MODS with GM1 Tune
02-20-2016, 02:18 AM
#51
Senior Member
FOR GMTU(or GMS1 as you guys call it)
The tune was designed to deliver torque and HP at a certain value which means the ECM will do everything it's capable of doing to limit your TQ and HP output at xxxxrpm. Bolt ons for the purpose of adding power is a WASTE with GMTU if you are looking for dyno # improvements.
Any and all modifications in the intake tract that changes the way the air moves past the MAF can and will skew trims. The ECM/tune is adaptive and will compensate to a degree iirc.
The tune was designed to deliver torque and HP at a certain value which means the ECM will do everything it's capable of doing to limit your TQ and HP output at xxxxrpm. Bolt ons for the purpose of adding power is a WASTE with GMTU if you are looking for dyno # improvements.
Any and all modifications in the intake tract that changes the way the air moves past the MAF can and will skew trims. The ECM/tune is adaptive and will compensate to a degree iirc.
02-20-2016, 03:42 AM
#53
Senior Member
02-20-2016, 10:04 AM
#54
Senior Member
More importantly, LNFwagonSS pointed out that GMS1 does not truly disable the Learn Down feature of the car, it just has it raised to a higher than stock level.
Whatever tune you run, this car is going to attempt to hit the programmed power output. It's not as simple as some other torque based ECU where it will flat out attempt to hit a set amount of LbFt of torque. The LNF is a tiny bit more complicated in the sense that it calculates demanded torque as a function of desired torque as a percentage of requested Airload.
You will notice when you break the tires loose boost will drop, because the car is calculating excessive torque output and will alter the desired Airload to attempt to bring calculated torque back down to the same level as requested torque.
likewise, if you bog the car at full throttle in a high gear, you may experience overboost. The car will be sensing that measured wheel torque is lower than demamded, and will increase Airload (up to preset pressure limits) to attempt to hit a target torque output.
This is essentially what "Learn Down" is. If you alter other things in your tune that increase power output, such as bumping up timing advance, the car will theoretically hit the requested torque output without the need for as much boost. You would then see a drop in boost (as long as you were already hitting your demanded torque without exceeding the Airload limits).
Now, if you go and throw an intake on the car that alters the STFT and LTFT values versus MAF frequency (and all intakes will) then you will be also altering the calculated amount of airflow. This can translate into undesired changes to the requested amount of airflow relative to engine load and rpm, and cause your car to run differently than intended. Either way, it will still limit itself to producing only the desired torque output.
Whatever tune you run, this car is going to attempt to hit the programmed power output. It's not as simple as some other torque based ECU where it will flat out attempt to hit a set amount of LbFt of torque. The LNF is a tiny bit more complicated in the sense that it calculates demanded torque as a function of desired torque as a percentage of requested Airload.
You will notice when you break the tires loose boost will drop, because the car is calculating excessive torque output and will alter the desired Airload to attempt to bring calculated torque back down to the same level as requested torque.
likewise, if you bog the car at full throttle in a high gear, you may experience overboost. The car will be sensing that measured wheel torque is lower than demamded, and will increase Airload (up to preset pressure limits) to attempt to hit a target torque output.
This is essentially what "Learn Down" is. If you alter other things in your tune that increase power output, such as bumping up timing advance, the car will theoretically hit the requested torque output without the need for as much boost. You would then see a drop in boost (as long as you were already hitting your demanded torque without exceeding the Airload limits).
Now, if you go and throw an intake on the car that alters the STFT and LTFT values versus MAF frequency (and all intakes will) then you will be also altering the calculated amount of airflow. This can translate into undesired changes to the requested amount of airflow relative to engine load and rpm, and cause your car to run differently than intended. Either way, it will still limit itself to producing only the desired torque output.
02-20-2016, 10:16 AM
#55
Originally Posted by Psykostevo
And gains are very much in the single digit level. Gutting the stocker sure does save money ;-)
I usually suggest to people that if they want 3-5 more horsepower and don't mind paying a few hundred bucks for it, and want to take off their down pipe, then go for it. But otherwise keep the money in your pocket. These stock cats aren't the bane of existence, and $100 per horsepower is too steep for many people.
Worst is when they spend $500 - $1000 on exhaust and expect to be making more power because of it. Or a couple to a few hundred on intake and either gain nothing or lose power from it.
I usually suggest to people that if they want 3-5 more horsepower and don't mind paying a few hundred bucks for it, and want to take off their down pipe, then go for it. But otherwise keep the money in your pocket. These stock cats aren't the bane of existence, and $100 per horsepower is too steep for many people.
Worst is when they spend $500 - $1000 on exhaust and expect to be making more power because of it. Or a couple to a few hundred on intake and either gain nothing or lose power from it.
02-20-2016, 01:00 PM
#56
Senior Member
Keep in mind, while changing the intake will skew trims, its possible that it will bring them closer to zero depending on the intake change, current MAF calibration, and a few other variables. Some LNF HHR owners have found that the K&n intake kit improved LTFT. Obviously the HHR has a completely different intake setup so this will not apply to cobalts. The k&n intake tube for hhr is not much different/bigger than stock. It's just a smoother flow.
02-22-2016, 11:17 AM
#58
MAF measures air in the intake.
Charge pipe and intercooler then alters airflow into engine. Which results in variations from what the MAF just calculated. Your car will begin adjusting fuel trims to try and match.
Basically any time you change the airflow in and out, your car has to adjust. Thereby skewing your fueling. Now some do that positively and some negatively. But yes they are skewed.
Charge pipe and intercooler then alters airflow into engine. Which results in variations from what the MAF just calculated. Your car will begin adjusting fuel trims to try and match.
Basically any time you change the airflow in and out, your car has to adjust. Thereby skewing your fueling. Now some do that positively and some negatively. But yes they are skewed.
02-22-2016, 11:35 AM
#59
Senior Member
You do have to remember that when calibrating the MAF, you are adjusting for Fuel Trims. The Fuel Trims come as a result of data measured at the Oxygen sensors, which are obviously much further downstream than the MAF sensor. So we are calibrating at inlet for the resulting combustion measured at the outlet.
Having cooler, or faster airflow can and will alter the burn rate of the fuel, and therefor have a potential to manipulate the fuel trims.
Having cooler, or faster airflow can and will alter the burn rate of the fuel, and therefor have a potential to manipulate the fuel trims.
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