[SpeedIsLife]

It wouldn't surprise me if GM's ECU programming is self learning/correcting to the point where most basic mods, including very basic tunes, will eventually be corrected back to baseline.

Remember folks, GM doesn't want you modifying these cars, and they're going to eventually force it to the point where you can't. Want more power than factory stock? Pay out the nose for a GM Performance Parts pack/intake/etc to pick up 20HP.

[TSloper]

When it comes to fueling there are two modes that matter... closed loop and open loop. Closed loop is the mode you are in when you are at part throttle. Under 4000 RPMs the ECM will calculate, in real time, g/cyl based on a number of variables. There is no longer a lookup based VE table. The ECM is also getting a measured air mass value via the MAF. The calculated and measured are blended to come up with a final g/cyl value. The injector PW is then calculated based on this final g/cyl value. The equations used to calculate the g/cyl number utilize a set of fixed coefficients. These coefficients are specific to the exact factory configuration the engine. Any change (intake manifold, headers, ported heads, cam, etc) will cause the calculated g/cyl to be wrong. It could be a little wrong or it could be a lot wrong. Small error amounts will be corrected by the S Trims and L Trims. There are limits to how much the ECM can compensate for error in the closed loop mode. A properly designed cold air intake will at a minimum ensure that on a stock setup you will not exceed the boundaries of the compensation capability. If there error is significant you have no choice but to tune and calculate a new set of coefficients that allow the ECM to properly calculate the g/cyl value. If the MAF is off considerably due to the cold air intake then you will need to recalibrate the MAF transfer function as well. Bottom line is that the ECM in this mode is just trying to maintain an AFR at stoich (14.11:1) according to the primary O2 sensors. It can apply "some" correction for error but it isn't unlimited in its ability.

In open loop mode the ECM uses the MAF exclusively above 4000 RPMs. The ECM also loses its ability to compensate for error in a granular way. When you hit the throttle and go WOT the ECM will use the last used L Trim value. If it was negative the L Trim will have zero impact on fueling at WOT. If there is a lean area you are stuck with the lean area. It won't be able to help you. If the L Trim was positive when you went WOT the ECM will add that extra fuel whether you need it or not at WOT across the RPM range up to redline. Because you are running only on MAF here it is the critical path in getting the fueling correct.

Different mods will create different scenarios but it is critical you understand what a mod has done to the entire system. If I throw on headers and my L Trims are 15% positive most of the time guess what... I am now screwing up my WOT fueling by roughly that amount. Yes the car will run and you may not feel anything wrong but it is wrong. So the increase flow may get minimized by poor fueling and non ideal timing.

The message here is that the ECM is not trying to learn out a modification. It is not trying to keep the power at stock levels. All it can do is try to compensate to keep the closed loop mode on target. That compensation can have unintended consequences when it comes to maximum power generation. This is why I harp on the data side of this so much. You can't just assume that because you bolt on a new part you are getting the benefit you think you paid for. Sound is the least credible indicator of performance. Your butt is the second least credible when you are talking 2-5% changes.

GM did a really nice job on this platform. If you can go to 93 octane fuel there is absolutely torque to be gained across the board via tuning. E85 will offer even more torque output. Tuning by far gives the best bang for the buck versus any bolt on. To maximize any bolt on it will require at least looking at the data and potential changing the ECM calibration to keep fuel and timing optimal. The ECM is NOT trying to hold you back. It just isn't designed to optimally accommodate system changes. It is designed to adapt to fuel and environmental changes (weather, altitude, etc) and keep emissions in check.

[Wheel Team 6]

Originally Posted by DiGiam

The only tuners close to me that I would trust are Jeremy formato of fasterproms or Matt at FSP. Don't need an eBay plug in performance module tearing the car up.

