2.0T Turbo Lag and Torque Management
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  1. #1
    Ragtop 99's Avatar
    Ragtop 99 is offline Cadillac Owners Enthusiast
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    2.0T Turbo Lag and Torque Management

    There has been some discussion of turbo lag of the 2.0T and how it compares to the V6. Attached below is 1 second of data logged on my car where I floor it in 2nd gear starting at roughly 3100 rpm. . This is not all the data I log, but highlights some fields that show how the ATS regulates power.

    2nd gear punch.JPG

    Here is a brief overview of some the fields that donít show up on your dashboard.

    Commanded ETC TPS: Commanded Electronic Throttle Control Throttle Position Sensor. This is reading the position of the gas pedal. There is no mechanical cable connecting the gas pedal to the throttle, so this tells the engine computer what the driver wants to do.

    Throttle Position:
    This sensor reads the actual position of the throttle blade. 84% is WOT with this sensor measurement. Why 84% max on this measurement, I donít know. There is another place I could read it, but I havenít changed my logging configuration. In some cars the throttle blade position is limited to reduce power, but that is not the case here.

    You can see there is a tiny bit of lag in opening the throttle after it is commanded to WOT. Some of this lag may be due to the frame rate being logged, but still not instantaneous like old school cars. Logging fewer parameters can increase the frame rate.

    Manifold Absolute Pressure: This is the pressure at the intake manifold. As the throttle opens, this number goes up. If a normally aspirated motor were at sea level and had no intake restrictions, it would read 100 kPa at WOT. To go above 100 requires a turbo or supercharger to force the air in.

    Desired Boost: This is calculated by the computer by comparing the power the car is making to power its wants to make. A table in the ECM limits the car to 250 kPa,. However, the stock car will never achieve 250 kPa because of the torque management tables and other limitations. My current tune removes the engine torque limits, but you can see at frame 84 the computer is starting to cut its target boost because Iím approaching other limiting restrictions on power.

    Boost Solenoid Control: This is the duty cycle that opens and closes the waste gate. At 100% all of the exhaust energy is going to turn the turbo. The stock tune limits this to 95%. As the actual kPa climbs, the duty cycle is reduced. Another ECM table takes over and will limit the duty cycle by rpm and pressure ratio. This is another way the car limits torque. It effectively prevents the turbo from making its maximum boost.

    At cruise, much less boost is used. At frame 52, the car is using a 35% duty cycle. I bumped the cruise duty cycle slightly above stock to improve part throttle response. It probably makes the car a tiny bit less fuel efficient.

    Cylinder Airmass: This is the ECMís calculation of how much is entering the cylinder each cycle. It is not a measure of a total airflow. The higher the number, the more air in the cylinder and the more fuel that can be burned in that power stroke. A low number is desirable for good MPG, and high number makes more torque. There is a table that sets the maximum g/cyl that is allowed. By limiting the air density in the cylinder, the ECM limits the power the car makes.

    Delivered torque: This is what the engine calculates it is making for power. It is compared to 3 tables that set engine torque limits. Other than brief torque spikes, the engine will limit power to hit the advertised HP and TQ values. The stock setting at 6500 rpm is 207 ft-lbs. This explains why the car feels like a turd before it upshifts.

    Turbo lag:
    So why does the turbo not feel as crisp as the V6? Look at the time at frame 56. This is when I mash the gas pedal. Look at frame 61. You can see the boost after .1 second is still pretty low as the kPa is just 105. Without the turbo, the kPa would be around 95, so not much of gain when the goal is to get to 200 kPa. The full rated torque for the stock motor is not achieved until frame 82. Thatís a half second and my car gets to stock power slightly quicker because Iíve raised the wastegate duty cycle tables.

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  3. #2
    Hot Rod Joe is offline Cadillac Owners Member
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    Re: 2.0T Turbo Lag and Torque Management

    Excellent insight into what is going on with the ECM. I love how the computer gives us only the allowed power! Does the traction control modify the map as well?

    I noticed you are getting more delivered torque than advertised. Care to comment?

  4. #3
    Ragtop 99's Avatar
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    Re: 2.0T Turbo Lag and Torque Management

    Hot Rod Joe:
    For more than the past month, I've been working on tuning the car using HP Tuners software. I have a downpipe, intake, and catch can to go on the car, hopefully in the next two weeks. The parameters above are some of the important ones in determining whether changes in the tune are working. If I make a change and delivered TQ doesn't go up, then it's back to the drawing board to figure out why.

  5. #4
    oachalon is offline Cadillac Owners Member
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    Re: 2.0T Turbo Lag and Torque Management

    I would be interested to see torque management in the 3.6 as well, cause i can feel that its there.

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    Hot Rod Joe is offline Cadillac Owners Member
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    Re: 2.0T Turbo Lag and Torque Management

    Torque management or torque truncation is not new. Ten years ago, my SRT Neon was built with this type of programming in the ECM. Bigger turbos didn't help unless you re-programmed the ECM for a '3-bar map'. Boost was reduced for all sorts of things when the ECM felt your didn't need it. Most noticible when the engine is cold and more so in 1st gear.

    Even my 1995 Supercoupe has torque reduction programmed into the engine computer. At low speed, the torque is truncated to prevent the chassis from twisting itself into a prezel. I have a programmable tuner for the Ford but never messed with it.

    My 2003 Dodge Ram PU has the torque truncation programmed in at low speed. A simple wire cut could fix that for only one model year. After that, Dodge got wise and made tinkering more difficult.

