer involved in the combustion process. Slower burn is okay, especially at lower RPM and may make a more even combustion chamber temperature. However, at higher RPM things may be different. Older work... the new stuff in the next year or two should be cool. They are using an electric injector now, not the old poppet injectors. http://inside.mines.edu/~tparker/Diesel%20Spray%20Movies/ILASS%202003.pdf

Ok soooo based on engine load and RPM??

Yes as CSM said. Those are the two labels on the pressure table. Along with what CSM said the higher pressure has a much shorter ignition delay, and looking at the OEM timing and rail pressure tables for a 04.5-07 it's no wonder they have timing rattle. OEM is lots of timing and combined with the pressure down low, and really the motor doesn't like it (but the EPA might). I have generally lowered my pressure for nearly all of the cruise table and have a smoother, quieter and more fuel efficient cruise region, thou I cannot comment on what it may have done for the NOx or other things. While increased atomization can provide for a better burn, the hp required to increase the pressure from 16K to 19K seems to be greater than the hp gain from better atomization. As load increases we obviously are injecting more fuel, as pressure increases the time required to inject "x" fuel decreases and that means a shorter injection delay, less timing required, and a better burn. Those things are great at higher loads, but at low loads that can lead to increases pressure BTDC, timing rattle, and lower efficiency. Thru tuning I have also noticed that decreased pressure really increases turbo spool from the longer burn. For me personally I am running 5° to 9° less timing than stock between 1000 and 1400 rpms at low load and my pressure is fairly close to stock until 1550 rpms. What that timing decrease has done is increase spool, increase response, and decrease noise (my non-mechanical mom commented on how quiet my truck is compared to my dad's 06 with a Smarty Jr). There are places on my pressure map where I am 5660 psi lower than stock, and places where I am 4784 psi over stock and that is all within the OEM 23,206 limits. My pressure map is a continual increase from idle to WOT. If rpms and/or load are increasing so is rail pressure. That's not the case on the stock map.

I have a few more minutes to expand on my previous post...

So looking at stock vs my current setup. I'll use 1800 rpms (60 mph), 2000 rpms (67 mph) and 2200 rpms (73 mph). The mpg data is based off of ISX's calculator. The pilot is included but the post is not, there is a small 2mm3 post for the 1800 and 2000 rpm rows for stock, but not UDC. Stock does not use a post at 2200 rpms.

20mm3 is typically used for slight down hill at cruise speed, 30-45mm3 is normal flat cruise range. As you go faster, or slightly uphill you get closer to 45mm3. Under ideal conditions I can run ±30mm3 at 73-75 mph, and ±27mm3 at 65. That's main pulse, there is an additional amount of fuel for the pilot as well. In stock trim I would run closer to the 37-40mm3 range flat at 73, just goes to show you what timing (mainly) and pressure will do. With better timing and stock pressure I still ran closer to 33-35mm3 at 73 mph cruise.

I focused my rail pressure adjustments in the 30-45mm3 area, and then made the 0-30mm3 area a gradual increase to match the rest of the map. This is why the min pressure at those rpms is slightly higher than stock. Very little time is spent in those regions so the added pressure is not a hindrance, and with how little fuel is injected the added pressure does ensure a cleaner burn on a cold motor. I also raised my idle pressure for the same reason.

But when you look at the 30mm3 cells you can see I am lower pressure and lower timing than stock, with more fuel efficiency, a quieter motor, and a happier driver :-) The exception to that is the timing at 2200+ rpms. The stock timing DIVES at 2200+ rpms, and that is one of the reasons the stock trucks do so poorly at high speeds, especially a manual with the (.73,.74, or .79 OD) it's not as bad with the .69 on the 48RE. So now you can see why I was able to get ±21 at 73 the other day.

This next photos are my entire timing map vs the stock map. It's just for visuals, as rail pressure and duration are also adjusted timing must be modified so it's not a 1 size fits all timing map, it fits my pressure, duration, turbo, motor, and intended use.

Lastly, my pressure versus OEM. I also show OEM by itself so you can see how it's not smooth at all!

OEM

UDC

So now figure in real world items into all of this info and how it changes everything.Elevation, barometric pressure, humidity, ambient temps, different fuel types brands and quality of each. ect ect ect ect.:smart:Change just one and everything you are trying to figure out changes a lot.

So now figure in real world items into all of this info and how it changes everything. Elevation, barometric pressure, humidity, ambient temps, different fuel types brands and quality of each. ect ect ect ect. Change just one and everything you are trying to figure out changes a lot.

It will change how the power is made for sure, but if you are burning 34.5 mm3 (30mm3 main at 2200 rpms at 73mph) it doesn't matter what ambient conditions you are in, the mileage will be the same since you are burning "x" fuel at "y" speed. The ambient, timing, load, etc variables determine how much fuel you burn. So in reality you cannot make the mileage at 30mm3 any better, but you can make 30mm3 make more power and thus the ECM will go lower in the fueling table to make the require power, and that is how you save mileage. What's amazing is if you are burning 30mm3 at 1800 rpms or 2200 rpms the mileage is very similar, despite the increased speed and GPH.