Wonky Rev Match on Cammed C7 Z06 (M7 Trans)

[M3T1]

Did heads & cam on my car recently. My tuner got the tune pretty good on the dyno. Drivability is good. Startup & idle are great.

The only issue I am having is that my rev match is spazzing out on downshifts. On upshifts, it appears to be fine. On downshifts, the throttle blips up, falls, blips back up, falls, etc. over and over. I'm trying to figure out what we did wrong/are missing. We updated the torque model, and our predicted torque matches our delivered engine torque really well throughout the RPM range (this was off upon installing the cam prior to tuning obviously). Throttle stays 100% open through a dyno pull, and torque management isn't pulling timing on us. So, we thought we set it up pretty well, but evidently, we missed something.

I attached the tune file if anyone can discern something from it. Any help would be greatly appreciated.

2-15-21 JT Tune.hpt

[SultanHassanMasTuning]

can you post a log of the issue

[M3T1]

can you post a log of the issue

I did a bunch of downshifts in this log. The first series starts at 15:34:51 and you can see me do 2 in a row (4-3 shift and then 3-2 shift).

I do see that the delivered engine torque spikes right as the rev match kicks in, it pulls timing, then adds timing back in. Could be a torque issue, but I'm not sure where because it only happens with rev match.

downshift rev match flutter.hpl

[M3T1]

Also, not sure if it's related, but my hill assist is being weird. It's holding the car too long, so it's like I have to power through the brakes for a second to start moving. When we put the cam in, we did install a monster triple disc clutch. That's the only other thing I noticed that's weird.

[TriPinTaZ]

This is a symptom of an issue in Driver Demand and Virtual Torque.

[M3T1]

Hmmmm maybe we overshot in virtual torque or something.

[M3T1]

This is a symptom of an issue in Driver Demand and Virtual Torque.

I messed with it more today, and none of my changes made any difference. I did notice in a previous log (from before the cam install) that it did a more minor version of that flutter from the factory. I'm really not sure what to do at this point.

[TriPinTaZ]

Your log doesn't log any torque parameters. I assume your cam is locked at zero based on your virtual torque changes but you haven't finished the rest of zeroing out the rest of the tables. Your Virtual Torque table is heavily changed unnecessarily. Your Driver Demand is also increased way too far, probably because you increased the VT so much. your Peak Torque tables needs to be shaped a little better to follow the new power output of the mods rather than just adding 200 everywhere.

Why were things increased so much? Were you having throttle closing issues? You've increased your MAF already which will directly increase torque output so jacking up the Virtual Torque Tables isn't helping. What happens when you put the Torque tables and Driver Demand back to stock? This is where you should start and adjust to address and throttle closing. I have found the best drive-ability is when the Torque Model stays closer to stock and then you adjust the torque stuff based on need.

[M3T1]

Your log doesn't log any torque parameters. I assume your cam is locked at zero based on your virtual torque changes but you haven't finished the rest of zeroing out the rest of the tables. Your Virtual Torque table is heavily changed unnecessarily. Your Driver Demand is also increased way too far, probably because you increased the VT so much. your Peak Torque tables needs to be shaped a little better to follow the new power output of the mods rather than just adding 200 everywhere.

Why were things increased so much? Were you having throttle closing issues? You've increased your MAF already which will directly increase torque output so jacking up the Virtual Torque Tables isn't helping. What happens when you put the Torque tables and Driver Demand back to stock? This is where you should start and adjust to address and throttle closing. I have found the best drive-ability is when the Torque Model stays closer to stock and then you adjust the torque stuff based on need.

The log should have commanded torque, predicted torque, and delivered torque in it. The cam is locked at zero and we set variable camshafts to "none". What tables would I have to zero? The only cam angle that will ever be seen is 0 degrees, so it shouldn't matter what is in the 10, 20, and 30 degree tables.

Driver demand was increased up top because we were having throttle closure during pulls. We originally hadn't messed with that. We messed with the torque model thinking that was the problem, but then we raised driver demand and the throttle stopped closing. I did try with the virtual torque tables back to stock, and I have the same issue. The behavior is exactly the same. I'm going to leave the virtual torque back at stock for now though. You're right that we went way too crazy there thinking that was the cause of the throttle closure haha oops!

I was thinking peak torque was a torque limitation parameter like the rpm vs. gear torque limiting. I set that back to stock. Will see if that makes a difference. I had already reverted my torque model back to stock after I posted the tune here. Hopefully it was just the peak torque being off. I was thinking "peak torque" was an overall limiter, not the expected peak torque.

[M3T1]

I just tried it with the peak tables set back to stock and rev match is still wonky. Doesn't seem to be the cause.

[TriPinTaZ]

What throttle body are you using?

[HeavyChevy305]

Full list of mods please...

[M3T1]

Ended up figuring it out. VE tables were off. I guess even in MAF-only mode, the rev match uses VE. Since it was off, it was all confused. We did a VE tune, and it's all good now.

[Ben Charles]

VE is used even with it set at 400 RPMs.. we discovered this many years ago!!

[M3T1]

VE is used even with it set at 400 RPMs.. we discovered this many years ago!!

yeah we had it set at 500 RPM haha. I thought it was unused but apparently it still mattered. Car drives great now