While messing with my tune through Power Vision / WinPV I loaded up a copy of my stock tune out of curiosity to compare. I'm currently running a modified (both through auto tune and some manual tweaks) tune from FuelMoto. My bike is a 2013 Dyna SuperGlide Custom with Thunderheader and open air filter. Recently I have been adding small tweaks to my spark advance tables just trying to smooth everything out. I noticed that when comparing my spark advance tables to the stock tune that my stock tune has much more advanced timing (+9 at times) right around the cruise range. For some reason I would have thought there would be more timing with the modified tune. My assumption would be that more air + more gas would demand more spark.

Definitely not an expert here so any help would be appreciated.

-Steve

Edit: I'm comparing the stock spark advance tables to the tables in the FM tune before any of my tweaks.

 

Not exactly.... During low load/part throttle conditions, engine vacuum is increased and the VE is very low. This decreases cylinder fill and effectively lowers compression. The low air density decreases the speed at which the air fuel mixture burns and requires more timing to complete combustion. If you have made modifications that increase you airflow at low PRM it would allow you to run slightly less timing due the greater cylinder fill.

 

Thanks! I did some more research myself (google is your friend) and with that and your explanation I think I understand it a little better. Always nice to know what is going on instead of just blindly changing values hoping to get lucky.

Thanks again.

-Steve