bbraden

Wow... what I gained most out of that quote from Quad is that they just go the max on timing and they haven't put a whole lot of thought into how that works everyday driving/mileage, but only for max power. It's hard to say from the information there, but when he says "There is a too low and a too high number. If the IAT drops too low the ECU retards the timing just like too hot due to fears of detonation and stabilitiy of combustion in diesel fuels"... I would venture to say that "too low" is probably in the -degrees.

I was thinking about this again this morning... my DD ('93 Toyota pickup) is parked for the next couple mornings so I actually had to drive the Dodge again today. It was about 38 degrees here this morning and when I cranked the ol' gal up, she was just as clattery as usual. I was thinking about the attributes of advancing timing for a cold startup. 1) Cold air decreases flame speed which would require a little extra timing from the get-go. Hence "some" of the extra noise on a cold startup? 2) If an engineer were interested in getting an engine up to operating temperature more quickly, he would also advance the timing. Advancing timing increases the amount of time that the piston and head see flame frontage, driving more heat into both of them. This is common knowledge. If emissions required that our engine come to operating temperature sooner to minimize PM, this might be another driving force for running too much timing during cold starts. Advancing timing increases the amount of heat built in the cylinder, which forces more heat into the surrounding metal, which means that we see lower temperatures out the exhaust. Most people see this in lower EGT's when they run advanced, but they do not realize that much of that temperature is being ran through the radiator instead. Think about when you drive your pickup for a while (up to operating temp) and then you bring it back down to an idle. EGT sits around 350, right? Crank your cold engine up in the morning and see where the EGT sits. I'm not sure how conclusive that is... could be a matter of heat sink on the probe and exhaust stream and possibly not conclusive at all. This brings me back to the IAT fooler. We postulated that the foolers were advancing timing when set to higher temps, correct? If you need more advanced timing at colder temperatures, would it not be working the opposite way, by advancing during cold temps and retarding at hot temps? I think another experiment I would try if I had an IAT fooler would be to get the motor up to operating temp and let it idle for a while. Check your EGT at different intake temperatures (using the fooler) and see which ones increase EGT and decrease EGT. Might be worth a try?

I'm not familiar with Singh grooves... But yeah, I'm talking similar things to the super squish pistons/heads.

CSM, I agree 100% with your post. I didn't know that diesel burned that much slower than gasoline, even when artificially pressurized (turbo or super boost). Many VW gas engines run 30-32 degrees total advance when cruising under part throttle conditions. If we can increase the burn speed - whether by compression, smaller droplets, or more swirl - we can pull out more of the timing and create a more efficient engine. I was thinking about the difference in piston/head design between the 12v and 24v. I know that both engines have a more or less flat top piston with a combustion bowl built in, but would the injector direction cause a big difference? I know that the 12v injector sits at an angle... much like the plugs do on a fast burn head. I know with gasoline engines, head designs like the "fast burn" and Vortec heads lend themselves to better fuel economy. The smaller the intial combustion area, the higher pressure this little area sees. In the fast burn heads, the spark plug is directed in such a fashion as to be right in the middle of the smaller initial combustion area, and the valves are situated in such a way as to enhance swirl. Ideally, the combustion chamber is a wedge shape with the exhaust valve sitting at the smallest part of the wedge, so that exhaust is funneled out of the chamber more efficiently during the exhaust stroke. All of these things make for a more efficient combustion design that allows you to pull more timing out, but doesn't create knock. - - - Updated - - - Or maybe... it's as simple as combustion pressure. A 12v has 17.5:1 CR as far as I know. At 5 psi boost > 19.7 PSIA * 17.5 = 344.5 PSIA 24v non-HO has 16.3:1 CR. At 5 psi boost > 19.7 PSIA *16.3 = 321.11 PSIA. I'm sure this would have an effect on flame speed, and thus efficiency. If the 12v has higher compression, it should theoretically require less total advance - but that may be made up by the smaller droplet size on a 24v.

As most of ya'll know, Crazy Carl "Turbolver" put a supercharger on his P-pumped 24v. I've followed it very closely with great curiousity but haven't seen any talk about the timing. I read where he bumped timing from 15 degrees to 24 degrees, but he never reported back with results. How would a supercharger affect timing, and how could you maximize efficiency using one?My thoughts are: since extra boost (especially down low) increases flame speed of diesel, you might actually be able to retard timing and maintain similar EGT's and increase torque. Am I way off?

How interesting... I wonder where the extra injection events fall on those maps?

Absolutely. Peak pressure BTDC is not good at all. The CR injection system should theoretically be able to inject just about anywhere to get peak pressure wherever needed. Low boost levels + high RPM (where you would normally be during a cruising situation) should have the highest amount of advance, which is probably the majority of injection BTDC.