+1

[reeper]

Originally Posted by TSloper

When it comes to fueling there are two modes that matter... closed loop and open loop. Closed loop is the mode you are in when you are at part throttle. Under 4000 RPMs the ECM will calculate, in real time, g/cyl based on a number of variables. There is no longer a lookup based VE table. The ECM is also getting a measured air mass value via the MAF. The calculated and measured are blended to come up with a final g/cyl value. The injector PW is then calculated based on this final g/cyl value. The equations used to calculate the g/cyl number utilize a set of fixed coefficients. These coefficients are specific to the exact factory configuration the engine. Any change (intake manifold, headers, ported heads, cam, etc) will cause the calculated g/cyl to be wrong. It could be a little wrong or it could be a lot wrong. Small error amounts will be corrected by the S Trims and L Trims. There are limits to how much the ECM can compensate for error in the closed loop mode. A properly designed cold air intake will at a minimum ensure that on a stock setup you will not exceed the boundaries of the compensation capability. If there error is significant you have no choice but to tune and calculate a new set of coefficients that allow the ECM to properly calculate the g/cyl value. If the MAF is off considerably due to the cold air intake then you will need to recalibrate the MAF transfer function as well. Bottom line is that the ECM in this mode is just trying to maintain an AFR at stoich (14.11:1) according to the primary O2 sensors. It can apply "some" correction for error but it isn't unlimited in its ability.

In open loop mode the ECM uses the MAF exclusively above 4000 RPMs. The ECM also loses its ability to compensate for error in a granular way. When you hit the throttle and go WOT the ECM will use the last used L Trim value. If it was negative the L Trim will have zero impact on fueling at WOT. If there is a lean area you are stuck with the lean area. It won't be able to help you. If the L Trim was positive when you went WOT the ECM will add that extra fuel whether you need it or not at WOT across the RPM range up to redline. Because you are running only on MAF here it is the critical path in getting the fueling correct.

Different mods will create different scenarios but it is critical you understand what a mod has done to the entire system. If I throw on headers and my L Trims are 15% positive most of the time guess what... I am now screwing up my WOT fueling by roughly that amount. Yes the car will run and you may not feel anything wrong but it is wrong. So the increase flow may get minimized by poor fueling and non ideal timing.

The message here is that the ECM is not trying to learn out a modification. It is not trying to keep the power at stock levels. All it can do is try to compensate to keep the closed loop mode on target. That compensation can have unintended consequences when it comes to maximum power generation. This is why I harp on the data side of this so much. You can't just assume that because you bolt on a new part you are getting the benefit you think you paid for. Sound is the least credible indicator of performance. Your butt is the second least credible when you are talking 2-5% changes.

GM did a really nice job on this platform. If you can go to 93 octane fuel there is absolutely torque to be gained across the board via tuning. E85 will offer even more torque output. Tuning by far gives the best bang for the buck versus any bolt on. To maximize any bolt on it will require at least looking at the data and potential changing the ECM calibration to keep fuel and timing optimal. The ECM is NOT trying to hold you back. It just isn't designed to optimally accommodate system changes. It is designed to adapt to fuel and environmental changes (weather, altitude, etc) and keep emissions in check.

Best write up I've seen yet on bolt-onsite. Thank you.

[Hyper1SS]

Originally Posted by TSloper

When it comes to fueling there are two modes that matter... closed loop and open loop. Closed loop is the mode you are in when you are at part throttle. Under 4000 RPMs the ECM will calculate, in real time, g/cyl based on a number of variables. There is no longer a lookup based VE table. The ECM is also getting a measured air mass value via the MAF. The calculated and measured are blended to come up with a final g/cyl value. The injector PW is then calculated based on this final g/cyl value. The equations used to calculate the g/cyl number utilize a set of fixed coefficients. These coefficients are specific to the exact factory configuration the engine. Any change (intake manifold, headers, ported heads, cam, etc) will cause the calculated g/cyl to be wrong. It could be a little wrong or it could be a lot wrong. Small error amounts will be corrected by the S Trims and L Trims. There are limits to how much the ECM can compensate for error in the closed loop mode. A properly designed cold air intake will at a minimum ensure that on a stock setup you will not exceed the boundaries of the compensation capability. If there error is significant you have no choice but to tune and calculate a new set of coefficients that allow the ECM to properly calculate the g/cyl value. If the MAF is off considerably due to the cold air intake then you will need to recalibrate the MAF transfer function as well. Bottom line is that the ECM in this mode is just trying to maintain an AFR at stoich (14.11:1) according to the primary O2 sensors. It can apply "some" correction for error but it isn't unlimited in its ability.

