I labeled this as all three engines for easy searching and because it should be applicable to all VVT. Threads on cam timing are well-documented. I did the standard tuning months ago after reading those threads. But, yesterday a though crossed my mind. It is known that overlap at cruise rpm is used to increase gas mileage. Power gains were found while maintaining good gas mileage by decreasing the overlap. Here's where my thoughts came in.
For autox, drags, and road racing, who cares about mileage? Irrelevant. In that case, reducing overlap should increase midrange power. This thought had already occurred to MikeM awhile ago I guess while I was busy pondering other parts of the LNF.
My methods of testing are similar to what others posted on here. But, I use a method that gives me the most repeatability. I see comparisons of 60-100 times, but my shift points are still 6-6.25k rpm. For this reason, I floor it at 58-60mph and measure 63-83mph times. This ensures a steady-state condition whereby the only difference may be the flatness of the road (lifting is at 85mph). All done on my local closed Mexican highway with professional driver, of course. I average several pulls to determine whether or not changes are good or bad. I have tested this way for months for comparisons. So, I know results are reasonably accurate.
As a refresher, here are the stock cam tables (09 GXP, warm cam tables):
stock cam timing.png
Nice, clean, and smooth because GM engineer.
Here is what my final tune was based off of the increased midrange torque versus good gas mileage. This took me a couple months of tuning to get around to with testing:
tuned cam timing.png
Pretty typical adjustments which can be reached after reading through the cam timing threads.
Finally, here is what I tested yesterday. Flattened the midrange overlap 'hump' on both profiles to focus solely on power gains:
race cam timing.png
To guarantee that I wasn't cheating with any downhill runs, I made absolutely sure that all four pulls were on slight inclines or better. I used inclines only if they were clearly visible as uphill. This was on my 91 octane tune (11° peak timing). Results on my two best pulls showed equal 63-83mph times as my 100 octane tune (18° peak timing). In time, the gains were 0.2-0.3sec on slight inclines. Worst two pulls were 0.1sec improvements with steeper inclines and/or turns.
0.2sec on a slight incline in a 20mph window is a pretty significant gain. It definitely didn't feel faster. Just smoother. On a gas mileage note, my cruise mpg didn't suffer significantly, though I did have to recalibrate to a new rpm/speed at which my mileage was best. You can feel that the car doesn't freewheel as much when lifting.
Something people may want to explore on tunes for the track versus just all-around. I'll do more testing this weekend to reaffirm what I've found so far. Thoughts and comments welcome.
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