Have you optimized for fuel mileage yet? What mpg are you seeing?

Well, I haven't revisited this in a while, but it's way past time to stop back by. I've been reading a lot about one of my other hobbies - VW aircooled engines. I built my own dune buggy a few years back and have helped work on numerous others. About a year ago, I converted mine to run on propane like many rock crawlers do, and ever since then I have been on a quest to make it run on the least amount of fuel possible. In doing so, I've read and read about how to make a VW engine more efficient and have stumbled on lots of good information about timing. Granted, this is on a gasoline engine, but the theories are similar. Truthfully, it seems that as a whole, the gasoline tuner crowd has a much better understanding of timing than we do. As it turns out, timing BTDC is BAD. Ya'll may all understand this already, but it's really sunk into my head now. I've said this before and stood by it, but now I have a little better comprehension. In theory, the perfect engine would never have any combustion happening BTDC. Any pressure built BTDC is wasted as negative work against the piston. However, with our physically limited fuels, we have to start injecting BTDC in order to have peak pressures ATDC when the piston can actually make use of the fuel. On the same note, when we want to start increasing fuel input, it must be injected somewhere, so we advance timing and lengthen the event so that we can squeeze more fuel into the combustion chamber during the same event. Given too much timing, we are once again performing negative work on the piston. The only way to make a diesel more efficient is to perform more work ATDC without carrying over any of the event into the exhaust stroke. Decrease the amount of time it takes to make a complete burn in the power stroke, and you begin to see better efficiency. We do so by increasing cylinder pressure (boost). The higher the pressure, the faster the flame front. We can atomize the diesel more, making smaller droplets and a faster flame front. We can introduce swirl into the chamber (whether by valve structure, or piston/head design) which brings the fire around more quickly. We can decrease the viscosity of diesel to make it separate and atomize quicker and into smaller droplets. Particulate matter slows the combustion process, so we can evacuate the cylinder more quickly during the exhaust stroke to ensure all PM is out of the cylinder (difficult for the those EGR guys). NOS increases burn speed by increasing oxygen content, creating faster flame front. All of these things have a beneficial effect on timing, by making the fuel burn more quickly. Quicker burn = less timing required = more POSITIVE work on the piston = better fuel economy. Of course, as RPM increases, more timing will be required because the flame speed won't change, but the piston speed increases. This will require extra timing BTDC to continue building highest pressure ATDC. As the Cummins injection systems have continued improving and seeing higher and higher injection pressures, it becomes obvious that the newer (and higher the pressure) systems will NOT require as much timing advance because the flame speed is fast enough that the event can be over with before the end of the power stroke. BUT... we worked backwards by lengthening the single event out into three actual events for "noise control" or "pollution control" as is the case in the CR. In-cylinder EGR camshafts also work backwards to our goal by not evacuating all PM during the exhaust stroke. My thoughts are, if you were to get rid of all the extra events, in-cylinder EGR, and run the highest pressure possible for fastest flame speed and retard timing as close as you could to exert the most work on the piston ATDC, you would have an extremely efficient CR engine. Maybe everyone here knew all this, but it seems as if there is a LOT of hocus pocus about timing and nobody really understands the negative effect it can actually have.

Funny how these old threads get dug up! I'm curious as well. I'm getting ready to adjust my valves (never been adjusted and I'm at 230k miles) Yikes! My two cents: First - when you were asking about the necessity for valve lash - On Volkswagen motors, the rockers are designed such that everytime the lifter comes down to contact the valve, it actually causes the valve to rotate ever so slightly so that the valve is contantly rotating during operation. This keeps it from wearing abnormally. Cummins valves may have a similar design. Second - when talking about intake valve vs boost, don't forget that all things equal, if you open the intake valve sooner in the intake stroke, your turbo boost (measured at intake) should be lower. Many people don't understand that boost pressure is truly a measure of restriction. If your turbo were allowed to flow from compressor directly to atmosphere, it would make 0 psi boost, regardless of how fast it spun or how big the compressor is. Confine that airflow and that's how boost pressure is made. If you were to set your intake where it opened sooner, it's going to allow more air into the cylinder, which means some of that air volume creating backpressure outside the cylinder is going to get consumed inside the cylinder. Cylinder pressure goes up, but boost pressure goes down.

Then I guess the next logical question is - how does the VP, or any of the pumps for that matter, vary injection pressure if pump displacement is fixed?

Well... I think that the VP44 can do something very similarly to the CR by varying max injection pressure... but I don't have any evidence to back that up.

Is the pressure actually always the same in the rail of a CR? I thought that it fluctuated quite a bit with fueling requirements? Where it should be low at idle and higher at RPM's.