In open loop mode the ECM uses the MAF exclusively above 4000 RPMs. The ECM also loses its ability to compensate for error in a granular way. When you hit the throttle and go WOT the ECM will use the last used L Trim value. If it was negative the L Trim will have zero impact on fueling at WOT. If there is a lean area you are stuck with the lean area. It won't be able to help you. If the L Trim was positive when you went WOT the ECM will add that extra fuel whether you need it or not at WOT across the RPM range up to redline. Because you are running only on MAF here it is the critical path in getting the fueling correct.

Different mods will create different scenarios but it is critical you understand what a mod has done to the entire system. If I throw on headers and my L Trims are 15% positive most of the time guess what... I am now screwing up my WOT fueling by roughly that amount. Yes the car will run and you may not feel anything wrong but it is wrong. So the increase flow may get minimized by poor fueling and non ideal timing.

The message here is that the ECM is not trying to learn out a modification. It is not trying to keep the power at stock levels. All it can do is try to compensate to keep the closed loop mode on target. That compensation can have unintended consequences when it comes to maximum power generation. This is why I harp on the data side of this so much. You can't just assume that because you bolt on a new part you are getting the benefit you think you paid for. Sound is the least credible indicator of performance. Your butt is the second least credible when you are talking 2-5% changes.

GM did a really nice job on this platform. If you can go to 93 octane fuel there is absolutely torque to be gained across the board via tuning. E85 will offer even more torque output. Tuning by far gives the best bang for the buck versus any bolt on. To maximize any bolt on it will require at least looking at the data and potential changing the ECM calibration to keep fuel and timing optimal. The ECM is NOT trying to hold you back. It just isn't designed to optimally accommodate system changes. It is designed to adapt to fuel and environmental changes (weather, altitude, etc) and keep emissions in check.

Very well put!! Can't wait to see you and Lethals findings and numbers on the Roto-Fab intake. I think it is a well built and quality intake. Glad they decided to go to the bigger box and filter. Will be looking out for your findings. Hope all is well there with the weather recently.

[BradfordCamaro]

Originally Posted by TSloper

When it comes to fueling there are two modes that matter... closed loop and open loop. Closed loop is the mode you are in when you are at part throttle. Under 4000 RPMs the ECM will calculate, in real time, g/cyl based on a number of variables. There is no longer a lookup based VE table. The ECM is also getting a measured air mass value via the MAF. The calculated and measured are blended to come up with a final g/cyl value. The injector PW is then calculated based on this final g/cyl value. The equations used to calculate the g/cyl number utilize a set of fixed coefficients. These coefficients are specific to the exact factory configuration the engine. Any change (intake manifold, headers, ported heads, cam, etc) will cause the calculated g/cyl to be wrong. It could be a little wrong or it could be a lot wrong. Small error amounts will be corrected by the S Trims and L Trims. There are limits to how much the ECM can compensate for error in the closed loop mode. A properly designed cold air intake will at a minimum ensure that on a stock setup you will not exceed the boundaries of the compensation capability. If there error is significant you have no choice but to tune and calculate a new set of coefficients that allow the ECM to properly calculate the g/cyl value. If the MAF is off considerably due to the cold air intake then you will need to recalibrate the MAF transfer function as well. Bottom line is that the ECM in this mode is just trying to maintain an AFR at stoich (14.11:1) according to the primary O2 sensors. It can apply "some" correction for error but it isn't unlimited in its ability.

