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Thread: Thoughts on Tuning and the LNF.

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    Thoughts on Tuning and the LNF.

    Here is my contribution to the LNF tuning thread. Contained in this thread are my thoughts on tuning and the LNF. I have posted smilar threads on other forums but I can expand on this information more on here than other forums without going right over people's heads with information so if anyone has a specific question to ask me please do so I can go more in depth. I hope you guys like this. I wrote this many months ago and I can add to this if anyone want to ask me for more info on any specific subject. Because I know I may have missed a few things LOL.

    The Gasoline Direct Injection (GDI) LNF uses a Bosch E69 GDI ECM. This ECM is a torque based engine controller containing approximately 2,500 tables that control all engine functions. There are approximately 600 tables that control fueling alone. A typical ECM contains only approx 250 tables total by contrast which is why a read entire takes about 10 times as long as most ECMs. A Gasoline Direct Injection (GDI) based fuel injection system is much harder to control and optimize than a typical Multiport EFI system which is why there are so many total tables In the ECM and so many that control fueling.

    At the heart of this ECM is its torque based control system that uses driver input via pedal position to determine driver desired torque. Think of it as 100% pedal is equal to 100% driver desired torque. The driver desired torque value is fed into the Desired Airload table (DAL) which uses driver desired torque (pedal position) vs RPM to determine actual throttle postion. By raising or lower the DALs one can effect how the car reacts to pedal input from the driver. You can make 50% pedal 100% actual throttle opening or vise versa by raising or lowering those values. The DALs are regulated by the Maximum Airload Torque table (MALT) whch determines the percentage of actual airload allowed based on RPM. The Combination of the DAL and MALT helps determine actual throttle postion and does regulate the wastegate to some degree but does not allow for the desired boost level to be raised above 238 kPa, 34.5 psi absolute or 20 psi guage without modifying another table that we HP Tuners users do not yet have access to.

    The GM stage tune rasies this desired boost ceiling to 255 kPa, 37 psi absolute or 22.5 psi gauge using the same Desired airloads one would normally to acheive 238 kPa. The Superchips Tune also raises the desired boost levels without changing the desired airloads. Which proves there are more boost control tables than DAL and MALT.

    There is debate as to what is proper as far as what is Air to Fuel (A/F) mixture is appropriate for the LNF while in Power Enrichment Mode (PE) at Wide Open Throttle. PE ratios are expressed as Lambda where 1.00 Lambda = 14.69 A/F mixture when using gasoline. The Stock GM Tune and Stage one tune both use the same PE ratios of 0.95 to 0.87 lambda (14.0-12.8 A/F) I have seen anywhere from 11.4 to 14.0 PE A/F used depending on the tuner. I personally believe that the most effective A/F range for the LNF is 0.86-0.92 Lambda (12.6-13.2 A/F). PE lambda is influenced by Power Enrichment VS Time which is better known by most as the catalyst overtemp protection table or COT Lambda table. After a certain time at WOT once the ECM models a catalyst temperature of 1700* the ECM will richen the A/F mixture to as rich as 0.711 Lambda or 10.45 A/F at WOT. Most change those values to match their PE Lambda Table or if they are catless they set all values to 1.00 lambda to disable the extra enrichment.

    Ignition and cam timing is another aspect of tuning this ECM as the LNF has variable valve timing. The VVT is controlled by cam phasers on each camshaft. The LNF has 4 sets of basic timing tables based on load, RPM, and Camshaft postion in relation to each cam's minimum and maximum states. Although there are more timing tables these are the main ones we are concerned with. Timing theories vary according to application but there is one universal truth. There is a point at which adding more ignition timing will actually cause torque and conversely HP loss which is normally but not necessarily due to knock retard. There is always a sweet spot where the mixture burns completely and just at the right time so that maximum cylinder pressure is reached right as the piston comes to Top Dead Center (TDC). That results in the the most work possible being performed on the piston (Large Force Acting on the piston for the most time possible) and hence the most torque output possible at that RPM. If the mixture burns too long from running too much ignition timing it will reach peak cylinder pressue well before TDC and the results will be spark knock and power loss, but if there is too little ignition timing run the mixture will not have sufficient time to burn completely and peak cylinder pressure will be reached after the piston passes TDC and the result will be less torque produced (Smaller Force acting on the piston for less time) The LNF is no different. It uses less WOT timing than any other engine I have ever seen partly do to the efficiency of the Direct Injection which produces much better fuel atomization and the comparatively lean mixtures GDI cars are known to run at WOT. Lean mixtures burn faster and hotter and require less timing because they burn quickly. Rich mixtures burn slower and at lower temperature and require more timing to burn completely.

