I have had an idea running around through my brain and wanted to pass this by the folks here... The following are assumed: - VEs have already been corrected by a few VTune sessions to the point where there is little difference between VTune runs. - After all VEs have been corrected, adjustments have been made to the spark tables (assume that timing increases were made for the sake of discussion - say 3 degrees for testing). - Any fast retard has been corrected by doing data collection runs and making any adjustments (perhaps optional, but seems reasonable to do so). Now the manual tells us to re-run VTune as the VEs may have changed since the spark advance has been adjusted. So here's the question: If you compared the VEs before making timing adjustments with the VEs after timing adjustments and subsequent VTune sessions were made (you could use a spreadsheet), if you lost efficiency in some cells, couldn't you draw the conclusion that the change in spark caused a decrease in efficiency, and therefore less timing would be needed? And also, if the change resulted in increased efficiency, couldn't you draw the conclusion that the increase in timing helped? Basically, can we use this information to determine if the change in spark was well received or not? This differs from instructions that state to increase until fast retard kicks in and then back off. By noting differences in VEs after more VTune runs, I would think this could be an aid. The only thing is that VEs are TP based and spark is MAP based... Thoughts? Am I nuts?
So if you add spark and it becomes less efficient, did it not like that spark advance? This is what I'm trying to figure out... If you add spark and it became more efficient, is that an improvement?
Inquiring minds want to know!
I'm just trying to figure this all out...
You need to remember the VE number is calculated from the tailpipe back not measured from the throttle body forward. The system does not have Mass Air Flow sensor in it to measure the volume of air going into the engine.
If your cylinder filled to 100% (Volumetric Efficiency of 100) every time and it burnt perfectly at 14.7:1 and the O2 sensor agreed it was 14.7:1 and gave it the thumbs up your Vtune would reflect a VE of 100.
Without changing anything else you quite stupidly retard the timing 30 degrees. The same amount of air enters the cylinder (100 VE still just like the map says) the injector fires off the same amount of fuel and as the exhaust valve opens the partially burnt mixture rushes past the O2 sensor and the O2 sensors goes WTF!!!! The O2 sensor tells the VTune that there is no way we have a VE of 100 at this point wind that back to 33 and try again.
Yes the spark timing effects the calculated VE but it doesnt effect the amount of air entering the engine. The VE is just a number. If more spark makes the bike feel nice, or better still make more hp on a dyno or at a dragstrip awesome. If the VE number changes up or down as a result of this BIG DEAL!
cheers Surly
Fuzk!!! I don't understand this spark shit at all !!!