In open loop mode the ECM uses the MAF exclusively above 4000 RPMs. The ECM also loses its ability to compensate for error in a granular way. When you hit the throttle and go WOT the ECM will use the last used L Trim value. If it was negative the L Trim will have zero impact on fueling at WOT. If there is a lean area you are stuck with the lean area. It won't be able to help you. If the L Trim was positive when you went WOT the ECM will add that extra fuel whether you need it or not at WOT across the RPM range up to redline. Because you are running only on MAF here it is the critical path in getting the fueling correct.

Different mods will create different scenarios but it is critical you understand what a mod has done to the entire system. If I throw on headers and my L Trims are 15% positive most of the time guess what... I am now screwing up my WOT fueling by roughly that amount. Yes the car will run and you may not feel anything wrong but it is wrong. So the increase flow may get minimized by poor fueling and non ideal timing.

The message here is that the ECM is not trying to learn out a modification. It is not trying to keep the power at stock levels. All it can do is try to compensate to keep the closed loop mode on target. That compensation can have unintended consequences when it comes to maximum power generation. This is why I harp on the data side of this so much. You can't just assume that because you bolt on a new part you are getting the benefit you think you paid for. Sound is the least credible indicator of performance. Your butt is the second least credible when you are talking 2-5% changes.

GM did a really nice job on this platform. If you can go to 93 octane fuel there is absolutely torque to be gained across the board via tuning. E85 will offer even more torque output. Tuning by far gives the best bang for the buck versus any bolt on. To maximize any bolt on it will require at least looking at the data and potential changing the ECM calibration to keep fuel and timing optimal. The ECM is NOT trying to hold you back. It just isn't designed to optimally accommodate system changes. It is designed to adapt to fuel and environmental changes (weather, altitude, etc) and keep emissions in check.

Lets quote the longest post ever.....

But seriously.

This what I was thinking and you saved me alot of spell checks. Thanks.

[vtirocz]

Originally Posted by TSloper

When it comes to fueling there are two modes that matter... closed loop and open loop. Closed loop is the mode you are in when you are at part throttle. Under 4000 RPMs the ECM will calculate, in real time, g/cyl based on a number of variables. There is no longer a lookup based VE table. The ECM is also getting a measured air mass value via the MAF. The calculated and measured are blended to come up with a final g/cyl value. The injector PW is then calculated based on this final g/cyl value. The equations used to calculate the g/cyl number utilize a set of fixed coefficients. These coefficients are specific to the exact factory configuration the engine. Any change (intake manifold, headers, ported heads, cam, etc) will cause the calculated g/cyl to be wrong. It could be a little wrong or it could be a lot wrong. Small error amounts will be corrected by the S Trims and L Trims. There are limits to how much the ECM can compensate for error in the closed loop mode. A properly designed cold air intake will at a minimum ensure that on a stock setup you will not exceed the boundaries of the compensation capability. If there error is significant you have no choice but to tune and calculate a new set of coefficients that allow the ECM to properly calculate the g/cyl value. If the MAF is off considerably due to the cold air intake then you will need to recalibrate the MAF transfer function as well. Bottom line is that the ECM in this mode is just trying to maintain an AFR at stoich (14.11:1) according to the primary O2 sensors. It can apply "some" correction for error but it isn't unlimited in its ability.

In open loop mode the ECM uses the MAF exclusively above 4000 RPMs. The ECM also loses its ability to compensate for error in a granular way. When you hit the throttle and go WOT the ECM will use the last used L Trim value. If it was negative the L Trim will have zero impact on fueling at WOT. If there is a lean area you are stuck with the lean area. It won't be able to help you. If the L Trim was positive when you went WOT the ECM will add that extra fuel whether you need it or not at WOT across the RPM range up to redline. Because you are running only on MAF here it is the critical path in getting the fueling correct.