    There are over 20 camshaft tables but the only ones most would modify are the Intake Cam Main Warm table and the Exhaust Cam Main Warm Table. Many have wondered what the units in those tables are as they are undefined in HP Tuners. They are based on the camshaft's base circle. As I understand, the units influence how many degrees from center the camshaft is based on its base circle. So it is the camshaft itself that gives meaning to those units. That is why the values in the scanner are so much different than the values in the tables themselves and why it is possible to have a negative value in the table but a positive value in the scanner. Some have found small gains in top end HP by advancing the intake cam 2-3* in the upper RPM and upper load regions of that table. When you advance the intake or the exhaust cam you are asking it to open sooner. The theory behind a slight advance in intake cam timing is to open the intake valve a little sooner so the cylinder can take in more air on the intake stroke. Exhaust cam tuning theory is the opposite principle. You want to leave the exhaust valve shut as long as possible so that maximum cylinder pressure is reached before the exhaust valve opens. The problem is if you wait too long to open the exhaust valve peak cylinder pressure already have been reached before the exhaust valve opens. That means either knock will ensue or the piston will already be past TDC and the ability to generate peak torque will be lost. If the exhaust valve opens too soon (too much advance) peak cylinder pressure cannot be acheived before the exhaust valve opens and cylinder pressure loss and conversely power loss will ensue. Ignition timing and valve timing are inextricably intertwined as they have direct influence on one another. For example, advancing ignition timing coupled with retarding the exhaust valve timing will work togther to increase cylinder pressure but too much ignition advance or too much exhaust valve retard will be counter productive as it will likely result in knock retard.

    The "Learn Down" feature. Because the LNF's ECM uses torque based controls it is much more advanced as far as limiting or adding to the torque that is desired from it. All modern ECMs that I have seen have Torque Management (TM) tables, and the LNF is no exception, but its entire engine management system is built around Driver Desired Torque vs Actual Torque Output. Driver desired torque is based on Pedal Position, RPM, Desired Airload, and Maximum Airload Torque. Those values determine Optimum Engine Torque which calculates engine torque output based on 1.00 Lambda. The Lambda Efficiency table changes calculated engine torque based on A/F Ratio expressed as Lambda. Leaner than 1.00 Lambda will produce less actual torque, and richer than 1.00 Lambda (up to a point) will produce more actual torque output. The "Learn Down" that most notice occurs when adding mods or driving in very cold weather they notice the boost pressure values have gone down. The ECMs torque based controls are to blame for this. If breathing efficiency is increased either from adding mods or from a denser air charge the ECM compensates for this by decreasing its Desired Boost pressure values. It does so because Actual Torque Output is modeled as greater than Desired Torque output. The GM Stage 1 tune raises the Desired Boost and Actual Torque output levels but does NOT completely remove the learn down but it does raise it. Other Tunes work the same way. They do not completely remove the learn down they merely raise it to a level that the car cannot acheive in the first place. Think of the learn down more like a target airload level or target torque output level. If you add mods or change the charge air density the ECM will sense that it is reaching its target torque output much more easily than before. That is not to say that adding mods without a tune will produce no gains at all. It is possible when adding mods like a catless DP and an Intake to make more power than stock even without being retuned. Although the gains are much larger if you retune the car I have seen evidence that even thousands of miles after adding mods a car will still dyno higher than stock. I have seen a stock tune LNF with an Intake and Catless DP make 254 whp and 272 wrtq thousands of miles after first adding the mods. That car stock on that same dyno would made 243 whp and 251 wrtq.
    Last edited by Terminator2; 09-03-2010 at 02:06 PM.

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    Senior Tuner Iam Broke's Avatar
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    Very nice contribution, thanks.

    Can you write up a paragraph explaining how the Stoich value of adding Ethanol changes the fueling trims and the method we use to compensate for it (since we have no stoich tables) and how it relates to the MAF lb/min airflow logged?
    '12 Camaro T3 2SS/RS LS3 M6, SLP TVS 2300, Flex Fuel

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    Quote Originally Posted by Iam Broke View Post
    Very nice contribution, thanks.

    Can you write up a paragraph explaining how the Stoich value of adding Ethanol changes the fueling trims and the method we use to compensate for it (since we have no stoich tables) and how it relates to the MAF lb/min airflow logged?
    Sure will. I will add it in a few minutes.

    Ok first post is too many charactors so I have to make a 2nd post already LOL. Continuing on:

    Tuning the LNF for Ethanol Based fuels (E-85 or a blend of E-85 and gasoline).

