Yet another theory on how to tune...
Ive thought about using 100% MAF at times, but was worried about low speed problems with big cams and such. Also worried about reversion.
If one scews IFR, then it messes with IDC, right?
If one scews IFR, then it messes with IDC, right?
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If you screw with IFR, is it truly wrong? IDK. I go back and forth some days. Rumor has it that the guy who tuned my dad's car used to work for GM on the PCM's (according to some of the Vette guys who met him). If that's true, I'd have a hard time taking credibility away from him and his 100% MAF/IFR approach.
As for me, I'm going to stick with tweaking the MAF curve (with the right IFR for my injectors) for the next couple of weeks to see just how close I can get things. There's still an AFR variance with IAT's. I'll probably need to move to COS#5 to deal with that. But, at least now I can keep things a little more consistent when logging with the relocated IAT.
On a side note, it was raining pretty good this morning and I was behind quite a few rooster tails on the highway. I popped the hood when I got to work and there wasn't a drop of water near the IAT - bone dry. So, it looks like I picked a good spot.
As for me, I'm going to stick with tweaking the MAF curve (with the right IFR for my injectors) for the next couple of weeks to see just how close I can get things. There's still an AFR variance with IAT's. I'll probably need to move to COS#5 to deal with that. But, at least now I can keep things a little more consistent when logging with the relocated IAT.
On a side note, it was raining pretty good this morning and I was behind quite a few rooster tails on the highway. I popped the hood when I got to work and there wasn't a drop of water near the IAT - bone dry. So, it looks like I picked a good spot.
Last edited by SSpdDmon; Jul 11, 2007 at 12:27 PM.
Originally Posted by Country Boy
Ive thought about using 100% MAF at times, but was worried about low speed problems with big cams and such. Also worried about reversion.
If one scews IFR, then it messes with IDC, right?
If one scews IFR, then it messes with IDC, right?
I've tried setting the MAF bias VERY low like said the first post but it's given me a fit with bigger cams. I hate to give away methodology and what-not, but for N/A, I move the MAF bias down to 1800-2200 and tune the VE up to about 2K and calibrate the MAF.
Don - what I don't understand is, if you are working the MAF anyway, why not build in the numbers that drive the trims negative there rather than IFR?
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Originally Posted by Frost
I've tried setting the MAF bias VERY low like said the first post but it's given me a fit with bigger cams. I hate to give away methodology and what-not, but for N/A, I move the MAF bias down to 1800-2200 and tune the VE up to about 2K and calibrate the MAF.
Don - what I don't understand is, if you are working the MAF anyway, why not build in the numbers that drive the trims negative there rather than IFR?
Don - what I don't understand is, if you are working the MAF anyway, why not build in the numbers that drive the trims negative there rather than IFR?
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Justs a side note to this. I tested the Many baffle and lid combinations out there. the SLP lid with the smooth bellows produced the best curve fit to factory the least amount of signal noise. I did test for HP. With and without lid. Made no difference on engine upto 400ci and well over 550 flywhl hp. This was all done using the plastic 85mm mafs in there various configuarations. the metal 3 pins where within 2-3hp of the plastics on engine up to 347ci at 500flywheel the error range of the dyno.
Originally Posted by SSpdDmon
Because of the theory that GM did extensive research on MAF flow meaning the MAF table is right and doesn't need to be touched. Problem is, I don't know many people running a factory lid (baffles and all) with their H/C setup. The next question is, if the curve is so accurate in factory form, why not put the factory intake assembly back on the car. Then, you'd have a safe, consistent setup at the expense of 10hp - not to mention another element of stealth.
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From: Commerce Twp, MI
Originally Posted by LS1curious
Justs a side note to this. I tested the Many baffle and lid combinations out there. the SLP lid with the smooth bellows produced the best curve fit to factory the least amount of signal noise. I did test for HP. With and without lid. Made no difference on engine upto 400ci and well over 550 flywhl hp. This was all done using the plastic 85mm mafs in there various configuarations. the metal 3 pins where within 2-3hp of the plastics on engine up to 347ci at 500flywheel the error range of the dyno.
Idle Frequencies: Had to add ~3% to keep AFR at 14.5~15:1.
Low TPS (3250~4250Hz): Had to pull 6~8% out of the curve to keep AFR at 14.5~15:1 or it would run too rich.
Moderate TPS (4500~6500Hz): Varies from -4%~4% to maintain stoich AFR.
Heavy/WOT TPS (>6500Hz): Varies from 4%~11% to get commanded AFR to equal WBO2 AFR.
That's a 20% variance! Any reason why?
Originally Posted by SSpdDmon
If you screw with IFR, then the calculation of IDC is messed with (can't be accurately calculated).
yes, but ultimately the amount of fuel dumped (fuelmass) is IPW*IFR, so people who screw with IFR effectively screw with IPW, so the IDC will change. that's why i'm so **** about getting the IFR absolutely as close to reality as possible. without real IFR you'll never know how hard your injectors are working, and that might end badly if they're underreporting.
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Originally Posted by RedHardSupra
yes, but ultimately the amount of fuel dumped (fuelmass) is IPW*IFR, so people who screw with IFR effectively screw with IPW, so the IDC will change. that's why i'm so **** about getting the IFR absolutely as close to reality as possible. without real IFR you'll never know how hard your injectors are working, and that might end badly if they're underreporting.
