Quote:
Originally Posted by shifterboy45
this is a very good discussion of some of the basics required to accurately tune a car. but there is something i would like to add as food for thought...
unless you find the optimal road conditions, and use them for every test, every run.. your documented results will vary from a little to a whole hell of a lot. this includes ambient temp, generated road heat, traction, or lack of it ...
thats only if you want to be accurate and reproducible
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Glad you piped in shifterboy......
I do use the exact same stretch of (safe) road each time I datalog so I try to keep as many of the variables as constant as I can control.
But it's hard to control the weather.
I have tried......but failed!
In any case, the timing logs do vary a bit from run to run so what I shoot for in dialing in is to see whether the majority of my timing logs for identical boost and ignition correction tend to be smooth, spike free and upward sloping to 11+ degrees by around 6K rpm.
So if one out of three logs has a single 3 degree dip, but the other two logs are knock-free then I feel pretty good that my settings are close enough to make me comfortable for how I drive on the street.
I generally will not do more than a 3rd to 4th gear WOT on the highway in daily driving....so that is what I log.
A single gear log is not enough as CBR335 pointed out......heat is cummulative, so you need a couple of gears, or a long 4th gear pull.
I try to use the worst-case scenario by heat-soaking the engine with a couple of prliminary pulls before I do my datalog, because generally I find you get less knock on a cool engine than one that has been thermally challenged.
Of course weather changes all the time, so the case is made for autotune here.
But because no one has really answered the question as to how much knock is considered "normal" and acceptable, I prefer to get as little of it as possible.
Even autotune averages the number of knock events before adjusting the tuning parameters, so in some sense it is initially reactive before becoming proactive.
Does that make any sense?