    Tuning for ethanol based fuels with your LNF will require you to know a few basic facts. First of all, the LNF has a wideband A/F meter and it operates in closed loop (sensors send feedback on A/F mixture) even during WOT where narrow band equipped cars will go into open loop (sensors do not send feedback on A/F mixture). The second bit is that the WB reads in lambda not A/F (This fact becomes important later). It is also important to understand stoichiometry (Stoich means element, metry means measure) Stoichiometry refers to the measure of products and reactants in a chemical reaction. Here we are discussing a combustion reaction. Here for our purpose stoichiometry (stoich) is used to express the ratio of Air to Fuel in the combustion reactions. Stoich values differ according to the fuel used for example, Stoich for gasoline is approximately 14.7 parts air to every one part fuel (14.7:1) Stoich for 100% ethanol is approx 9.0:1 and stoich for E-85 is 9.7:1. The reason stoich is so much richer for alcohol based fuels is due to the oxygen containing hydroxyl group (-OH) Because alcohols contain extra oxygen less atmospheric oxygen is required to properly combust the mixture. Because we have no table in HP Tuners that we can use to change stoich values we have to use another method to tune for the ethanol. Is it the best or easiest method to use? No, but luckily, we have that wideband that is constantly reporting because it makes it so much easier. We have to use MAF tuning for now to bring the fuel trims and the overall A/F back where it belongs. In order to compensate for extra oxygen in the Ethanol when it is first added and no tuning has been done the ECM moves the long term fuel trim in positive direction as it senses a lean condition which signals the injectors to lenghen their pulse width. Going from strait gasoline to E-85 will trigger approximately +30% change in in the LTFTs. This will trigger a MIL as the LTFT shows an excessively lean condition has occured. To correct this the whole MAF calibration tables has to be multiplied by 1.3 to bring the LTFTs back close to 0. When we make this 30% change we skew the MAF's readings by 30% (30lbs/min actual flow becomes 39 lbs/min measured) as we are tricking the MAF into thinking it is seeing 30% more air than it actually is to correct the A/F for the E-85. Remember when I said the WB reading in Lambda was important? Here is why. 1.00 Lambda is always equal to stoich no matter what type of mixture of fuels is used. So 1.00 Lambda is 14.7 A/F for gasoline 9.7 A/F for E-85 and 9.0 for E-100. This makes it so much less confusing then trying to figure out which PE A/F to run and makes conversions very simple. So 1.00 lambda always equals stoich no matter what which makes PE lamba very easy to figure out as well. For example using 0.88 PE Lambda for both gasoline and E-85 For gas 1.00 Lambda = 14.7 A/F so that means 0.88 Lambda equals 14.7 X 0.88 = 12.9 A/F. Many of us are very familar with this simple conversion but it also applies here with E-85 where 1.00 Lambda = 9.7 A/F so 0.88 X 9.7 = 8.5 A/F. Seems really rich doesn't it? Well it is, but this is the effect of running E-85 in this or any car it will run 30% richer and gas mileage can suffer up to 30% as a result so If you were getting 30 MPG on gasoline you can expect 21-22 MPG on E-85.
    Last edited by Terminator2; 09-03-2010 at 03:07 PM.

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    Great write up Term, thanks bud.

    Curious to know whether or not there are any specific tables associated with the ETC or if it's embedded into multiple tables?
    09 RY Cobalt SS Coupe - 19K miles - Bolt ons + 7163 ZFR, HP tuned on ethanol

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    Quote Originally Posted by T-Man View Post
    Great write up Term, thanks bud.

    Curious to know whether or not there are any specific tables associated with the ETC or if it's embedded into multiple tables?
    I do not know for sure yet. I am sure there is a torque management pedal % vs ETC %.

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    Anyone have any other questions? I am so bored at work today. So slow because everyone assumes we are closed.

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    What are you doing at work on Labor Day? Even I'm off!
    '12 Camaro T3 2SS/RS LS3 M6, SLP TVS 2300, Flex Fuel

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    both of my jobs are open today but I'm only working 1. term, great writeup, it helps to make people understand what things mean opposed to do this do that and now your tuned lol. it doesn't help a lot with the tuning aspect but definatly is explainatory.

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    Quote Originally Posted by Jaxon View Post
    both of my jobs are open today but I'm only working 1. term, great writeup, it helps to make people understand what things mean opposed to do this do that and now your tuned lol. it doesn't help a lot with the tuning aspect but definatly is explainatory.
    Yep, It is meant to be different than Nick's thread. It explains how everything works and tuning theory rather than saying "do this" to tune the car. It will help people understand why they are doing this rather than "this is what you do" and you have no idea why or how it works. Do you have any tuning theory questions?

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    Quote Originally Posted by Iam Broke View Post
    What are you doing at work on Labor Day? Even I'm off!
    My dad is a slave driver.

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    Quote Originally Posted by Terminator2 View Post
    My dad is a slave driver.
    '12 Camaro T3 2SS/RS LS3 M6, SLP TVS 2300, Flex Fuel

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    my used hpt should be here soon!

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    Great thread. It helps you understand what's going on in the LNF ECU as well as just general engine managment as well.

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    Thanks guys. If anyone has specific questions do not hesitate to ask.

