Timing Effects

[hd99fxr3]

I wonder if Singh grooves in the piston dome, would promote a faster burn rate, like it does in my HD? Put the grooves in those heads, and even though I have 10-1 compression I can run regular unleaded in a pinch without detonation.

[bbraden]

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

[hd99fxr3]

http://somender-singh.com/content/view/7/31/

[AH64ID]

Don't forget that boost is measure of resistance, and not flow. So 5 psi on a 12V head is not the same as 5 psi on a 24V head, just like 5 psi on my truck is a lot more air than 5psi on 05 with a stock cam/turbo.

[CSM]

I wonder if Singh grooves in the piston dome, would promote a faster burn rate, like it does in my HD? Put the grooves in those heads, and even though I have 10-1 compression I can run regular unleaded in a pinch without detonation.

Interesting. Those grooves are giving you a bit lower compression, and are giving more turbulence and "mixing" in the chamber. I've talked to guys that said they would do that back in the 40s to get by on lower grade gas without pinging. You can get that effect to the point that it blows the flame out at the spark plug though. I personally don't feel that "being aimed at the spark plug" means jack. There just isn't anywhere else to groove on most chambers, as the valves take up most of the area. Some of the car manufacturers really started playing with their chamber designs in a big way about 20 years ago, and it has started to become a bit more popular in hot rod realm. The best overall way to get turbulence in the fuel/air mixture is to design a quench pad to the chamber. The piston will basically get really darn close to the head, close enough to put out the flame on that side and push any of it over to the other side. In the process though, it really rapidly pushes the fuel/air mixture across the chamber and helps eliminate any rich/lean spots in that particular charge of fuel/air. With this more ideally mixed fuel/air charge, preignition or detonation is far less likely. But there are lots of different terms and effects in the chamber that I don't recall the proper definitions for, quench, squish, swirl, etc. Steve Dulich, in Engine Masters magazine has had some great articles over the past decade for gasoline engines. In diesels, this effect is already done, and in a beautiful way on our Cummins engines. Part of the chamber is actually in the piston, the charge actually compresses into that void in the top of the piston. The charge of air is quite turbulent in that little space, then fuel is squirted in via the injector. The fuel/air mixture doesn't burn the same as gasoline, but with a properly designed combustion chamber, and good injector spray (ie: small droplets) you can have great clean power. Any significant change in the chamber design would likely have to be met with a change in fuel timing to be optimized... Though, in theory, additional compression would give an increase in efficiency... A higher compression engine (like the H.O.) with a smaller more efficient turbo running at lower speed could give some near ideal efficiency. Chamber design can make some really great engines, but they are also somewhat touchy. In my opinion, like porting, its somewhat a trial and error art form until someone gets it right. There is a lot going on that is extremely hard to model... but building stuff can be the fun part so long as the pocketbook holds out.

[dorkweed]

Don't forget that boost is measure of resistance, and not flow. So 5 psi on a 12V head is not the same as 5 psi on a 24V head,just like 5 psi on my truck is a lot more air than 5psi on 05 with a stock cam/turbo.

Show off!!!!

[CSM]

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.

I think it would, but its going to be hard to have an apples and apples comparison. What we would need is a 12v vs 12v or 24 vs 24... with different compressions so to speak. Efficiency is directly proportional to compression ratio. More compression = more efficiency, regardless of boost. However, flame speed is a function of pressure. As the Apache says, boost is a measure of restriction, and it may be very hard to actually measure the effective boost gained within the cylinder... and its going to be a function of load & RPM. I think this is where tuning comes in, and I am uber jealous of those 12V and CR guys with their "adjustability" with your wrenches and smarty, respectively.

[hd99fxr3]