Originally Posted by RedHardSupra
ok, so what's your theory? just please back it up with more than 'others do it and it works fine'
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From: Commerce Twp, MI
Originally Posted by NicD
IFR is irrelevant. Injector duty cycle is calculated with the end result of the fueling, IPW vs RPM. It doesn't matter how it got there and surely not calculated with IPW*IFR. Making a car run with a 12.5 a/f through a WOT run using different methods (like changing IFR, then skewing MAF or PE tables or whatever) doesn't change your duty cycle. I thought this was pretty basic stuff.
Formula : IPW*RPM/1200=IDC%
I think we like the PCM to have the right information so we can make it easier to figure things out (i.e. when we're using custom pids) or for future mods, because in theory it should be an easier re-tune.
Last edited by SSpdDmon; Jun 19, 2007 at 02:21 PM.
ah yes, if you cut both IFR and MAF/VE tables in half then yes, i thought you're talking about IFR alone since you said IFR is irrelevant.
however, even if IDC will be right, your airmass would be halved too, so all your timing, and any other load based stuff like trans would be wrong.
IFR does matter. it only describes changes in fueling according to MAP changes. if you do a tune only with IFR you basically choose to ignore changes from other factors like temps and RPM. can you honestly tell me that you can tune a car saying that 100kPa MAP will demand the same fueling at 1000RPM and 6000RPM? there's a lot more factors here, that's why VE has both MAP and RPM axis, not just load.
however, even if IDC will be right, your airmass would be halved too, so all your timing, and any other load based stuff like trans would be wrong.
IFR does matter. it only describes changes in fueling according to MAP changes. if you do a tune only with IFR you basically choose to ignore changes from other factors like temps and RPM. can you honestly tell me that you can tune a car saying that 100kPa MAP will demand the same fueling at 1000RPM and 6000RPM? there's a lot more factors here, that's why VE has both MAP and RPM axis, not just load.
Originally Posted by SSpdDmon
I think we like the PCM to have the right information so we can make it easier to figure things out (i.e. when we're using custom injector duty cycle pids).
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Originally Posted by NicD
Why would you need to have a custom injector duty cycle pid when the standard IDC in the scanner is always correct no matter how skewed the program may be?
Originally Posted by RedHardSupra
ah yes, if you cut both IFR and MAF/VE tables in half then yes, i thought you're talking about IFR alone since you said IFR is irrelevant.
however, even if IDC will be right, your airmass would be halved too, so all your timing, and any other load based stuff like trans would be wrong. .
however, even if IDC will be right, your airmass would be halved too, so all your timing, and any other load based stuff like trans would be wrong. .
Originally Posted by RedHardSupra
IFR does matter. it only describes changes in fueling according to MAP changes. if you do a tune only with IFR you basically choose to ignore changes from other factors like temps and RPM. can you honestly tell me that you can tune a car saying that 100kPa MAP will demand the same fueling at 1000RPM and 6000RPM? there's a lot more factors here, that's why VE has both MAP and RPM axis, not just load.
Originally Posted by SSpdDmon
It's a calculated pid in EFI Live. There's no SAE.* or GM.* injector duty cycle pid.
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Either way, as I stated before, I believe IFR should be set accurately and not used as a tuning table. It's purpose, if I understand correctly, it to tell the PCM how the injectors react to a changing manifold vacuum (think of drinking out of a straw). The more vacuum, the easier they will flow once the window (IPW) opens up. Wasn't this table added due to the absence of a vacuum referenced fuel pressure regulator? That's the purpose it serves IMO.
The PCM should then take the other variables it knows (along with what it knows about injector performance) to calculate fuel delivery. Assuming we can determine the constants around the injector's true performance (true fuel pressure, true injector offset, true flow rate, etc.) for all of the various types of driving, we should be able to eliminate the variables and improve fueling accuracy. The problem is, we don't have that information and all we can do is guess. That's what has me so frustrated...
The PCM should then take the other variables it knows (along with what it knows about injector performance) to calculate fuel delivery. Assuming we can determine the constants around the injector's true performance (true fuel pressure, true injector offset, true flow rate, etc.) for all of the various types of driving, we should be able to eliminate the variables and improve fueling accuracy. The problem is, we don't have that information and all we can do is guess. That's what has me so frustrated...
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From: Commerce Twp, MI
Originally Posted by NicD
I know there is not a real injector duty cycle pid from the computer, that's not what I was getting at. Can you tell us all how the standard calculated IDC pid is calculated in the scanner?
IPW*RPM/1200=IDC%
Originally Posted by SSpdDmon
Either way, as I stated before, I believe IFR should be set accurately and not used as a tuning table. It's purpose, if I understand correctly, it to tell the PCM how the injectors react to a changing manifold vacuum (think of drinking out of a straw). The more vacuum, the easier they will flow once the window (IPW) opens up. Wasn't this table added due to the absence of a vacuum referenced fuel pressure regulator? That's the purpose it serves IMO.
The PCM should then take the other variables it knows (along with what it knows about injector performance) to calculate fuel delivery. Assuming we can determine the constants around the injector's true performance (true fuel pressure, true injector offset, true flow rate, etc.) for all of the various types of driving, we should be able to eliminate the variables and improve fueling accuracy. The problem is, we don't have that information and all we can do is guess. That's what has me so frustrated...
The PCM should then take the other variables it knows (along with what it knows about injector performance) to calculate fuel delivery. Assuming we can determine the constants around the injector's true performance (true fuel pressure, true injector offset, true flow rate, etc.) for all of the various types of driving, we should be able to eliminate the variables and improve fueling accuracy. The problem is, we don't have that information and all we can do is guess. That's what has me so frustrated...