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Throttle Limits Based on MAF Reading

Practical Reflash Tuning

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Discussion and questions related to the course Practical Reflash Tuning

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Short intro: I specialize in performance Nissan MR16DDT's. Tuning is done with uprev. Standalone is not possible at this time due to DI and trigger issues, and customer road cars.

I recently got ready to push two customers cars to over 500 horsepower. same build in each car. No one has ever done a turbo this large on this engine, I have built several 400 horsepower ones. I am using a BPT dominator 5.0xt-r, (yes i know its a subaru turbo, i have my reasons for using these). On a smaller turbo, the 1.5Xt-r, I have zero issues. Tuning as normal. Upgraded MAF, upgraded MAP, cars work fine. Speed density is not an option with this software (I wish it was).

Issue: With the 1.5xt-r, the throttle opens as it should ,revs as it should. The larger turbo cars will not open their throttles more than 50%. Under no load, its like they hit a wall, it goes lean, almost like its hitting a limiter, throttle sits at 50%. Under load, the throttle doesnt open past 50%, but will accelerate. Under load, I have no issue tuning at the partial throttle. Everything adjusts and changes as it should. Today I confirmed the issue is turbo size related when the second car started doing the same as the first car. I have tried stock MAF housings, Stock MAFs, 3" MAF housings with both style mafs. Both cars currently have stock MAP sensors in them.

The only thing I can think is happening is that the larger turbo is not pulling in enough air on initial throttle open, so the MAF is not seeing enough air, and thus limits throttle because of something in the ECU telling it to. But the issue with my theory is, when the car is on the dyno, making 21psi (so lots of air over the MAF) the throttle still does not open all the way.

I am stumped. Any suggestions? Other than going standalone ect. Can provide screen grabs and data logs if need be. but the data is not really telling me much.

I think you probably need to be working with UpRev on this.

Are you hitting a MAF limit? Are you finding yourself at the limit of any of the tables when this happens?

Are there any torque limiting tables, or gear based limits on throttle / airflow?

If you aren't able to see the problem from the logs, perhaps you aren't logging the correct parameters/channels. I suggest logging every channel that is used as an input to tables related to torque or throttle control.

Good Luck!

I tried to go to the UPRev website to download the manual, and that have nothing (says update coming). Not very helpful.

I found an older UpRev tuning guide that talks about a Setting, ETC On/Off. Turning this off disables the torque management aspects of the throttle control, and makes the throttle opening directly proportional to the pedal position. They caution this disables the cruise control and is actually too touchy even for race drivers. But it may be just what you need for the dyno.

Somewhere there's going to be a torque management table with estimated torque for various MAF/Throttle positions. Maybe even the Pedal table needs to request more torque to reach 100 % throttle.

i disabled the TCS and at no load it seems to have worked! I have always been told not to touch that setting, so i didnt think to try that. The guy who taught me how to tune just flat out said ignore its even there...10 years ago... lol YOU ARE A LIFE SAVER! Testing on the road and dyno tomorrow! Thank you!