Timing Effects

[ISX]

There is a part to this that just doesn't add up. At the top of this thread there is a chart showing that retarded timing decreases NOx output. It is obvious that a 24V runs it's timing much more advanced than a 12V by the way that they knock. Now looking here http://forum.mopar1973man.com/attachment.php?attachmentid=1543&d=1281643335 we see that Mike's 2002 has a NOx output of 3.8 and a particulate matter output of 0.10. My truck on the other hand http://www.mopar1973man.com//isx97/Truck%20Stuff/Ryan's%20Dodge/Engine%20Pull/IMG_0430.JPG has a NOx output of 4.8 and a particulate matter output of 0.09. This would indicate that my timing is much more advanced than a 24V, but that is surely not the case by how a 24V knocks. Now the 24V runs a higher pop pressure on the injectors. I don't know what it is but a 12V is 260 bar and I think a 24V is 310. Fuel that is atomized more will ignite faster because the atomized particle requires less heat to become hot enough to ignite. This means a 24V has advanced timing due to injector pressures. However, it isn't the timing that I think does it, I think it is the better atomization that reduces NOx. NOx is a huge emissions thing and new trucks are running upwards of 20,000psi so there has to be something relating to NOx and atomization. Now I don't know why the 24V's are so advanced if advancing increases NOx. There is hardly enough difference in engine design to say that something else is causing the incredible knocking sound. The new cummins' don't make a sound. I know they have multiple injections but even the first CR's are quiet. Soo why are only the VP trucks so advanced on timing? Then the chips you put on them advances it even more. By the way they sound it is like they are running 20* advanced, or more. I think there is something else going on but I don't know what.

[AH64ID]

Those NOX output numbers are probably at rated rpm, not at idle. The injector/piston relationship could also factor into the sound at idle on the 24V.Once UDC is released for the VP trucks we can get a good look at it's timing. On the CR trucks they idle right around -4° on the main event.

[ISX]

I know it's at rated RPM. But they are noisy at any RPM. I used to drive a 2002 6spd at work and I would short shift it just so I wouldn't have to listen to it. If the CR is that retarded then that makes perfect sense as to why they are so quiet. Mine was really quiet when the timing was really retarded. What is this UDC thing?

[AH64ID]

I know it's at rated RPM. But they are noisy at any RPM. I used to drive a 2002 6spd at work and I would short shift it just so I wouldn't have to listen to it. If the CR is that retarded then that makes perfect sense as to why they are so quiet. Mine was really quiet when the timing was really retarded. What is this UDC thing?

Yeah 24V's are noisy, but I think they are just as noisy with a P-pump conversion. www.madselectronics.com Yeah with the retarded main and the pilot it makes for a very quiet motor, and super easy starting.

[ISX]

I never thought of that! Time to go to the big forums and ask them.

[bbraden]

I recall seeing a list of what advance/retard timing does and if I recall correctly, advancing timing creates more NOx, but less particulate matter. When you retard, it does the inverse. Being as the engineers that were coming up with the VP system were probably doing this in 1997 or so, maybe particulate matter was the devil back then. It seems as though NOx emissions are a relatively new concern. I don't remember hearing anything about NOx before about 2006 really. If the engineers were trying to minimize PM rather than NOx, that might explain the crazy timing.

[ISX]

Well this took a weird turn. http://www.cumminsforum.com/forum/98-5-02-24v-p-pump-conversion/475540-24v-knock-ppumped-24v.html Basically they said it's the VP making all the racket. That makes a lot more sense than the insanely advanced timing that it sounds like. Also explains why the 2 stroke makes it a lot quieter though I have yet to hear a 24V with it in it in person. Hmmmmmmmm how the tables have turned.

[Mopar1973Man]

Geez... How much timing do you really need... (24* BTDC) is a bit much don't you think?

[ISX]

I don't know what their deal is but at least I got my answer. But then again the 24v sounds like a truck that's running 24* haha. That's why I think the pump making noise is a very logical culprit.

[AH64ID]

Good information. I have only heard one 24V P-Pump, think he had about 14-15°, but I thought it sounded like a 24V, but I have only heard 1, and don't spend a ton of time around 12Vs or 24Vs.

[mr.mindless]

I could really tell my 12v from my friend's 24v when we would park next to each other idling, I don't think I've done that since the 24v went in my truck. Back then I really just thought it sounded like twice as many things going on and I blamed the valve train. Not sure if that's still the case or not... I'll make a mental note to check next time we're running together and pull up for fuel next to each other again.

