I get what you're saying, we're cramming more air and fuel into the same space... But wouldn't that be easier to ignite as it's compressed? (no, harder) The motor's compression ratio is unchanged, but with more mass (a denser mixture) the combustion chamber sees higher pressure, which should be exacerbated by timing advance, right? And an air/fuel mixture becomes easier to ignite as it is compressed, even going as far as self-igniting under high enough pressure (as in diesel engines.) (Dieseling is when things go wrong for us. We are always striving to control the heat genrated by compression)
Yes, your logic here is correct and it is one of the issues we fight to control when we are trying to increase power. The heat of compression can cause the charge to ignite before we want it to. So we take steps to prevent this from happening. We do things to cool the charge (intercoolers and water meth for example). We use higher octane fuel to retard its ability to ignite. Essentially we don't want to burn the charge until the perfect moment to get the most power, so we are looking for control.
So is the issue that it is harder for the spark to jump the gap when under higher pressure? Or in a more fuel-dense mixture? Not necessarily richer, but since air can be compressed and liquid fuel cannot, the fuel should be occupying more volume as the piston approaches the top of the compression stroke.
As mentioned above we do a lot to prevent the charge from burning up until we want it to burn. When we are ready for it to burn we want the burn to be immediate and complete. The gap of the plug has a direct relationship to the actual temp of the spark plug tip. It will take a better spark to overcome the cooling and higher octane fueling (if used). Also a denser charge is not easier to ignite with a spark. Greater density of charge will require a hotter spark.
Thank you for the responses, I'm just trying to wrap my head around the logic, not argue. I'm not having an issue with misfires, on the contrary I just logged today and had no misfires without reducing the gaps. I realize that the gaps tend to open over time and it may become an issue later, but I was expecting to at least see occasional isolated misfires.
I didn't think you were trying to do anything but understand. I was asking the same questions at one point. I am not a tuner and hopefully others will correct any of my statements and add to the information about how we use spark plug gaps as part of a performance tune.
