Timing Effects

[bbraden]

24 degrees of timing on a P-pumped 24v probably isn't that much if you have injector pops set at 310bar. I would still like to hear a a p-pumped 24v running that kind of timing with 260bar injectors. I would venture to say you could make it sound exactly like the VP'd motor if you kept advancing that timing...As for the programmers that advance timing, I would be interested to see if they actually add timing progressively like you're eluding to. It would make sense, being as the 24v with Edge doesn't idle much differently than 24v without, but I'm not sure that most programmers are sophisticated enough to do that. It seemed to me like (on my '07 CR) the Quadzilla XZT or whatever it was, made the idle a little louder, which I attributed also to extra "static" timing advance.I too have seen the chart with timing vs boost vs RPM, but unfortunately the numbers are never legible no matter whose version I see of it. That's sad... because it might could put all our debate to rest.

[AH64ID]

The XZT and Edge are not programmers, they are modules. But the Edge could be dynamic, the XZT would be less dynamic as all it does is effect the MAP signal, whereas the Edge plugs into the injectors. Here is a screen shot of some Smarty timing on a CR, I think a 03-04, as you can see it's quite dynamic. Blue is stock, pink is modified. It's a 3D map, so hard to get a single shot that shows it all, but this is pretty good I think.

[bbraden]

http://www.turbodieselregister.com/tdrarticles/tdrarticle61_fueleconomy_pg3.html

Some interesting reading here... basically negating everything we've lined out in this thread.

[ISX]

Both of your guys' posts were great. Still makes me wonder where all the knocking comes from on a VP44. Another weird thing is on my 215 pump there are retarding notches when you are at WOT. Some have said that's for packing more fuel in but I am thinking it must be an emissions thing. It retards it 4* from what I have heard.

[AH64ID]

Another weird thing is on my 215 pump there are retarding notches when you are at WOT. Some have said that's for packing more fuel in but I am thinking it must be an emissions thing. It retards it 4* from what I have heard.

It could also because with the added pressure of WOT and rpms you get more timing advance thru quicker ignition from the improved atomization.

[ISX]

It could also because with the added pressure of WOT and rpms you get more timing advance thru quicker ignition from the improved atomization.

You're gonna have to expand on this so I can wrap my head around why you think this way. Not doubting I just want to see it in the same light as you.

[AH64ID]

You're gonna have to expand on this so I can wrap my head around why you think this way. Not doubting I just want to see it in the same light as you.

As you increase rpms the pressure out of the P7100 increases, as the pressure increases you "advance" timing by two ways. One is the pressure hit's the pop pressure sooner and thus injects sooner, and the higher pressure atomizes better and flows faster (so more, easier to combust, fuel is injected sooner than at low rpms) and the fuel ignites faster. Both of those have an advancing effect on the actual ignition timing, even if the P7100 stayed completely static.

[ISX]

As you increase rpms the pressure out of the P7100 increases, as the pressure increases you "advance" timing by two ways. One is the pressure hit's the pop pressure sooner and thus injects sooner, and the higher pressure atomizes better and flows faster (so more, easier to combust, fuel is injected sooner than at low rpms) and the fuel ignites faster. Both of those have an advancing effect on the actual ignition timing, even if the P7100 stayed completely static.

I had to really think about it to grasp that I don't know how much difference it makes but I am thinking it really wouldn't do much more than a degree or 2, if that. But then again, I am not sure. The higher flow from the plungers going faster would just raise the pressure at the bottlenecks since at a constant plunger position they are going to pump the same amount of fuel regardless of RPM. This means at higher RPM it would be shoving the fuel through the bottlenecks like the delivery valves at higher pressure but the injector is going to pop the same amount of times as at low RPM (same plunger position) per piston stroke. I would like to think it advances but I am just not sure. Seems the laws of hydraulics would keep everything relatively the same. I will think more about this though.

[AH64ID]

If you delve into the common rail world you will find some more conversations on the topic. Same theory applies, fuel injected at 18K psi will ignite sooner than fuel injected at 10K psi. The P7100 is capable of 18,855 psi. Remember we are talking about the initial ignition point, not total fuel pumped. On a mechanical pump the pressure probably has a very little effect on total fuel, but it will still have some effect as you will spend a greater time above pop pressure.

[ISX]

If you delve into the common rail world you will find some more conversations on the topic. Same theory applies, fuel injected at 18K psi will ignite sooner than fuel injected at 10K psi. The P7100 is capable of 18,855 psi. Remember we are talking about the initial ignition point, not total fuel pumped. On a mechanical pump the pressure probably has a very little effect on total fuel, but it will still have some effect as you will spend a greater time above pop pressure.

