Newby Starting off (again) '04.5 Economy tune help needed (with a lot of extra info)

[JDSDiesel]

Hey all,
I've been lurking for quite a while, and been trying to just read and learn. Jim and Steve, you guys have been a plethora of help.
I purchased and studied the course from HP acadamy, which seemed redundant to what I was reading here (so consensus is nice) But I will admit that I feel like I just am not getting it, and this tuning thing has been a lot of frustration for the last 9-months.
Usually, the story is I'm just starting to get some tweaks going, Then I end up changing something huge like Bigger injectors or tires, and I'm back to the drawing-board.
Those physical mods dropped my fuel mileage from 17.xx to 13.xx (not surprised) and now I'm wanting to get this engine to run more efficiently to see if I can get much of that back.
Yes, I know that you "Don't buy these trucks for the mileage" and "if you want economy, don't put mods on" but I feel like it had room for improvement before those 2 swaps, and I just wasn't uncovering the secrets this thing needed.
So, I'm hoping to get help on some basic questions, and consolidate knowledge that seems to be impossible to find sifting through the pages of the Cummins diesel forum.

One such question:
When/where/how much duration should I be cutting to compensate for these bigger injectors??
Details:
They're BBi Stage-1s, (roughly 30% overs or +90s) and The smoke is really NOT that bad on the stock tune, and I've even removed the post events before trying to use them to spool the turbo faster.
Speed limit is 70-80mph, and I now cruise 60-70. Which is turning 1500-1800RPMs. Boost was at 4-5psi @65 on flat ground, but after I advanced the Main timing 3* and boost actually climbed to 8-12 at the same speed (weird, I thought)

I THINK that my throttle position was 20-30% (guessing, as I cannot find my log files ATM)
5000ft elevation, and below freezing about 1/2 of the year.

SO, I know that cutting duration will also advance timing: (so to ask again, and ask about a very specific part of the tune) where/how much can I cut duration? Can I do it across the board? across the throttle range? Would it taper off as demand/pressure tapers off??

How to I get this pig to squeal??

Many thanks in advance,

[Jim P]

SO, I know that cutting duration will also advance timing

Absolutely nothing advances timing other than the timing tables, altering the duration table will not advance or retard timing, altering rail pressure table will not advance or retard timing, only the timing tables accomplish advancing timing.

Cutting duration only cuts duration, or reducing the amount of time the injectors will be open for at x amount fuel quantity commanded at x amount of rail pressure. The beginning of injection remains whatever you put in your timing table.

[Jim P]

The BBI injectors come with flow charts, they will give an idea of how much duration in needed to flow x amount of fuel at x amount of pressure. If you compare it to the stock duration table you will notice that at low pressure and fuel quantity they are almost no different from stock but there is a point where they starting flowing exponentially more fuel with less duration compared to stock.

[JDSDiesel]

Ok, let me restate that, just to make sure that I’m totally off base, or if I just said it wrong:
As I understand the concept,
IF one has a larger injector, and uses a shorter duration to inject the same amount of fuel, AND has the same injection start time (relative to crank angle) then this has the effect of advancing the injection event, Since the end of injection would be advanced relative to crank angle,. Nnow (again, as I understand it) this extra fuel can cause a slightly longer ignition delay too, so...
Again, I could be totally off here! Gawd knows it wouldn’t be the only time while I try to wrap my head around this...

And yes, I have the flow chart, I will go back and study that some more.
Thanks for all your help Jim.

[Jim P]

So here?s what?s actually happening when you install larger injectors. 99% of people, while knowing they are injecting more fuel from larger injectors seem to twist this into meaning they?ve effectively advanced timing which is incorrect.

Assuming you are leaving everything else tuning wise the same (or stock) and you install larger injectors, you are injecting more fuel over at the same starting points for the same period of time. Your pilot injection still starts at the same time and for the same period of time but has injected more fuel due to the higher flow rate of the injectors. The main injection event still starts at the same time and for the same period of time but has injected more fuel due to the higher flow rate of the injectors and same for the post injection event.

Nothing with timing itself has changed whatsoever, fuel rate has increased in all 3 injection events though and this leads to a higher rate of rise in cylinder pressure leading to an earlier ignition of fuel in the cylinder which can lead to what many refer to as injector knock. This injector knock as many like to call it is the equivalent to pre-detonation in a gasoline engine. It?s a rapid rate of rise in cylinder pressures that causes the knock in a diesel engine. One of the purposes of the pilot injection event is to control and reduce the rate of rise of the cylinder pressures.

If you know reduce injection pulsewidth so to match stock fueling, well nothing with timing has changed but you are now flowing stock fueling in a shorter period of time. This still affects the rate of rise in cylinder pressures and can still have a rapid rate of rise in pressures. With rapid rate of rise your fuel combustion process is faster and more volatile.

One of the points of timing is to control where in the engine cycle the peak pressure occurs, optimal point is approximately 2 degrees after top dead center. Being more aggressive with injecting same fuel in a shorter period of time directly affects the rate of rise of cylinder pressures which directly affects where the peak cylinder pressures occur in the engine cycle, thus leading to the need to adjust timing to bring the peak cylinder pressures back to where they should be occurring during in the engine cycle.

It?s all about the peak pressures and rate of rise of cylinder pressures.

[Jim P]

The 2003-2004 BBI stage 1 injectors are rated by BBI at a 30% increase at 100bar. So in your pulsewidth table, everything in the 100bar/100mPa column can be reduced by 30% to match stock flow at that pressure, all other pressures you?d have to kinda extrapolate from their provided flow chart to get its flow characteristics somewhat like stock if that?s your goal. You?ll notice in the chart that at lower pressures and volumes the time is pretty much stock values then after a point they start deviating away from stock numbers.

[JDSDiesel]

Yes sir, I did notice that from when I First saw the flow chart.
ie, Everything starts at 0, and the the difference grows Further apart as the number (x-axis) approaches higher numbers.
It?s actually a pretty linear growth over stock. So can I safely assume that I could blend and smooth the table between 0 and 100bar??. (30% at 100bar, 27% at 90bar, 24% at 80, etc etc). Then I?d guess I account for the one ?big? change in slope at the lower pressures of the X-axis. (Taking 1-2% off each step, rather than 3%?)

Also, thanks for the re-explanation. It Makes perfect sense now.

[Everytime5.9]

Do you have a tune to post? Did you have a good tune before the injectors?

Keep your PW table stock and just adjust the 80 or 100mm3+ for now.

With my BBI stage 1's I had 1700us with 18* @3000rpm for a low tune.

Then bumped it up to 1785us at 18.9*. My timing map is similar to what i had for stock injectors at 2100us for these lower tunes.