Different mods will create different scenarios but it is critical you understand what a mod has done to the entire system. If I throw on headers and my L Trims are 15% positive most of the time guess what... I am now screwing up my WOT fueling by roughly that amount. Yes the car will run and you may not feel anything wrong but it is wrong. So the increase flow may get minimized by poor fueling and non ideal timing.

The message here is that the ECM is not trying to learn out a modification. It is not trying to keep the power at stock levels. All it can do is try to compensate to keep the closed loop mode on target. That compensation can have unintended consequences when it comes to maximum power generation. This is why I harp on the data side of this so much. You can't just assume that because you bolt on a new part you are getting the benefit you think you paid for. Sound is the least credible indicator of performance. Your butt is the second least credible when you are talking 2-5% changes.

GM did a really nice job on this platform. If you can go to 93 octane fuel there is absolutely torque to be gained across the board via tuning. E85 will offer even more torque output. Tuning by far gives the best bang for the buck versus any bolt on. To maximize any bolt on it will require at least looking at the data and potential changing the ECM calibration to keep fuel and timing optimal. The ECM is NOT trying to hold you back. It just isn't designed to optimally accommodate system changes. It is designed to adapt to fuel and environmental changes (weather, altitude, etc) and keep emissions in check.

Thanks for that explanation. Does GM use a torque command based on pedal position / engine speed? I was thinking the ECM calculated torque accuracy could be off (depending on the bolt-on and MAF accuracy), which could impact the real torque curve (and performance beneath it). IF there is a torque command, then you're not going to get higher than that without a tune, unless the torque accuracy is off from the hardware modification.

[TSloper]

The driver demand table is based on pedal position and vehicle speed. It will look up the desired axle torque (engine TQ x transmission ratio x rear gear ratio) based on those two inputs and try to achieve that. Assuming no other systems (ie. TQ management, etc) override that request the ECM will adjust the throttle bladed to the minimum amount of opening to achieve that torque. The ECM can't measure actual torque so based on all of the modeling and coefficients GM came up with it is calculating what it believes to be the torque output. If a modification such as a supercharger grossly exceeds the demanded TQ the ECM will close the throttle blade to try and keep you at or below the demanded value. This can be corrected for. Bolts aren't going to get you any where near this situation so that isn't something anyone needs to worry about.

It's really simple... bolt ons have the potential to add additional power but on this platform they really did optimize the stock system within the boundaries of having to maintain emissions and adapt to any given weather/altitude condition. To maximize bolt on gains tuning is required.

[vtirocz]

Originally Posted by TSloper

The driver demand table is based on pedal position and vehicle speed. It will look up the desired axle torque (engine TQ x transmission ratio x rear gear ratio) based on those two inputs and try to achieve that. Assuming no other systems (ie. TQ management, etc) override that request the ECM will adjust the throttle bladed to the minimum amount of opening to achieve that torque. The ECM can't measure actual torque so based on all of the modeling and coefficients GM came up with it is calculating what it believes to be the torque output. If a modification such as a supercharger grossly exceeds the demanded TQ the ECM will close the throttle blade to try and keep you at or below the demanded value. This can be corrected for. Bolts aren't going to get you any where near this situation so that isn't something anyone needs to worry about.

It's really simple... bolt ons have the potential to add additional power but on this platform they really did optimize the stock system within the boundaries of having to maintain emissions and adapt to any given weather/altitude condition. To maximize bolt on gains tuning is required.

Thanks. So at 100% pedal position, won't the ECM still hold things to the stock torque curve (assuming the torque model is still accurate with the bolt-on hardware)?

[TSloper]

Originally Posted by vtirocz

Thanks. So at 100% pedal position, won't the ECM still hold things to the stock torque curve (assuming the torque model is still accurate with the bolt-on hardware)?

There is enough margin that bolt ons won't see that behavior.

[NinjaBum]

Originally Posted by DiGiam

The only tuners close to me that I would trust are Jeremy formato of fasterproms or Matt at FSP. Don't need an eBay plug in performance module tearing the car up.

Ugh...