2013 Zl1 1st gear wot pull.

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Hi guys I have a 2013 Camaro ZL1 with a 4L80 conversion, I'm using a DSX conversion harness and t42 controller, when I launch the car on 1/4 mile pass it gets to about 6 to 7 mph and slows down to 4 mph and then it takes off from there. I have all the torque management turned off and it still does it did I miss a setting? Also at the top of the 1st gear pull the rpms start to come down is this just the car catching up to the converter or is there something else going on. The car makes around 840 whp best pass so far is 9.84. The trans has a Jakes stage 5 kit with no trans brake, Circle D 3800 triple disc converter. Here's copy of a typical 1/4 mile pass and a copy of my tune. Thanks for your help.

[10_SS]

Some strangeness could be wheelspin I guess. Can you log the Undriven wheel speed (Front)? That will tell you how much spin you have. The 5mph thing seems fishy since it comes down to 4.3mph and doesn't change at all for a few data points.. then jumps back up but it happens internally in the trans as well, but not with engine RPM. The Undriven wheel speed is very accurate since it uses the large high res ABS ring, you could have some constant wheelspin affecting the rate of change to RPM and such, which shows up in strange ways, it could be regaining traction at 36mph where the rate of change seems to lessen quite a bit. I had this "problem" on a dyno with a very experienced operator once.. RPM just kinda hung flat for awhile, sounded like a motor problem was was just wheelspin, tires getting hot and regaining traction as it slipped.

The 5mph thing, I dont know. Could also be wheelspin since RPM appears constant through it but it's actually not, its hanging a bit, then half way through it starts to pick up speed. All trans shaft speeds show a decrease in rate of change as well.

Check the undriven wheel speed. It may just be wheelspin.

[Xjas]

Log driven and undriven wheel speed, SAE vehicle speed does some strange things, like it is a filtered value or averaged over time or something, if you log the 3 together you'll see that when the driven and undriven don't match the SAE vehicle speed goes all out of whack.

[smokeshow]

That is a shit ton of converter flash. Circle D converters definitely like to couple at very high RPM. I don't think I'd worry about it, unless something actually feels wrong. Friend of mine who has me tune his turbo setup regularly has a pretty loose Circle D as well, it acts similar to that. Jumps up to about 200rpm shy of the shift point real quick and just hangs there until the converter catches up. But it runs hard, so we leave it be.

[1bad68ls]

Considering that you are running an automatic, I don't think it is wheelspin, otherwise you would see it on the VSS trace.

I have 2 possibilities:
1) During launch (especially up against a line lock in the staging lane), I occasionally ran into noise issues on the VSS signal (with a different car - not a ZL1), which was due to the speed sensor was on the edge of the speed sensor gear tooth... and occasionally gave me a false MPH reading (at the start only). GM "filters" the MPH signal... and it is possible the first 1/4 second of your signal is not accurate.
2) Another possibility is... The output shaft torque appear to be reduced for 2 tenths of a second, which could also be your clutch pack slipping at launch... possibly due to inconsistent line pressure at launch???

I would compare it against the undriven wheel speed and possibly log your trans line pressure if you are concerned about it.

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Thank you guys for taking time to look at this, I'm going to start to log driven and undriven wheel speed and compare them with rpm, mph and output shaft. This winter I'm going to add a pressure sensor to the transmission so I can keep a eye on that also, all this may be nothing the car seems to pull hard all the way thru the pass but I saw it on my logs and thought I would ask the guys that know more than I do, is there anything else that I should be logging that would help?

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What pressure sensor for the 4L80 are you guys using with HP tuners.