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SVTPerformance's Chain of Restaurants
Tuning À la carte
Is Your Car Tuned Correctly?
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<blockquote data-quote="eficalibrator" data-source="post: 12517978" data-attributes="member: 33592"><p>Gentlemen,</p><p></p><p>As much as I enjoy seeing science posted (especially if I am the one being referenced!), it's important to avoid showing only that part that may be convenient to one's underlying cause. I won't get dragged into the "who's a better tooner" debate, so I'll stick to some facts about calibration.</p><p></p><p>1) Given an EXACT maf curve from a certified flow bench, I would prefer to use it in the calibration and not touch it. The trick here is that you must believe the calibration of the bench and make sure you test the entire inlet system from filter to throttle body if you want 100% accurate data. This is often just not an option in the aftermarket. Testing only the MAF housing and then installing it at a different angle, pipe layout, or location negates all that good work and just has you working based on bad ASSumptions. Be careful, but it can save a lot of time later if this is correct in the beginning.</p><p></p><p>2) Solving for MAF on a running engine is still a valid method. It doesn't matter if you're working toward a MAF sensor transfer function or a VE table, the science is IDENTICAL. However, this has a few requirements that MUST be correct if you are to get good data. You MUST know fuel flow. In an OEM engine dyno lab, we have fuel flow meters on the line feeding the engine and a set of exactly nominal fuel injectors that were hand selected from the supplier. If you know the exact relationship between ms of injector pulsewidth and mg of fuel delivery on that shot, you can effectively use the injectors to "meter" the fuel flow by monitoring INJPW. Incidentally, we have fuel injector flow test standards just the same as we do for the MAF. Anyone looked at SAEJ1832 recently?</p><p></p><p>Simply put: (fuel flow)*AFR = MAF <---Anybody want to challenge this?</p><p></p><p>As long as you have valid fuel flow assumptions, you can indeed solve for MAF, g/cyl or VE on the fly. This makes the "aftermarket" method acceptable as long as you start with good fuel flow data, which MUST include proper injector data for both linear and non-linear flow ranges as well as offset compensation for both voltage and pressure. So many guys miss this and just start tooning with bad ASSumptions about cheap injectors and bake errors into the MAF or VE.</p><p></p><p>3) As I mentioned above, injectors can be just as variable as the cold air kit/MAF placement. Yes, random production injectors can be all over the place on flow. The factory tolerance is +/-6%! This is why I strongly recommend starting with good known flow matched injector sets on high performance applications. In many cases, there is a valid argument for adjusting injector slopes in a vehicle calibration, but starting with flowed/characterized injectors prevents this just the same as a flow bench does for the MAF and intake assembly.</p><p></p><p>If you know the MAF data from the bench, and the fuel injector data from a bench, chances are that you don't have much work at all to do when the engine calibration is performed. We don't usually get this lucky in the aftermarket. It currently seems that injector data is a little easier to get from a good supplier (take Injector Dynamics, for example) than MAF curves for your unique vehicle intake. So the calibrator needs to figure out where he thinks the errors lie and recalibrate the ECU accordingly.</p><p></p><p></p><p>So what does this mean?</p><p></p><p>It means that there is indeed more than one valid calibration method. However, both methods (if they're done right) should come to the SAME solution. <strong>That's right, you should end up with the same MAF transfer function whether it was derived on a certified flow bench or if it was solved for in the vehicle as long as the other assumptions were properly addressed.</strong> If you get the "right" MAF curve either way, load is by definition correct, and so is the torque model (all else being correct). On a modified car, you will still need to do plenty of ETC control calibration, but all of that cannot even start until you have confidence in your MAF reading and load calculation.</p><p></p><p>I've lost count of how many engines I have tuned either way. The trick is to follow the rules and make sure you are aware of your "knowns" in either case. Properly done, changes in weather or baro should not alter AFR control, knock control, driveability, or ETC safety.</p><p></p><p>Greg Banish</p><p>Calibrated Success, Inc.</p></blockquote><p></p>
[QUOTE="eficalibrator, post: 12517978, member: 33592"] Gentlemen, As much as I enjoy seeing science posted (especially if I am the one being referenced!), it's important to avoid showing only that part that may be convenient to one's underlying cause. I won't get dragged into the "who's a better tooner" debate, so I'll stick to some facts about calibration. 1) Given an EXACT maf curve from a certified flow bench, I would prefer to use it in the calibration and not touch it. The trick here is that you must believe the calibration of the bench and make sure you test the entire inlet system from filter to throttle body if you want 100% accurate data. This is often just not an option in the aftermarket. Testing only the MAF housing and then installing it at a different angle, pipe layout, or location negates all that good work and just has you working based on bad ASSumptions. Be careful, but it can save a lot of time later if this is correct in the beginning. 2) Solving for MAF on a running engine is still a valid method. It doesn't matter if you're working toward a MAF sensor transfer function or a VE table, the science is IDENTICAL. However, this has a few requirements that MUST be correct if you are to get good data. You MUST know fuel flow. In an OEM engine dyno lab, we have fuel flow meters on the line feeding the engine and a set of exactly nominal fuel injectors that were hand selected from the supplier. If you know the exact relationship between ms of injector pulsewidth and mg of fuel delivery on that shot, you can effectively use the injectors to "meter" the fuel flow by monitoring INJPW. Incidentally, we have fuel injector flow test standards just the same as we do for the MAF. Anyone looked at SAEJ1832 recently? Simply put: (fuel flow)*AFR = MAF <---Anybody want to challenge this? As long as you have valid fuel flow assumptions, you can indeed solve for MAF, g/cyl or VE on the fly. This makes the "aftermarket" method acceptable as long as you start with good fuel flow data, which MUST include proper injector data for both linear and non-linear flow ranges as well as offset compensation for both voltage and pressure. So many guys miss this and just start tooning with bad ASSumptions about cheap injectors and bake errors into the MAF or VE. 3) As I mentioned above, injectors can be just as variable as the cold air kit/MAF placement. Yes, random production injectors can be all over the place on flow. The factory tolerance is +/-6%! This is why I strongly recommend starting with good known flow matched injector sets on high performance applications. In many cases, there is a valid argument for adjusting injector slopes in a vehicle calibration, but starting with flowed/characterized injectors prevents this just the same as a flow bench does for the MAF and intake assembly. If you know the MAF data from the bench, and the fuel injector data from a bench, chances are that you don't have much work at all to do when the engine calibration is performed. We don't usually get this lucky in the aftermarket. It currently seems that injector data is a little easier to get from a good supplier (take Injector Dynamics, for example) than MAF curves for your unique vehicle intake. So the calibrator needs to figure out where he thinks the errors lie and recalibrate the ECU accordingly. So what does this mean? It means that there is indeed more than one valid calibration method. However, both methods (if they're done right) should come to the SAME solution. [B]That's right, you should end up with the same MAF transfer function whether it was derived on a certified flow bench or if it was solved for in the vehicle as long as the other assumptions were properly addressed.[/B] If you get the "right" MAF curve either way, load is by definition correct, and so is the torque model (all else being correct). On a modified car, you will still need to do plenty of ETC control calibration, but all of that cannot even start until you have confidence in your MAF reading and load calculation. I've lost count of how many engines I have tuned either way. The trick is to follow the rules and make sure you are aware of your "knowns" in either case. Properly done, changes in weather or baro should not alter AFR control, knock control, driveability, or ETC safety. Greg Banish Calibrated Success, Inc. [/QUOTE]
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