Now I'm captivated. My injector says 260 bar which is 3771 psi. Are you saying that the plunger can jam 18,855psi out the delivery valve if it needs to and hence the injector sees that much at times? I would think that means the injector would be popping insanely fast rather than what I see on a pop tester lol. What can the VP44 pump out then?

[AH64ID]

That's the max pressure a Bosch white paper had, not sure what it does under normal driving or WOT. The VP44 is capable of approx 17,400 psi. CP3 in 03-07 is programmed to 23,106.

[bbraden]

As you increase rpms the pressure out of the P7100 increases, as the pressure increases you "advance" timing by two ways. One is the pressure hit's the pop pressure sooner and thus injects sooner, and the higher pressure atomizes better and flows faster (so more, easier to combust, fuel is injected sooner than at low rpms) and the fuel ignites faster. Both of those have an advancing effect on the actual ignition timing, even if the P7100 stayed completely static.

Boost, more often than not, also increases as RPM increases, which would additionally advance effective timing. So to get back to our VP-44 conundrum... what is it that makes the VP burn more fuel when it's cold. Obviously it's something computer controlled, so what all parameters can the VP-44 control/manipulate to make power? 1 - Timing Advance/Retard 2 - Event duration 3 - Injection Pressure? How does the VP vary the amount of fuel injected if not by duration? Pressure?

[Mopar1973Man]

Basically pressure and timing that it comes down too... Because duration is a factor of injector size so larger injectors have a shorter duration with the same pressure. Of course reverse than and have a stock or smaller injector and it takes a longer duration to inject the same amount of pressure. Because the injectors open up after 4,500 PSI roughly and start injecting fuel till the pressure falls below 4,500 again. To be real about it the pressure actually goes up and down on the injectors (called chattering)...What am I saying here... :banghead:

[mr.mindless]

Of course reverse than and have a stock or smaller injector and it takes a longer duration to inject the same quantity of fuel.

With the pump stroke, you're dealing with injecting a fixed volume of fuel (in a given circumstance) and varying pressure and rate with pump type and injector size, so it will take a longer or shorter duration to get that fixed quantity through the nozzle based on the volume the injector can pass.

[ISX]

That makes me wonder if there is a point where you can put too much fuel to it. If I do enough rack mods to get full rack travel and I get the fuel pressure to run at 50psi, is it possible that when I am WOT that it would try to shove so much fuel out of the stock injector, that the pressure rise would get to the point that the injector cracks or the injector lines burst? Seems possible. I have another thing to start a thread on that has to do with duration that will be very intersting to discuss.

[mr.mindless]

duration is a very important component of timing that seems to be ignored in most corners of the Cummins world. well studied in TDI circles - where smaller things make changes more apparent I'd expect. Same requested injected quantity through a bigger hole gives less smoke and lower EGTs because more of the fuel is shoved through the hole sooner giving a shorter ignition event and more accurate timing.

[Mopar1973Man]

That makes me wonder if there is a point where you can put too much fuel to it. If I do enough rack mods to get full rack travel and I get the fuel pressure to run at 50psi, is it possible that when I am WOT that it would try to shove so much fuel out of the stock injector, that the pressure rise would get to the point that the injector cracks or the injector lines burst? Seems possible. I have another thing to start a thread on that has to do with duration that will be very intersting to discuss.

Supposedly on the 1st Gen's it possible to rupture a injector line with a VE pump turned up too far. I've never seen it but heard of such happening. If its true or not I'm not sure.

[ISX]

Ah so it is possible. Probably hard to ever get to that breaking point. I think there is a fine line between optimum duration and optimum atomization. If you get a big injector, the duration will be short but the atomization won't be as good. Get a small injector and the atomization is good but the duration is long. Everyone seems to gain mileage with those RV275's so I am betting the duration was too long on the smaller injectors.

[Mopar1973Man]

Ah so it is possible. Probably hard to ever get to that breaking point. I think there is a fine line between optimum duration and optimum atomization. If you get a big injector, the duration will be short but the atomization won't be as good. Get a small injector and the atomization is good but the duration is long. Everyone seems to gain mileage with those RV275's so I am betting the duration was too long on the smaller injectors.

Once you get to about +75 HP (and above) injector then the MPG are neutral again from stock so now the duration is too short and atomization is poor. I'm not saying this is the case with everyone just saying general rule here...

[AH64ID]

Once you get to about +75 HP (and above) injector then the MPG are neutral again from stock so now the duration is too short and atomization is poor. I'm not saying this is the case with everyone just saying general rule here...

It's about the same on a HPCR. 50's provide an increase, 90's no change, and 90+ a decrease... again as a generalization.