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    Thanks for the read. Lots of great info. I've been tuning my car for a while now but haven't posted much because I'm trying to still get everything down before trying anything to crazy. I do appreciate everyones input and hopefully the future will just get better for these cars.

    The only question I've been wondering about is how well do the tables we have work for a turbo swap? I know a wastegate control would be awesome but how much different is it controling a different turbo with the mal table? Or is there is a difference? And input is awesome although I'm not sure how many turbo swapped cars you guys have been able to mess with. Thanks in advance guys
    Ryan

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    Quote Originally Posted by Ryans09SS/TC View Post
    Thanks for the read. Lots of great info. I've been tuning my car for a while now but haven't posted much because I'm trying to still get everything down before trying anything to crazy. I do appreciate everyones input and hopefully the future will just get better for these cars.

    The only question I've been wondering about is how well do the tables we have work for a turbo swap? I know a wastegate control would be awesome but how much different is it controling a different turbo with the mal table? Or is there is a difference? And input is awesome although I'm not sure how many turbo swapped cars you guys have been able to mess with. Thanks in advance guys
    Ryan
    The turbo swapped cars will respond differently if a different size WG spring is used. For example our stock WG spring is 5 lbs. If you had a 10 lb spring on your aftermarket turbo the DALs and MALT are going to be more sensitive so what settings were used to acheive lets say 20 psi would be more likely to hit closer to 25 psi with a different size WG spring.

  17. #17
    Re-hashing an old post, yes, but I figured I'd keep it all in the same place.

    Got a couple questions for you, Term.

    1. What exactly in a tune for LNF's is making all the power? I assume it's mostly lowering PE lambda and raising ignition timing in those same spots that lambda has been increased to create more pressure within the combustion chamber while still keeping the a/f mix from detonating before TDC. I know that will create power in an NA engine, but how does boost from the turbo play into this whole mess?

    2. Tuning for bolt-ons. What sort of tuning (if any) can be done for bolt-on parts such as aftermarket intakes. Are they mostly just to allow the engine to build the power it is looking for with more ease? Or is there a method to use these to our advantage and build more power because of these replacement parts?

  18. #18
    Quote Originally Posted by Ch1ck3n View Post
    Re-hashing an old post, yes, but I figured I'd keep it all in the same place.

    Got a couple questions for you, Term.

    1. What exactly in a tune for LNF's is making all the power? I assume it's mostly lowering PE lambda and raising ignition timing in those same spots that lambda has been increased to create more pressure within the combustion chamber while still keeping the a/f mix from detonating before TDC. I know that will create power in an NA engine, but how does boost from the turbo play into this whole mess?

    2. Tuning for bolt-ons. What sort of tuning (if any) can be done for bolt-on parts such as aftermarket intakes. Are they mostly just to allow the engine to build the power it is looking for with more ease? Or is there a method to use these to our advantage and build more power because of these replacement parts?
    I am not Term, but I think I can answer these questions for you.

    1. The DAL and MAL are what control the bulk of the power in the LNF. The DAL and MAL basically "limit" the amount of air that can enter the CC, therefore limiting the amount of power/torque that can be achieved. The stock tune on the LNF is typically lean and most people richen the PE lambda. Some of the LNF respond better to increased timing than others.

    2. Most of the LNF bolt-ons help boost come on faster or hold better. You may see some small HP/TQ increases but the majority of power is still limited by the DAL and MAL. With some bolt-ons it makes it "safer" to raise the DAL and MAL to higher limits as well as getting a catless downpipe and removing COT. Changing the LNF intake will almost always require tuning the fuel trims.

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    Ok, here's a discussion point that i've seen elsewhere as well. Why use the "MAF Calibration" table to adjust for E85, knowing that it will throw your airflow readings out of wack? I thought the point of that table was to make adjustments when there is an airflow track change to get the most accurate airflow readings possible. Why not use the "MAF correction" table to adjust for E85? We have a two-fold factor of increase in that table, so the 30% needed off the bat is no problem. I personally try to leave the calibration table alone when tuning fuel trims, since i have the stock airbox in place. That included tuning my water/methanol injection set up.
    2013 Cruze Eco - CAI, Catless DP, Catless MP, ZZP FMIC, Ported Intake Manifold, Mild tune (17psi), best 43.5mpg, 175ftlbs (pid)

    2008 Solstice GXP - ZFR 6758, catless, AEM stage 1 water/methanol injection, Hahn Racecraft Intercooler, solo street race cat back, LE5 throttle body - 307whp on a dyno dynamics (stock turbo numbers), 100 octane EFR6758 numbers - 463whp/454wtq

  20. #20
    Senior Tuner Iam Broke's Avatar
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    Interesting thought, hadn't tried it. I just use the VE airflow to gauge performance.
    '12 Camaro T3 2SS/RS LS3 M6, SLP TVS 2300, Flex Fuel