Quote:
Originally Posted by elhigh
I thought the presence of ethanol increased the octane, not lowered it. I understand you can jack the compression on an engine that only ever runs E85 up to crazy high levels with no risk of detonation. I don't know what the ignition thresholds are like for ethanol but I reckon if it's harder to ping, it's probably a little harder to light, too. I'm just taking a flyer here, but I would think ethanol would benefit from a hotter plug, not colder.
OP is taking advantage of his computer's programming to maximize economy with a colder plug, which permits more advance and therefore a more complete burn.
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Running e85 allows you to run more power ie timing, compression, boost, ect. You can run a hotter plug with it but if you want to take advantage of it run a colder plug and adjust timing, compression, boost near knock threshold fore more complete burn.
Correct...I am trying to take advantage of the oem tune with 87 octane. With this somewhat high compression(11:1) engine it is easier for knock to be triggered. Also seems the tune is on the edge for best fuel economy in areas which was having slight knock. Seemed like any area high load where computer did not richen fuel up it would start ticking and knocking. I do not think going colder than this will help as I should not be losing any power through knock at this point and taking advantage of oem tune and 87 octane. Now if I can change to colder thermostat or fool ecu with resistors on coolant temps, iats, ect it may make it adjust more timing with no knock. However it will also adjust afrs, fuel pressure, cams open/close, ect. The tech in this little engine scares me right now so I am taking it slow and learning how it works and responds to things daily via scan tool live data before planning next mod...
Computer on this thing is strange. Hard as heck to go open loop. Have to be in gear down a pretty steep grade for several seconds and if using cruise control seems to want you at least 3-5mph over set speed before it will go open loop dfco. And at wot open loop will only happen in very high rpms and sometimes not in lower gears. It will however stay closed loop and richen mixture slightly at same time which is why I say it is weird. Afrs go to mid 11's during wot open loop.
I would also like to add that dealer told me that it was not knock but sound of gdi engine and high fuel injection pressure. They are right about high fip as it idles around 60psi and goes to max of around 2200psi under high load. They were wrong about it not being knock as the sound is gone and pretty much everything except for timing in certain areas changed.