who's there?
jk...
As promised, here is a datalog from last night's 120.3mph run at Sac raceway:
Running 17-18psi of boost on straight 100oct fuel. Which is pretty aggressive. Usually when you run too aggressive of a map, you get evidence of knock retard in the midrange to upper rpm range. But one thing I noticed was seeing knock retard in the datalogs right after the shift (and once in the middle of 3rd great at time stamp ~31s). The green circles show the knock retard points. The 1st at 3rd knock retard point can be considered knock retard because actual ignition advance at that point is just 2-3 degrees. After that event, timing stays reasonably low with a very gentle upwards slope.
Turns out the reason for the post shift knock retard was caused by a very short term timing spike (see in red circles). If you look at the boost pressure (in the manifold... not shown) during these timing spikes, you'd see 10-11psi. And those who have spent a fair amount of timing logging these engines knows that 10-20 degrees of ignition advance at over 10psi of boost at 4500-5000rpm is a recipe for knock. Even on 100oct. And sure enough, reality mirrored theory. With most of my run hampered by knock retard activity, it's still surprising that it ran as fast as it did.
But the next question is: How do we fix it? Sure, we can probably run MS109 and cool the charge down with meth. But that doesn't solve the problem when we are running on pump gas (on a lower boost map, of course!). So the real solution would be to tune out the timing spike with the PROcede's timing control/CPS offsetting feature.
See next post