[bbraden]

I still think it is timing rattle. If it were the mechanics of the VP making the noise, why would it get quieter when it's hot outside and it's up to operating temp? I think the guys with the P-pumped 24v's are not good comparisons because there are so many different variables (i.e. cetane rating, pop pressure, injector hole sizing and quantity, inj line diameter, DV size) that can all change "EFFECTIVE" timing. One guy can say he's got 24 degrees timing, but the flame front could be totally different than another guy with 24 degrees depending on the setup. 2 stroke - I also noticed a major difference in sound when I add 2 stroke oil to my diesel. I think it has very little to do with lubing the mechanics, but MUCH more to do with effectively retarding the timing. 2 stroke oil is more resistant to compression ignition than diesel. Adding two stroke oil moves more of the ignition pressure peak ATDC and lengthens the entire combustion event (and smooths the peak) which decreases the "knock" that we all hear from the 24v. Same reason why WVO and WMO all quiet the motor down. Adding a slower burning fuel to the mix creates an injection event similar to what they were trying to acheive with the common rail: small fire at first, medium fire in the middle, small fire at the end to decrease any PEAK pressures and quiet the motor significantly.

[bbraden]

ISX:When you had your timing seriously retarded, how did the motor sound? Did it quiet way down and sound real smooth at idle?

[ISX]

Ohhhh yeah. Started up before the sound hit my ear as well.

[bbraden]

That's what I thought. I bet that you could make a 12v sound much like a 24v at idle if you advanced timing to about 30 degrees. Also, I bet you could make a 24v start on a dime and idle extremely smooth if you retarded timing to about 3 degrees at idle. This further makes my point that the noise associated with the 24v is a matter of building too much in-cylinder pressure BTDC, from having timing way too advanced.

[ISX]

That's what I thought. I bet that you could make a 12v sound much like a 24v at idle if you advanced timing to about 30 degrees. Also, I bet you could make a 24v start on a dime and idle extremely smooth if you retarded timing to about 3 degrees at idle. This further makes my point that the noise associated with the 24v is a matter of building too much in-cylinder pressure BTDC, from having timing way too advanced.

But if it already way too advanced, why does the edge chip advance it even more?

[bbraden]

To be honest with you, I don't know why anybody would run a programmer/box that advances timing. I have the Super X VP44 that comes with "timing advance" from the factory and I kinda regret it. It's a good pump and it makes real good power, but I think the power comes from higher injection pressure rather than timing advance. When I had my Edge Comp (timing box) hooked up, it made a whole lot of black smoke, but never produced much power until I hit about 2300 rpm. That's because timing was just way too advanced. I want my power from 800 rpm to 2000 rpm, where I can take advantage of it towing and on the street. If you use a Cummins like it was meant to be run, it shouldn't need any timing advance. I'm talkin never go over 2100 rpm. It's not until you get into the 2,000+ rpm that timing advance helps make any power. That doesn't do me much good with a trailer in tow, or just stop light to stop light. We've all drank the koolaid that advancing timing somehow increases low end torque, when the truth is, it hurts low end torque. The only difference at low RPM that you feel is from added fuel, rather than added timing.

[AH64ID]

A lot really depends on what truck, it's use, and how it was setup. Most timing has been done for emissions, and even the static timed P7100 was partially for emissions. The VP and CR use dynamic timing, which is for emissions and drive-ability. The dynamic timing allows for better starting, improved economy, and a flat torque curve. But in general I don't think anything would hurt from a little timing, heck I gained up to 55hp/100ft/lbs from 1600-2400 from timing along, and the motor is more responsive, smoother, and more efficient. Timing is good!

[bbraden]

Well, I could see where the CR motors might could use a little timing advance, especially since they're so strapped with emissions tuning. They probably came from the factory with timing too retarded anyways. On the VP motors, we've already asserted that it's too much timing that's making the rattle, meaning that we probably have more than enough anyways. I agree, it's all about the entire vehicle setup. Little things like gear ratios could dictate where the sweetest spot for timing is. I think we can all agree that the VP motors have too much timing advance on idle... timing programmers will only make that worse (if they add any timing at idle).

[AH64ID]

I thought the guys with P-pumped 24V's and 24° of timing don't have the rattle, and thats a LOT of timing, I don't think that the VP trucks have more than that at idle. I can't find it right now, but Michael has a chart that shows the timing vs rpm vs temp. I agree that just adding a static addition isn't the best, but a dynamic addition is good, even on a VP truck, just not too much.