Max cruise timing

arinkuddy said:

I wondered how the old 12 valves got such good mileage with the lower pressure and im assuming wider pulse. Less parasitic losses from injection system? No pilot?

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Simple they are better in every way.

From my understanding the new cam and everything about the engine don't really promote fuel milage as much as emissions

Ghostman said:

My pressure runs around 18k in the cruising range. I don't seem to have an issue with that pressure.

@Arinkuddy - so the table with less main timing got worse mpg. I think I would expect that. What kind of mileage are you getting?



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I'm getting about 18mpg with 60-80mph and a little city traffic... forgot to put that

malibu795 said:

On the dmax there are about 8-10 main tables that have to "jive" to get smooth respone on a general tune.

Moving rail pressure in sooner throws throttle, timing, Mm3, boost all off the normal operating area of the charts and they all have to be adjusted to get smooth operations again

Empty I run less then 20% throttle, realy touchy for most, Loaded I'm 25-40% throttle
Stock setup ID be 35-45 Empty loaded be 60-75% for same fueling...

I've got my dmax setup I can go full fuel by 1800rpm with timing adjusted for throttle and RPM, as full timing at 1800 that I run at 3000 would hurt the engine..

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I've looked at duramax stock files before and I wouldnt know where to begin with them. Quite a bit more to take into account vs an 06 cummins.

Isn't % throttle a relatively useless metric to use? The amount of fuel is a function of pressure and duration which would equate to some quantity of fuel. Increasing pressure or PW would make less throttle put more fuel, seems that way on cummins anyway.

97rada said:

Simple they are better in every way.

From my understanding the new cam and everything about the engine don't really promote fuel milage as much as emissions

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ha im beginning to think so.... hell if it wasn't for the EPA you could probably buy a 2015 truck with a 12 valve in it.

I've heard that before that the cam isn't very efficient for economy, something about the lobe separation angle. Just not worth the $800 or whatever for another 1-2 mpg

I myself am very interested in swapping a cam to see if it makes a difference in economy. Out of all the year model trucks, I think these could see the most benefit from it.


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arinkuddy said:

I've looked at duramax stock files before and I wouldnt know where to begin with them. Quite a bit more to take into account vs an 06 cummins.

Isn't % throttle a relatively useless metric to use? The amount of fuel is a function of pressure and duration which would equate to some quantity of fuel. Increasing pressure or PW would make less throttle put more fuel, seems that way on cummins anyway.

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The LMM starts
tps%/rpm=TQ
Tq/rpm=mm3
Mm3/rpm= rail pressure
mm3/rail pressure=pulse width
Mm3/RPM=timing (pilot timing is similar though has additional factors contributing to it such as ECT, TPS, RPM, and time between pilot/main injection(s))
Outside boost/MAF/map table these are probably 75-80% of the tune
Educated gues Cummins did something similar.. Haven't looked a Cummins tune in for ever.. Lol

I have yet to see two factory tune trucks of same year and engine with the exactly same tune when you plot it out..

Throttle % and TQ/rpm table are the proverbial linkage between your foot and the carburetor. And pretty much what all the other tables go off of for basic info.

Yes fuel is a function/result and RP and PW. Increase RP with same PW equals more fuel.
If you go from say 2500rpm is 20000psi RP at 50mm3 to 2000rpm and 30mm3 with nothing else changed good chance to have some surging.. That's alot of fuel alot sooner

Here is OEM stock LMM rail pressure table

And what I'm currently running

I can tell you the latter rail map sucks on a relatively stock tune..
Only downside I've found to higher rail pressure is fuel return, gets hotter faster especially in summer, wouldn't surprise me if Cummins has a high return fuel temp limit in which is derates the engine.

arinkuddy said:

I agree, I wouldn't dare run that high of pressure cruising. I actually use slightly lower than stock cruise pressure where it spikes a little around 45mm3. I actually was theorizing that the extra hp used by the cp3 to get that pressure may cause diminishing returns anyway.

I wondered how the old 12 valves got such good mileage with the lower pressure and im assuming wider pulse. Less parasitic losses from injection system? No pilot?

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They were a little bit lighter trucks I think. I wonder if the pulse was shorter. I think they lengthened out the pulse for NOx reduction. That's part of the reason the timing is late on these 04.5 to 07's. I also wonder if these newer cooling systems are a bit parasitic. The 96 my boss had would warm up a bit if you stayed in it too long making roughly the same HP mine is making.

Ghostman said:

I myself am very interested in swapping a cam to see if it makes a difference in economy. Out of all the year model trucks, I think these could see the most benefit from it.


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A friend of mine had an 03 that might have gotten roughly 3 mpg more then mine does. It's either the pistons/ injectors or camshaft. I wondered about a 178/208 but it is really a pain. Now I wonder what would work best with something REAL Skookum hanging off the passenger side of that engine. Almost feel like if I'm going to that much trouble, instead of gradual increases, just start off big. :nail:

arinkuddy said:

No your fine and true, idk I'll have to really look closely at it.

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Will your truck pulsate with cruise control set?

phale said:

no pilot tunes produce pretty good mileage because you have to run a minimum positive timing value. On a multi injection tune timing is often negative except for the actual cruising area. Get off of the cruising part of the table and you can go from 8* to -5* pretty quick depending on how you build the table which hurts economy but is useful for other things. The minimum 5-8* needed for a single event tune to run properly ensures you are always running timing conducive to economy while it may not deliver the best results in other areas.

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Are you suggesting that on a 6.7 specifically, when cruising ONLY, that you take the pilot event out and run ~8* timing? This is very interesting...