C6Z06 surge/bucking from 1700-2000 rpms

[LegoZ]

Hey all.

Having an issue with surging/bucking at part throttle cruising. Gone through everything I can think of and I think I am going crossed eyed trying to figure it out.

Would some one mind looking at the files and point me in the right direction?

Thanks!

Dave

2006 c6z current file as of 9-28-19 After MAF TUNING SETTINGS REV 3 FINAL.hpt

9-28-19 scan log.hpl

P.s
Heads are TSP PRC 265's

Cam is TSP Stage 2.2 Cam Specs: 234/246, .635"/.635", 112.5 LSA, 109.5 ICL

Stock Intake, Air Intake and Stock Exhaust (for now)

[SlowNStock]

Log a drive cycle with some bucking, then adjust timing in the offending areas. A quick and easy way to clean up light bucking is by pulling a few degrees in the cruise areas to get more load for a given RPM.

Adding timing can also help (until you go beyond MBT), but can exacerbate other instabilities (airflow, fuel) - usually (a lot) more work to go that route.



The other thing I look for is any area where bucking occurs that fall on a steep(ish) part of the ignition map. Take a hypothetical example of bucking occurring around 1200-1600 RPMs and 0.32 g/cyl.

Looking at the adjacent cells vertically (0.28 and 0.36 g/cyl), there's a swing of 4 degrees of timing in each direction - fine for a stock engine, maybe too much for a substantial cam at that load. Taking the idea of pulling timing to reduce bucking and rolling it with the idea of smoothing out the low load areas around cruise, something like below could be a good start - simply the stock map with the 1200-1600 RPM, 0.32 g/cyl cells copied into the 0.28 g/cyl cells, then the boundaries interpolated.

Stock Map: Attachment 93460

Hypothetical Trial Tune: Spark Example Cons.PNG


You can also go the other direction - more internal EGR lends to more timing to achieve MBT, so adding advance isn't unreasonable; the trick is making sure you don't go beyond MBT.

Hypothetical Advanced Tune: Spark Example 2.PNG

[LegoZ]

Thank you,

I kept thinking it was more of an airflow issue than spark (got stuck in the weeds tuning the MAF). Looking at my HI Octane table, I can see where there are some fairly substantial jumps between cells in the part throttle cruise areas. I will go log it and clean up the areas causing the problems. It is the last thing I'm trying to get dialed in before moving on to VE.

[Ben Charles]

Spark and fuel will fix 100% of it on cam that size

[LegoZ]

So, adjusted some areas that had big jumps in spark from cell to cell. Need to tweak/fine tune a couple more and log it again. But, it is SOOOOOOOOOOOOOOO much better, completely different car. Now to get the Wideband hooked up and dial it in.

SlowNStock: Thank you for the well thought out and conveyed reply! Appreciate it!!

Dave

[SlowNStock]

No problem, glad to hear you're off in the right direction