Taken off the Cummins Forum (NOT MY WORK!) This is actually a tuning "how-to" for the Quadzilla Adrenaline: _________________________________________________________________________________________________________ Pump Stretch. This will make the biggest difference in overall power and smoke. This is the amount of time the injector is actually opened and spraying fuel into the cylinder. I have this set pretty low on the 1000 tune that I sent you. The COMP file is set to 1800. More than 1800 creates more torque and a lot more smoke but, actually makes less power on the upper end based on all the trucks I have had on the dyno. This is where the COMP file is set to. Feel free to run it to 2400 anytime you want lots of low end power and smoke but, realize you are giving power up on the top. This does not mean you will get this amount of fuel all the time. There is a map, in percentages based off of this number as the maximum. Beyond that the map is also scaled by the TPS. So even if the map commands 100% but, you are at 50% throttle you will be getting 50% of the max stretch. If the map calls for 25% and you are at 50% TPS you will be getting 12.5% of the max stretch. ________________________________________________________________________________________________________ ..... This makes me question just exactly what capabilities the VP has. If it can vary how "long" the injector is open... could it make it such that the injection event is lower pressure (and lower volume) across the span of the event, but make the event so long that you get the same amount of volume in the end? This could possibly create an ignition event that is started way too early (causing timing knock), yet continue long enough into the power stroke that it's wasting fuel. From what I understand, one hot and fast event also creates NOx. The cooler you can keep the event, the more fuel you can give it, creating the least amount of NOx. If the event was lengthened out so that it never got extremely hot at one particular point, you could possibly make the same amount of power with more fuel, but with less NOx. Couple that with timing that's too advanced, and you have less fuel efficient combustion (with less NOx) at lower RPM and load levels. I guess it works like this in my head - 12v - pop set at 260 bar, pressure in injector lines exceed 260 bar and opens the pintle at say... 14 degrees BTDC. Injector remains open and injection pressure continues upward until a max of 1000 bar at say... 6 deg BTDC. Pressure spike begins decreasing at 6 deg BTDC, decreasing below 260 bar by TDC, closing the pintle. 24v - pop set at 310 bar, pressure in injector lines exceed 310 bar and opens the pintle at say... 24 degrees BTDC (timing knock). Injector remains open and injection pressure continues much more slowly upward until max of 500 bar at say... TDC. Pressure spike begins decreasing at TDC, decreasing below 310 bar by say... 24 deg ATDC, closing the pintle and ending the event (but burning much more inefficiently). If the VP44 can control pressure at any given time in the injection event, it should be able to accomplish such a thing. Just because the VP is capable of more MAX injection pressure than the P7100, doesn't mean that it necessarily uses that pressure all the time.

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?

http://www.turbodieselregister.com/tdrarticles/tdrarticle61_fueleconomy_pg3.html Some interesting reading here... basically negating everything we've lined out in this thread.

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.

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).

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.

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

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.

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.

I had a new thought on this a little while ago, and ya'll tell me if I'm way off.In a perfect world, the ECM on the 24v would advance timing (at low temps) just to the point that it offsets the timing requirement from the actual cold temps. This would basically create an even playing field between cold temps and hot temps because the computer compensates timing for the temperatures.Enter emissions crap. So how would the engineers at Cummins keep this thing making less emissions when it gets cold? Well... I figure they would do it about the same as they have done on all the other new diesels coming out - throw more fuel at it. (Richen mixture makes less NOx particles??)In the simplest, perfectly operating diesel engine, throwing more fuel at it creates higher RPM, as long as we're talking about an unthrottled engine. If you want to throw more fuel at a diesel without creating higher RPM, the only way you could acheive that is if you make the engine work against itself somehow. By introducing way too much timing advance, you create cylinder pressure sooner in the compression stroke, putting extra compression on the pistons BTDC, and basically working against the engine, almost like creating negative horsepower (in a sense). That's the only way that you could introduce more fuel without creating higher RPM's. Don't you normally have to raise the idle on a 12v when you advance timing? To test this, I think we could use the load function on the scanguage. (1) Warm the motor up to operating temperature. (2) Take a load reading at idle with IAT reading 140 degrees. (3) Take a load reading at idle with IAT reading 20 degrees. (Of course the grid heaters could not run as that would create excess alternator load.) If that doesn't read any difference, it might require a dyno load applied at a certain RPM and then see if the load reading changes. What do ya'll think?

That sounds exactly like mine with the Super X at anywhere below about 35 degrees. Except I can't turn the timing off. I was thinking either timing retard via the IAT sensor, or higher pop injectors that would put the event a little later in the compression stroke.