C6 with a low RMP surging issue

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I have a 2012 procharged C6 corvette with an E38 and LS3 with a M6. Cam is a 230/250 116 and has about 8 degrees of overlap. When I bought the car a few months ago, it was tuned MAF only and had some drivability issues. Car ran very rich everywhere and had a low RPM surge. I went to a 2 BAR OS thinking the cam may not be behaving well with the MAF at low RPM. I'm a novice tuner so its been a steep learning curve but its slowly coming together. The issue I?m having is that I have a buck or surge at light throttle from 1000 to 1500 RPM. Doesn?t matter if the engine is hot or cold or what speed I?m at. The surging is much more pronounced in lower gears but is noticeable all gears. On occasion, at low speeds like creeping through a parking lot, the car will surge bad enough that I have to feather the clutch to get it to settle down. Being that my fueling in that area is very close, I?m struggling to figure this out. I have pulled several degrees of timing in that area, at roughly 3 degrees each time and the surging has gotten a little better but its still there. I'm just not sure how much more timing I can continue to pull or even if that's the best approach. Would you guys happen to have any suggestions?

What injectors do you have in it? Looking at the log it's most likely trims, injector control and plain ol' cam reversion.

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Originally Posted by edcmat-l1

what injectors do you have in it? Looking at the log it's most likely trims, injector control and plain ol' cam reversion.

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id 1300

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Originally Posted by ta406

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I have a 2012 procharged C6 corvette with an E38 and LS3 with a M6. Cam is a 230/250 116 and has about 8 degrees of overlap. When I bought the car a few months ago, it was tuned MAF only and had some drivability issues. Car ran very rich everywhere and had a low RPM surge. I went to a 2 BAR OS thinking the cam may not be behaving well with the MAF at low RPM. I'm a novice tuner so its been a steep learning curve but its slowly coming together. The issue I?m having is that I have a buck or surge at light throttle from 1000 to 1500 RPM. Doesn?t matter if the engine is hot or cold or what speed I?m at. The surging is much more pronounced in lower gears but is noticeable all gears. On occasion, at low speeds like creeping through a parking lot, the car will surge bad enough that I have to feather the clutch to get it to settle down. Being that my fueling in that area is very close, I?m struggling to figure this out. I have pulled several degrees of timing in that area, at roughly 3 degrees each time and the surging has gotten a little better but its still there. I'm just not sure how much more timing I can continue to pull or even if that's the best approach. Would you guys happen to have any suggestions?

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The VE could be better and the spark smoothing should be turned off.

You can also try it in open loop to see if you need to tweek o2 response as that can start a surge in a car like this..

But your log was at 1200 RPM at 12 mph or so.. This is exactly where this thing is going to buck especially with this cam. If everything is perfect I'd still expect it to surge and buck.

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Originally Posted by ta406

id 1300

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Injectors that big will only make the feeling worse even with perfect data. The change in pulse width as the trims swing can be felt. That why Alvin mentioned trying it in open loop. To take that swing out of it.

Trying to control big ass injectors at low pulse widths/idle is like trying to fill a shot glass with a fire hose. That's my line. Y'all can borrow it if ya want LOL

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Originally Posted by edcmat-l1

Injectors that big will only make the feeling worse even with perfect data. The change in pulse width as the trims swing can be felt. That why Alvin mentioned trying it in open loop. To take that swing out of it.

Trying to control big ass injectors at low pulse widths/idle is like trying to fill a shot glass with a fire hose. That's my line. Y'all can borrow it if ya wont LOL

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No one will admit it but cars will make better power with properly sized injectors too. I've proven it more than a couple times.

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Thank you for the suggestions. I was finally able to get another log. This is open loop with spark smoothing disabled. The bucking was noticeably worse. As far as injector size, I'm running an f1c blower and plan to run E85 at some point in the future. The injectors were on the car when I bought it and would step down if that would solve the problem.

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Originally Posted by Alvin

No one will admit it but cars will make better power with properly sized injectors too. I've proven it more than a couple times.

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Is this following the generally accepted 80% IDC at WOT? Or something different?

I would re-enable the maf for testing, and for another datapoint to compare against for airflow, judging by the MAF HZ, i dont see much or any reversion in the problem areas. I would also change your VE table axis for way higher resolution, and just stay out of boost until you can get fueling tighter in that area. Seems a pretty high increase from 60kpa to 65kpa around 1200 rpm, you can watch your DynAir jump 2 g/s in between those cells. I doubt thats true. Those injectors should idle just fine. After you can confirm your AF models to be good, then I would go back after timing, try 1 to 2 degrees at a time, not 3. and make sure it is smooth in surrounding areas. It is always going to buck, but i feel like that size of cam with the wide LSA should be a little more tame.

Getting the fueling as close to perfect in your problem area is about as good as your gonna do. I thought it was strange you said it was worse in open loop, but then noticed the LTFT pulling 50% in an attempt to satisfy the NBO2s.

There are a bunch of little adjustments to try but the fueling is gonna be number one on the list. The fire hose and shot glass analogy is spot on in this case and when you had flow reversion from valve event overlap things get worse. There is a reason race cars don't idle at a very low rpm.