[angryBits]

I noticed the car has a tendency to bog down when giving it 80% throttle in 4th gear around 4k rpm. It's easy to reproduce, it happens every time.

So I decided to pull out my data logger.

I know 3 degrees of KR isn't anything to worry but I can feel it and its annoying.

I wonder if anyone else feels this?

FYI - I am running 91 octane (that's all we get in CA).

A 91 tune will fix it for sure, not sure if I'm ready for that yet.

Click for larger image

[TRZ06]

GM has done that for as long as I have had them. My C5 Z06 was very sensitive.

You can actually hear the exhaust tone and sound change when it happens. Even more pronounced when you have an aftermarket exhaust. The exhaust note gets more muffled and loses treble and it has a more snappy/sputter sound to it. Very apparent with my Corsa system. The sound is never consistant and changes tonality all the time.

Oddly when I have the AC on, it tends to have a more consistent sound quality, but that is probably because of the extra load from the AC compressor.

[BMWM.D.]

I’ve never noticed that, but I got KR around that RPM in the 3-4 degree range when I was doing my stock baseline dyno pull on 91. There was a dip in the torque curve when it occurred.

[590_The_Judge]

Try a different brand fuel ��*♂️ In socal mine is cranky if im not using chevron or mobil...

[angryBits]

Originally Posted by TRZ06

GM has done that for as long as I have had them. My C5 Z06 was very sensitive.

You can actually hear the exhaust tone and sound change when it happens. Even more pronounced when you have an aftermarket exhaust. The exhaust note gets more muffled and loses treble and it has a more snappy/sputter sound to it. Very apparent with my Corsa system. The sound is never consistant and changes tonality all the time.

Oddly when I have the AC on, it tends to have a more consistent sound quality, but that is probably because of the extra load from the AC compressor.

Good to know I'm not alone.

My C7 Z06 did it, but it suffered from other problems so I figured it was related to that and not normal.

My Gen5 ZL1 had audible knocking so I had to get it tuned for 91 and the problem went away.

No love for 91 octane :(

[angryBits]

Originally Posted by BMWM.D.

I’ve never noticed that, but I got KR around that RPM in the 3-4 degree range when I was doing my stock baseline dyno pull on 91. There was a dip in the torque curve when it occurred.

The dip doesn't do it justice, I expected more given how apparent it feels in the seat.

Did you get a tune? Did it go away?

Thanks

[angryBits]

Originally Posted by 590_The_Judge

Try a different brand fuel ��*♂️ In socal mine is cranky if im not using chevron or mobil...

I typically go to Shell, but there's a Chevron inconveniently across the street. I can try it.

Gas should follow rigorous standards -- I suppose a little more moisture can accumulate at once station vs another if they're lazy about cycling the gas.

[arpad_m]

Originally Posted by angryBits

The dip doesn't do it justice, I expected more given how apparent it feels in the seat.

Looks like a solid 15+ lb-ft to me, so it definitely isn't negligible

[TRZ06]

Originally Posted by angryBits

I typically go to Shell, but there's a Chevron inconveniently across the street. I can try it.

Gas should follow rigorous standards -- I suppose a little more moisture can accumulate at once station vs another if they're lazy about cycling the gas.

Being from the Bay Area, I am sure you know about Sunol Super Stop Gas station?

They have 94, 96, 98, 100 Octane in the middle row pump

I try to hit it up for 94 Octane any time I am in that area.

[BMWM.D.]

Originally Posted by angryBits

The dip doesn't do it justice, I expected more given how apparent it feels in the seat.

Did you get a tune? Did it go away?

Thanks

I run a half bottle of Torco every tank, but my car is also modified and tuned at this point. I’ve messed with a whole lot of settings (Driver Demand tables being a big one). These engines are octane sensitive for sure though.

There really isn’t a magic tuning fix for this in my opinion. You can remove timing in that area to get rid of KR, but that’s going to hurt power as well. But like I said before, I can’t feel it. If I didn’t do my own tuning, I’d have zero idea it was going on. Maybe it’s because I have an A10, or maybe you’re feeling something different.

Logging and tuning these things is way different than say a Gen 4 engine. There’s a lot going on. Are you at WOT on this log? A bunch of the throttle PIDs never show 100%. To me it looks like it based on the commanded throttle actuator reading, along with the MAF airflow. I found a bunch of the default PIDs to be wrong or inaccurate. Took a while to get it all dialed in.

[angryBits]

Originally Posted by TRZ06

Being from the Bay Area, I am sure you know about Sunol Super Stop Gas station?

They have 94, 96, 98, 100 Octane in the middle row pump

I try to hit it up for 94 Octane any time I am in that area.

I've heard of it but never been. I didn't know they had 94, I'll check it out.

There's one in Redwood City that has 100 octane.
I'd usually take about 20 gallons home with me in gas cans and then mix in a few gallons with 91 in my Z06 and Gen5 ZL1. I haven't done that yet with my Gen6 ZL1.

[angryBits]

Originally Posted by BMWM.D.

I run a half bottle of Torco every tank, but my car is also modified and tuned at this point. I’ve messed with a whole lot of settings (Driver Demand tables being a big one). These engines are octane sensitive for sure though.

There really isn’t a magic tuning fix for this in my opinion. You can remove timing in that area to get rid of KR, but that’s going to hurt power as well. But like I said before, I can’t feel it. If I didn’t do my own tuning, I’d have zero idea it was going on. Maybe it’s because I have an A10, or maybe you’re feeling something different.

Logging and tuning these things is way different than say a Gen 4 engine. There’s a lot going on. Are you at WOT on this log? A bunch of the throttle PIDs never show 100%. To me it looks like it based on the commanded throttle actuator reading, along with the MAF airflow. I found a bunch of the default PIDs to be wrong or inaccurate. Took a while to get it all dialed in.

I ran Torco in my Z06 for awhile but heard some bad rumors so I stopped. I honestly don't believe it's harmful but didn't want to take any chances. Whats your take on Torco?

The gas pedal wasn't to the floor but close.