Interesting. Those grooves are giving you a bit lower compression, and are giving more turbulence and "mixing" in the chamber. I've talked to guys that said they would do that back in the 40s to get by on lower grade gas without pinging. You can get that effect to the point that it blows the flame out at the spark plug though. I personally don't feel that "being aimed at the spark plug" means jack. There just isn't anywhere else to groove on most chambers, as the valves take up most of the area. Some of the car manufacturers really started playing with their chamber designs in a big way about 20 years ago, and it has started to become a bit more popular in hot rod realm. The best overall way to get turbulence in the fuel/air mixture is to design a quench pad to the chamber. The piston will basically get really darn close to the head, close enough to put out the flame on that side and push any of it over to the other side. In the process though, it really rapidly pushes the fuel/air mixture across the chamber and helps eliminate any rich/lean spots in that particular charge of fuel/air. With this more ideally mixed fuel/air charge, preignition or detonation is far less likely. But there are lots of different terms and effects in the chamber that I don't recall the proper definitions for, quench, squish, swirl, etc. Steve Dulich, in Engine Masters magazine has had some great articles over the past decade for gasoline engines. In diesels, this effect is already done, and in a beautiful way on our Cummins engines. Part of the chamber is actually in the piston, the charge actually compresses into that void in the top of the piston. The charge of air is quite turbulent in that little space, then fuel is squirted in via the injector. The fuel/air mixture doesn't burn the same as gasoline, but with a properly designed combustion chamber, and good injector spray (ie: small droplets) you can have great clean power. Any significant change in the chamber design would likely have to be met with a change in fuel timing to be optimized... Though, in theory, additional compression would give an increase in efficiency... A higher compression engine (like the H.O.) with a smaller more efficient turbo running at lower speed could give some near ideal efficiency. Chamber design can make some really great engines, but they are also somewhat touchy. In my opinion, like porting, its somewhat a trial and error art form until someone gets it right. There is a lot going on that is extremely hard to model... but building stuff can be the fun part so long as the pocketbook holds out.

I failed to mention, I'm running a .029 squish in that engine as well. I was able to pull fuel and timing from high load areas in the map, because of the grooves. They don't do anything for power as far as I'm concerned, but I am convinced that they allow a better tune, and driveability. The compression loss is minimal not even a tenth of a point with an 84cc chamber.

[bbraden]

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?

[Mopar1973Man]

Right from Quadzilla's lab techs...

[h=2]Update - Tidbit from Quadzilla[/h] No doubt, stabilizing the IAT will help, I agree 110%. 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. No doubt winter blend fuel hurts this as well.

So you can definitely stabilize things but, I think the anomoly in the summer time is that when running a box with timing advance you actually get a steeper timing advance curve from the box by fooling the IAT.

The way the timing and fueling works on the can bus on these trucks is that we all just basically go to the MAX allowable advance and fuel number as soon as the VP computer will let us without locking it up. We can physically demand more fuel and timng but, the VP computer will shut down thinking there is an issue. As a matter of fact our peak numbers for fuel and timing can already be reached on a stock truck, its just that we can re-shape that curve and reach those max #'s when and where we want.

So basically fooling the IAT retards the timing and the box sees the opportunity to make an even bigger change going to max and it does it sooner.

Sort of complicated but, I can see where it works.

What we need to do on these older trucks is some tracking of the IAT across the actual timing advance range at the pump and not via the OBD port since its slow and suspect on that sort of parameter, I know when we start changing the fueling the timing numbers the obd reports some weird stuff that is not exactly right.

[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.

[AH64ID]

Since most of the temperature to the coolant comes from gas temperature in the head advancing the timing can actually slow warm up (think low/mid throttle, not heavy throttle like towing). The piston does see more heat, but it's absorbed by the oil and not the coolant. A retarded timing helps warm up the coolant quicker. I do agree about IAT and timing. I know that the IAT foolers increase the temp and mileage increases, but everything I know about diesel timing says that as IAT increases timing should retard. I have spent many many hours reading about timing in the last year, as I am now writing my own timing map. "--IAT or intake air temperature is important because the temperature of the compressedcylinder greatly affects ignition delay, and speed of the ignition event. Warmer airspeeds up fuel evaporation, reduces ignition delay and combustion duration, thusinjection timing must be retarded. If the PCM does not account for this, then the motorwill find itself losing power with non-optimum, advanced ignition. This is especially trueif IAT increases with the increase in vehicle effort, in a thermal feedback relationship.Increase IAT retard timing."I do think it's possible that the timing is retarding and mileage is increasing, and here is why. On my truck I was running about 8° of timing at cruise rpms and wasn't getting the mileage I expected. I dropped the timing to about 3-4° and load went down, and economy went up. So it's all about perfecting the injection, and ignition delay to get peak pressure at about 12-15° ATDC for optimal performance/economy. This is one reason electronically controlled timing is far better than dynamic timing. If you set a static pump at 16° timing it's always 16°, whether it's injecting 10mm3 at 1400rpms or 130mm3 at 2800 rpms. In one instance your injecting it way too soon, and in another way too late, and thus you get a narrow rpm band of optimal performance. But if you setup your timing to take rpms and pulse width into account you can control peak pressure better. It's possible that the timing map on the VP is a little too advanced at normal cruise temps for optimal efficiency, and retarding the timing a little makes for more cylinder pressure at the proper time. That is all just speculation, as I have no clue what is actually happening to timing with the IAT fooler, but by all reason it should be retarding.

