poor fuel milage

[NancysToy]

Colder air is denser as you mentioned, but it is much easier to cause an ignition when there is more air available. Because the air is denser and thus more abundant, more air fits within the combustion chamber, making ignition easier. Should require less fuel. Air density at 120° is about 20% lower than density at 30° (this is not an exaggerated seasonal temperature difference for Vegas). This is an almost direct correlation to the approximately 20% decrease in fuel milage I see in the summer months. Instead of adding more fuel to achieve the needed fuel to air ratio, wouldn't it make more sense to allow less air in instead to achieve the desired ratio?

Unfortunately, the sensors and the fuel maps work only off the air pressure and temperature (indirectly calculating air density) and a fixed air-fuel ratio in the mapping. The ECM fine tunes this under certain conditions. How well the mixture fires in the cylinder doesn't matter...only whether or not there is excess fuel in the exhaust during closed loop operation. Perhaps a system could be designed to monitor combustion efficiency and compensate for it, but it doesn't exist on the Spyder. Also keep in mind that the air temperature is not the combustion chamber temperature, which is quite constant once the engine warms up, so combustion efficiencies remain fairly constant. The ratio you have seen is merely coincidence, IMO.

 

[shelbydave]

Unfortunately, the sensors and the fuel maps work only off the air pressure and temperature (indirectly calculating air density) and a fixed air-fuel ratio in the mapping. The ECM fine tunes this under certain conditions. How well the mixture fires in the cylinder doesn't matter...only whether or not there is excess fuel in the exhaust during closed loop operation. Perhaps a system could be designed to monitor combustion efficiency and compensate for it, but it doesn't exist on the Spyder. Also keep in mind that the air temperature is not the combustion chamber temperature, which is quite constant once the engine warms up, so combustion efficiencies remain fairly constant. The ratio you have seen is merely coincidence, IMO.

Wouldn't the combustion chamber temp vary with the type of driving? I know my EGT's go way up under hard acceleration.

 

[NancysToy]

Wouldn't the combustion chamber temp vary with the type of driving? I know my EGT's go way up under hard acceleration.

It can, but the chamber temp doesn't vary as much as you think. The water-cooled head keeps things pretty constant. The exhaust gas temp is another story, that can vary considerably.

 

[Some Guy]

Hi Scotty,
I claim no intelligent knowledge in this conversation. What do you think about the Power Commander V With Auto Tune?

 

[rock]

we have a 2010 rts-se5 limited ...it started with low mileage also about 26 mpg...at about 10000 miles it increased to 31 mpg...at 15000 miles we put a k+n air filter and a good exhaust on it and now get close to 38 mpg ... thats with me n the wife on it.. we now have 22000 miles on this unit and are thrilled and will never own any other machine but a spyder...so b patient it will come around...also shifting rpms are everything....AK is right around 5000 rpms is an excellent rpm to run the unit at ,,shifting and cruising...be a gentle and safe rider and dont abuse this unit and you will get a life time of pleasure ...good luck and happy riding!!!!