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    Ragtop 99's Avatar
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    Re: 2.0T Turbo Lag and Torque Management

    I've had LS1 and LS3 V8s and they are much more straight forward, but they weren't factory boosted cars. The nice thing about the ATS is how much power from a tune you can get. Percentage wise, it is much more than I could get from the V8s.

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    Michael167 is offline Cadillac Owners Member
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    Re: 2.0T Turbo Lag and Torque Management

    Ok, so I figure I should start here. I have an intake and downpipe on my 2013 ats and in a recent tune I spiked 335 ft-lb with 26 psi but in quite literally the next frame my throttle slammed shut to about 40 percent and killed the party. Has this happened to anyone else tuning the ats? A friend of mine is tuning his Buick verano t and running into the same problem. We share the same ECU and are a bit stuck. Any help, hints, nudges, or back hands in the right direction would be greatly appreciated (can't stress the GREATLY enough) lol

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    Ragtop 99's Avatar
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    Re: 2.0T Turbo Lag and Torque Management

    I haven't had this happen...yet. Did the torque spike coincide with wheel spin? Are you actually commanding that much boost or did the boost get away from the controller?
    Wild guesses...Under Fuel/Cutoff tab on the left side are rpm error and predicted torque. I wonder if the torque spike greatly exceeded predicted and was shutdown. I haven't mucked with these tables so it is just a guess.

    If you find out, please come back and update.

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    Michael167 is offline Cadillac Owners Member
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    Re: 2.0T Turbo Lag and Torque Management

    Ragtop, when the torque spiked we were well on our way at 42 mph and had no wheel spin. We've ruled out fuel cutoff. My friend and I believed it to be his TCM that was sending a single to shut the throttle to protect itself but now my ATS does it as well and our TCMs are different while we share the same E39a. At 4867 rpm I hit 335 peak torque, my input was still at 100% but the throttle closed to 49% at that same moment desired boost dropped to 30 and actual overtook it at almost 37 (15 and 22 after accounting for baro) Desired seems to be the one working against us right?

    ----------

    My buddy's post on a tuning forum

    Well, now the ATS I am tuning is doing this as well since I have gained a lot of power with it. Now I know for a fact that those who have successfully tuned the ATS have encountered this issue and are keeping silent. This is not a turbo A/R combination or tuning secret. Desired boost fluctuates and is too low causing any respectable amount of boost to overshoot the target and immediately shut the throttle. Somebody please help. I need to figure this out. I was humiliated at PBIR running a 14.3 @ 96 mph. I JUST need the throttle open 84% at 24 psi and I will figure out all the rest. Please, if you know how to raise Desired Boost - help. I have maxed out every limiter and tried every table in engine and tranny. Even when the settings that would obviously raise Desired Boost and do are adjusted, it still drops like a rock.It fluctuates and only wants about 15 psi or less when the car is desperate for 25. Is it in the P.I.D controller? Is it in the Map / Baro ratio or Delta pressure change? I have tried and small moves but after literally 200 re-flashed nothing (except for low boost that makes no power) keeps the throttle open on either of these cars. There is no knock and I have maxed out the S/C airflow table even. The trans. torque settings are maxed out in the ATS's T43. wtf??

  11. #10
    Chrispy's Avatar
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    Re: 2.0T Turbo Lag and Torque Management

    I believe GM dialled the 2.0 back to keep it slower than the 3.6. With a very safe tune these 2.0's will crush the 3.6 in area under the curve. Hopefully you guys can get this all figured out

  12. #11
    Michael167 is offline Cadillac Owners Member
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    Re: 2.0T Turbo Lag and Torque Management

    I won't be stopping until we do lol thanks Chrispy

  13. #12
    Ragtop 99's Avatar
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    Re: 2.0T Turbo Lag and Torque Management

    Quote Originally Posted by Michael167 View Post
    [/COLOR]My buddy's post on a tuning forum...Desired boost fluctuates and is too low causing any respectable amount of boost to overshoot the target and immediately shut the throttle. Somebody please help. I need to figure this out. I was humiliated at PBIR running a 14.3 @ 96 mph. I JUST need the throttle open 84% at 24 psi and I will figure out all the rest. Please, if you know how to raise Desired Boost - help. I have maxed out every limiter and tried every table in engine and tranny. Even when the settings that would obviously raise Desired Boost and do are adjusted, it still drops like a rock.It fluctuates and only wants about 15 psi or less when the car is desperate for 25. Is it in the P.I.D controller? Is it in the Map / Baro ratio or Delta pressure change? I have tried and small moves but after literally 200 re-flashed nothing (except for low boost that makes no power) keeps the throttle open on either of these cars. There is no knock and I have maxed out the S/C airflow table even. The trans. torque settings are maxed out in the ATS's T43. wtf??
    I have found Knock Airmass seems to correlate with desired boost. The Knock airmass number also correlates pretty closely to the Cylinder Airmass achieved (g/cyl).

  14. #13
    Michael167 is offline Cadillac Owners Member
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    Re: 2.0T Turbo Lag and Torque Management

    Looking into it now Ragtop thanks

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    Michael167 is offline Cadillac Owners Member
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    Re: 2.0T Turbo Lag and Torque Management

    That table is maxed and she still behaves the same way, need to figure this out

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    Ragtop 99's Avatar
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    Re: 2.0T Turbo Lag and Torque Management

    deleted. moved post to new thread.

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