then with the terms understood, a reduction in pressure does increase the physical (vs chemical) ignition delay. And timing must be advanced to compensate for this.
mm3 ???
- Thread starter walsh450mx21
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then with the terms understood, a reduction in pressure does increase the physical (vs chemical) ignition delay. And timing must be advanced to compensate for this.
In separate matrices.
pressure comes from TPS and RPM. PW comes from pressure and RPM. In turn, in their respective histograms. There is no PW until pressure is determined, there is no pressure till your foot stand on the pedal.
EFI could call it "load". That might be more realistic. as soon as they tacked on mm^3 to the number, it was defined as a solid quantity. Even if that quantity is accurate for the stock tune, the moment you touch the pressure table or PW table, it is no longer accurate. And afterall, EFI is a tool to change the tables, not keep them the same. So "mm3" is really a misnomer the first time out.
If this just isn't connecting, let's move on. It is a difficult conceptual issue, and nobody really cares anyway. :hug:
Are you talking about reduction of cylinder pressure?
Are you talking about reduction of fuel pressure?
In regards to cylinder pressure ie.. compression of air. " And timing must be advanced to compensate for this" Cylinder pressure increases heat..... How could advancing the timing help? Advancing the timing only increases further problems.
In regards to reducing fuel pressure and adding pulse width to correct quantity amount of fuel injected. " And timing must be advanced to compensate for this" Increasing timing for fuel pressure reduction has to be done only to compensate for the time required to heat the fuel to a point of flash.
Your going in the wrong direction with this one. The point is to be more efficient. Your original reason for this " lower pressure longer pulse" is for noise emissions amongst other " things ".
As far as the physical reaction ( fuel evaporation ). Your adding time to the process which increases the chemical reaction ( burn ). This only reduces noise ( your goal ), work suffers ( hp ) torque is also reduced, most of the energy to cause work is absorbed in the block, crank, pistons and rods amongst other components.
Our goal is to be efficient in tuning. Or at least gain as much power from our fuel we can. Try playing with pilot injection if you want to decrease noise. Diesel fuel requires heat to flash, as well as oxygen, lowering pressure and heat reduces this ( or increases time to for this process ). Advancing timing for very large quantities of fuel has a reason, but for small quantities reducing pressure and heat while adding timing is not efficient ( as far as cylinder pressure that is ). Your practice of lowering pressure has reduced your noise emissions, I agree, but I'm not convinced this will help any other aspect of power or mileage tuning.
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Move on. I personally could care less what it's called so long as I can follow it in the log and tune. It takes fuel to overcome the load - Right?
Unfortunately, most of my tuning experience comes from tuning LBZ ECMs. I haven't really looked at many LB7 or LLY ECMs and I have never looked at an LLM ECM, although I would guess it is closer to an LBZ than an LB7/LLY. Because of that some of my observations may be different than yours, but here's the way I see the chart flow, how they fit together and where mm3 fits in.
You start off with the torque reference to throttle position where your y-axis is throttle position, your x-axis is RPM and the data entered in the table is your torque reference number.
From there you go to the mm3 to torque reference number where your y-axis is torque reference, your x-axis is RPM and the data entered in the table is fuel in mm3.
From there you go to the base fuel pressure table where the y-axis is mm3, the x-axis is RPM and the data entered in the table is desired fuel rail pressure.
Now that you have your desired mm3 and your desired fuel rail pressure you can go to your main injection pulse table where the y-axis is fuel quantity in mm3, the x-axis is rail pressure and the data entered in the table is pulse width.
Now, theoretically, when stock this table should be accurate for how much fuel the injector should flow at x pressure for y duration. I believe when you log the main injection fuel quantity this number is shown based solely on RPM and tq. ref. If you leave the injection pulse table stock then the mm3 should be accurate, but when you change the pulse table the mm3 number is no longer going to be accurate and will only be good as a reference point in tuning.
Okay, lets say your tq. ref. number when cruising at 2000 RPM is 300 ft-lbs. Now lets say your tq. ref. table calls for 30 mm3 of fuel at 2000 RPM with 300 ft-lbs. That table has no idea how much rail pressure or even what duration is used when you are at 2000 RPM and 300 ft-lbs. If you are cruising at those numbers it will report 30 mm3 regardless of any other factors. Now if you have your pulse turned up so that it is injecting too much fuel and you have to back off the throttle, reducing the tq. ref. number, you may log a lower fuel quantity, but it isn't becuase of anything to do with your rail pressure, it is because you screwed up the pulse table and it is no longer accurate consistent for the quantity of fuel delivered in a given amount of time at a given pressure.
Now that I've said that, I know there are tables that add or take away from main injection pulse for certain positions or limit maximum quantity for different conditions, but I ignored those for simplicity's sake because, from what I've seen, those tables would have the same effect no matter what your rail pressure or pulse time is. They are usually things like ECT, IAT, Barometric Pressure, etc.
You start off with the torque reference to throttle position where your y-axis is throttle position, your x-axis is RPM and the data entered in the table is your torque reference number.
From there you go to the mm3 to torque reference number where your y-axis is torque reference, your x-axis is RPM and the data entered in the table is fuel in mm3.