[Mopar1973Man]

It the blind beauty of the VP44 pumps. So little information about then and more of a science experiment trying to gain as much MPG's as possible.

[ISX]

Since most of the temperature to the coolant comes from gas temperature in the head advancing the timing can actually slow warm up (think low/mid throttle, not heavy throttle like towing). The piston does see more heat, but it's absorbed by the oil and not the coolant. A retarded timing helps warm up the coolant quicker. I do agree about IAT and timing. I know that the IAT foolers increase the temp and mileage increases, but everything I know about diesel timing says that as IAT increases timing should retard. I have spent many many hours reading about timing in the last year, as I am now writing my own timing map. "--IAT or intake air temperature is important because the temperature of the compressed cylinder greatly affects ignition delay, and speed of the ignition event. Warmer air speeds up fuel evaporation, reduces ignition delay and combustion duration, thus injection timing must be retarded. If the PCM does not account for this, then the motor will find itself losing power with non-optimum, advanced ignition. This is especially true if IAT increases with the increase in vehicle effort, in a thermal feedback relationship. Increase IAT retard timing." I do think it's possible that the timing is retarding and mileage is increasing, and here is why. On my truck I was running about 8° of timing at cruise rpms and wasn't getting the mileage I expected. I dropped the timing to about 3-4° and load went down, and economy went up. So it's all about perfecting the injection, and ignition delay to get peak pressure at about 12-15° ATDC for optimal performance/economy. This is one reason electronically controlled timing is far better than dynamic timing. If you set a dynamic pump at 16° timing it's always 16°, whether it's injecting 10mm3 at 1400rpms or 130mm3 at 2800 rpms. In one instance your injecting it way too soon, and in another way too late, and thus you get a narrow rpm band of optimal performance. But if you setup your timing to take rpms and pulse width into account you can control peak pressure better. It's possible that the timing map on the VP is a little too advanced at normal cruise temps for optimal efficiency, and retarding the timing a little makes for more cylinder pressure at the proper time. That is all just speculation, as I have no clue what is actually happening to timing with the IAT fooler, but by all reason it should be retarding.

I think you are right. The whole IAT fooler idea came about when me and Mike were talking about the differences between our trucks. I have static timing (I think thats what you meant when you said dynamic) and so it's always at the same timing. This has drawbacks on paper, but in real life I am getting incredible mileage as are other 12 valve guys. Now this is kinda shrugged off for some reason but I noticed in the winter, my mileage was still high. The temps went all the way to -10F here and I never added any sort of antigel so it's not like this wasn't winter fuel as everyone blames their crappy mileage on. So me and Mike started thinking...cause his mileage goes down in the winter as does everyone else's apparently with a 24V (never really read anything about other 12V guys) so I thought about the differences. And if you think about it, in the winter there really is only ONE thing different between summer and winter driving. The boost is roughly the same, ECT gets to the same 190F.....but the IAT, that damn IAT.....changes. So I said fool that thing like you do with the cold idle thing, except backwards, make it think its summer and see what happens, because I see no mileage drop... and low and behold, no more mileage drop. Now this also stemmed from him telling me that when he starts it in the morning when it's freezing, that it sounds like a bunch of ball peen hammers. But to me, even when warmed up those things sound like ball peen hammers lol. So I had the thought that all this talk about advancing them had accumulated and now you had a truck thats 20* advanced, though compared to a 12V at 20* it sounds even more advanced. So if you fool it in the winter to make it think it's hot, then the overly advanced stuff stops and it goes back into normal timing mode that its in during the summer. It might be more for emissions even, but if we can fool it then why not. It's not like there aren't 12valves running retarded timing for millions of miles.

[AH64ID]

I think a lot of the 12V mileage is more than static timing. (fixed my post, thanks). There are many things to consider, but generally the 12V trucks have less emissions, so things like the cam and turbo can be more efficient. The vehicles are older, and thus of lighter construction. They also build power slower, so when an small grade hits the 12V will fuel into it more slowly/linear with throttle changes, where a VP or especially a CR can over-fuel and then find what it needs, the joy of ECM controlled injectors I bet if you were to put a HPCR, with a non-emissions turbo/cam/tune, into your truck your mileage would go up over where it is now. Why, because you can tune the motor to have the timing make peak pressure at the optimal crank angle at any rpm/load, thus getting more power out of the powerstroke.