From there you go to the base fuel pressure table where the y-axis is mm3, the x-axis is RPM and the data entered in the table is desired fuel rail pressure.
Now that you have your desired mm3 and your desired fuel rail pressure you can go to your main injection pulse table where the y-axis is fuel quantity in mm3, the x-axis is rail pressure and the data entered in the table is pulse width.
Now, theoretically, when stock this table should be accurate for how much fuel the injector should flow at x pressure for y duration. I believe when you log the main injection fuel quantity this number is shown based solely on RPM and tq. ref. If you leave the injection pulse table stock then the mm3 should be accurate, but when you change the pulse table the mm3 number is no longer going to be accurate and will only be good as a reference point in tuning.
Okay, lets say your tq. ref. number when cruising at 2000 RPM is 300 ft-lbs. Now lets say your tq. ref. table calls for 30 mm3 of fuel at 2000 RPM with 300 ft-lbs. That table has no idea how much rail pressure or even what duration is used when you are at 2000 RPM and 300 ft-lbs. If you are cruising at those numbers it will report 30 mm3 regardless of any other factors. Now if you have your pulse turned up so that it is injecting too much fuel and you have to back off the throttle, reducing the tq. ref. number, you may log a lower fuel quantity, but it isn't becuase of anything to do with your rail pressure, it is because you screwed up the pulse table and it is no longer accurate consistent for the quantity of fuel delivered in a given amount of time at a given pressure.
Now that I've said that, I know there are tables that add or take away from main injection pulse for certain positions or limit maximum quantity for different conditions, but I ignored those for simplicity's sake because, from what I've seen, those tables would have the same effect no matter what your rail pressure or pulse time is. They are usually things like ECT, IAT, Barometric Pressure, etc.
Ignition delay is related to fuel pressure for one reason. Evaporation. The flash point you refer to, or point of combustibility, is going to dependent (among other things) on how long it takes for enough diesel to evaporate to an ignitable mix. Temp is not an issue, our compression rates insure that.
With lower fuel pressure, a coarser spray enters the hot charged cyclinder. At this point the cylinder is ballpark 1100F, several hundred degrees above the auto-ignition temp required. The coarser spray has larger droplet diameters, and fewer of them. This is a reduced fuel/air surface area ratio than when injected under higher pressure. The lower SA intrface, reduces the evaporation rate, and the ignition delay. As a result of the extra delay, to maintain optimum ignition timing must be advanced to provide the extra time needed for evaporation, and still maintain the optimum LPP (location of peak pressure, typically 5-14 atdc, rpm dependent).
FWIW, i didn't say that lowering pressure increased BMEP. In theory it doesn't but I don't have instrumentation to verify it. What I do have is a truck that is as quiet as a Lexus on the highway, and gets over 20 mpg. That could probably be increased, but economy (efficiency) is one of 3 or 4 elements that gets juggled at the expense of the others.
With lower fuel pressure, a coarser spray enters the hot charged cyclinder. At this point the cylinder is ballpark 1100F, several hundred degrees above the auto-ignition temp required. The coarser spray has larger droplet diameters, and fewer of them. This is a reduced fuel/air surface area ratio than when injected under higher pressure. The lower SA intrface, reduces the evaporation rate, and the ignition delay. As a result of the extra delay, to maintain optimum ignition timing must be advanced to provide the extra time needed for evaporation, and still maintain the optimum LPP (location of peak pressure, typically 5-14 atdc, rpm dependent).
FWIW, i didn't say that lowering pressure increased BMEP. In theory it doesn't but I don't have instrumentation to verify it. What I do have is a truck that is as quiet as a Lexus on the highway, and gets over 20 mpg. That could probably be increased, but economy (efficiency) is one of 3 or 4 elements that gets juggled at the expense of the others.
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My previous post says this but not in the same words. I must also add that as the fuel is sprayed it begins to burn and adds to the low pressure issue.
The only thing I hear from my truck is a little road noise at highway speeds and the turbo occasionally at hills and bridges. Sounds like there is more than one way to keep a truck quite.
Thank you for the conversation, it was fun.
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I would say fortunately we have you and your lbz tuning knowledge. With your experience tuning the lbz, and mine with the lly and lb7, we should start a couple of threads in the tuning section labeled as these and teach one another our style of tuning. We may also learn a great deal from other tuners as they chime in. Hopefully someone will add the lmm to the list.
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yes it was fun. 
Thanks! Somebody should start a general timing consideration thread. Maybe we could learn something about realistic timing expectations and effects on optimized torque production.
Thanks! Somebody should start a general timing consideration thread. Maybe we could learn something about realistic timing expectations and effects on optimized torque production.
I am planning to add a pressure sensor in one of my spark plug holes to log just that.
It took me many attempts to figure out on how to make the engine more quiet as I could not find any logged data which corresponds to the noise.
It took me many attempts to figure out on how to make the engine more quiet as I could not find any logged data which corresponds to the noise.
maybe you were using the wrong spark plugs :joker:
seriously, would love to see how that works out for you. Is there an existing transducer for this application? Have you figured out how you will interface it with EFI?