[ISX]

I think a lot of the 12V mileage is more than static timing. (fixed my post, thanks). There are many things to consider, but generally the 12V trucks have less emissions, so things like the cam and turbo can be more efficient. The vehicles are older, and thus of lighter construction. They also build power slower, so when an small grade hits the 12V will fuel into it more slowly/linear with throttle changes, where a VP or especially a CR can over-fuel and then find what it needs, the joy of ECM controlled injectors I bet if you were to put a HPCR, with a non-emissions turbo/cam/tune, into your truck your mileage would go up over where it is now. Why, because you can tune the motor to have the timing make peak pressure at the optimal crank angle at any rpm/load, thus getting more power out of the powerstroke.

I'm gonna have to debate the older/lighter thing. They are the same trucks from 94-02... I know they upgraded a little and you can say the engine is heavier, interior might be heavier, but come on, we are talking maybe 500lb difference if I exaggerate it like crazy.. I put 500lbs worth of engine blocks in the bed of my truck all winter and don't see a difference in mileage. These things aren't like gassers that get half the mileage per 1000lbs extra. They hardly notice weight at all. Dorkweed I think said he got 18 pulling his trailer and gets I think 22 unloaded so that just proves my point even more. 12 more valves do not add enough weight to drop a couple MPG's... Another thing I notice is how much you have to baby a 24V to get over 20mpg, I beat the hell out of mine and can't get UNDER 20 unloaded. The timing is all good but, it's like it's set up for the wrong parameters all the time. I am sure it has to do with emissions as usual, but it's emissions and JUST emissions, nothing else is a factor IMO. Now there is the issue that people come up with from winter fuel burning faster. I can see that, but, colder air in and hotter air out is the formula for efficiency. I believe the cold air makes up for the theoretical fuel energy and therefore keeps mileage consistent throughout the year. Winter fuel in the summer I would think would drop a mpg. Summer fuel in the winter would gain you a mpg over your usual summer mileage. I only think this because I didn't put winter fronts on one year and it got to -10F and I had to get on the interstate and the thing made 5psi more boost and was an absolute bat out of hell. I haven't touched winter fronts since and see no difference other than more power. The thermostat controls the engine temp, not winter fronts.. Now another thing is that the 24V actually produces more particulate matter than the 12V according to the engine label. The focus was Nox so the 24V is lower there but I think they did it with timing, making it really advanced and that is why they aren't as efficient, they are overly advanced. We already went over this though but the whole deal revolves around emissions. Thing is, ppumped 24valves get the same mileage as the vp, if not worse, so I have almost wondered if the block itself has issues with efficiency, though I think it's identical to a 12valve block besides the head, so is it the head thats inefficient? Who knows. I'm just saying there seems to be a lot of interesting variables, emissions being the major one but sometimes I wonder if reprogramming the VP so that it's at max efficiency rather than for emissions, would actually get it up to 12v efficiency, because obviously a ppump on a 24v doesn't fix it, so what else could be the issue..

[AH64ID]

Don't forget the more fuel you inject, the closer you get to making peak pressure at the optimal crank position. With too much timing and you end up igniting too early and create a bit of negative torque. So you are probably more efficient at 40% throttle than 10% throttle. Does that mean more mileage beating on it than not, well it might, or might not. Timing my be setup less optimally in a VP truck, but the timing is setup wrong on the p-pump trucks 99% of the time. Even the stock 14.5° of timing is only 100% ideal at near WOT at 2000 rpms ± 200 rpms. So that's not really much of an argument either. In order to reduce NOx you need to retard timing, NOx is created by high cylinder pressure (and why timing get's as low as -8°, maybe lower, on a HPCR). The 24V head is more efficient than a 12V head, so what are we left on a p-pump conversions (other than conversions are not built for efficiency, but power).

[ISX]

Don't forget the more fuel you inject, the closer you get to making peak pressure at the optimal crank position. With too much timing and you end up igniting too early and create a bit of negative torque. So you are probably more efficient at 40% throttle than 10% throttle. Does that mean more mileage beating on it than not, well it might, or might not. Timing my be setup less optimally in a VP truck, but the timing is setup wrong on the p-pump trucks 99% of the time. Even the stock 14.5° of timing is only 100% ideal at near WOT at 2000 rpms ± 200 rpms. So that's not really much of an argument either. In order to reduce NOx you need to retard timing, NOx is created by high cylinder pressure (and why timing get's as low as -8°, maybe lower, on a HPCR). The 24V head is more efficient than a 12V head, so what are we left on a p-pump conversions (other than conversions are not built for efficiency, but power).

Where are you getting your figures for optimal timing vs RPM vs load? What is the optimal timing for 1700RPM 5-10% load?

[AH64ID]

I built a timing calculator that takes pulse width and rpms into account. I think tell the calculator how much fuel I want injected prior to TDC and how much after. Other than low rpm/load and cruise I run about a 50:50 split. The calc then tells me what to set the timing to. The split would be different on a single event motor (VP/Ppump) based on ignition delay being greater without a pilot, so it's not apples-apples, but apples-apple cider. A 12V p-pump will have more ignition delay than a 24V p-pump for the same mm3 and boost, because of piston design and flow differences. 5 psi of boost on a 12V is going to be less flow than 5 psi of boost on a 24V, so the 24V will see greater per-igntion cylinder pressure and temperature, and thus a quicker ignition. The calculator cannot be used on a mechanical injection truck, unless you know how long the injector is open at say 100mm3 at 2000 rpms (pressure and volume effect duration/pulse width). The way the calculator works is you tell it the %age you want injected prior to TDC. So 0% would start injecting at TDC (0.0°), 100% would finish injecting at TDC, 50% would do 50% before TDC and 50% after, 500% would injected it quite a bit before TDC (if it were a 1000us injection event then it would start 5000us prior to TDC and end 4000us before TDC), -500% would start a long time after TDC (if it were a 1000us injection event then it would start 5000us after TDC and end 6000us after TDC). The calculator knows crank and converts us to degrees of timing based on crank speed.So as an example I was running ~200% of my fuel being injected prior to TDC at cruise speed and was getting too much negative torque (pressure building before TDC), so I retarded it to ~100% and mileage went up. As fuel increases ignition delay decreases, as rpms increase ignition delay decreases, in terms of degrees but not always in us. So you need to account for that. A 50:50 split will have low timing at low fuel/rpms and high timing at high fuel/rpms, maybe a 20° difference from 10mm3 at 3000 rpms to 140mm3 at 3000 rpms.What is your advertised mm3, rated rpm, and stock timing?

[ISX]

Well heres my dilemma... Nobody can tell anyone what the timing should be on a given 12V. People say 16 for mileage and not to go over 18 or you'll blow a head gasket. I am not too sure about either one of those things... I ran advanced timing though someone set it wayyyy back when I didn't know anything I guess 3 years ago and they just assumed it was at the stock timing and popped the pump gear off and turned the engine a few degrees then put it all back together and charged me $150. The guy sure didn't confirm anything so it could have been at 20* for all I know. When he was done, it knocked (not as bad as a 24V) and had a lot of top end power, so I was happy. I didn't know the difference as to what he had done so how could I not be happy, it had power.

However, it started like crap and after talking with everyone on CF they told me that was not a characteristic of being advanced to 16, but rather a 20*+ characteristic. This thing was starting at 50F as if it were -40F out. Then I figured everything out myself and set it back to stock. The starting problem was solved but the low end power was ungodly. I couldn't believe how much I had lost. But alas, I had set it by doing some shadetree instructions on CF and when I set it again based on the injection pump pin, it was at 2* ATDC.... So I set it back to stock though I used the valve overlap to guesstimate TDC, but this appeared to get me pretty close. Then I finally figured out the valve drop absolute TDC thing and the spill port timing thing and it was pretty close to stock value IIRC, this time I set it right at 13.5* (which is the stock value actually) and I think it runs perfect.

So, back to the dilemma.... Actually you tell me what you need and if it's even possible to do this. I know injector nozzle sizes, plunger sizes, delivery valve sizes...Hell I have an entire P7100 on my desk. I don't want to burden you so if it's an issue then don't worry about it. But if it's even possible, I think you could get a formula and then make an excel such as this.

This would help the whole world since people with 4.10's and 3.55's are both following the same 16* rule even though they are 500RPM apart at the same speed and load is different too. I for one never get over 2000RPM much. Thing is there just isn't anything more than a seat of pants to tell us where to set timing.. Being static makes it worse since guys who run 3000RPM all day can't run that kind of timing since then it will start like crap. In the summer it wouldn't really make a difference and with the trailer I run at 70mph since it's always interstate and that's 2100RPM. The RPM is so high that you can just set the cruise and let it do whatever it wants and EGT is never an issue up any hill you have. But I run 1800 without it, so it would be nice to see where it needs to be in both instances.

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