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Start of Injection ethanol

Flex Fuel Tuning

Discussion and questions related to the course Flex Fuel Tuning

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Hey guys, I have a 2015 wrx with full bolt ons and have finished my 93 tune. I will be moving onto different ethanol blends soon and was wondering if there are any specific rules for start of injection changes with higher ethanol content. Obviously I am going to give the car what it wants but was just wondering if there is any pattern I should know about before I start. This is the only part that I am unsure of and would like some help.

I don't usually make significant changes to the injection timing in comparison to a pump gas tune but of course the dyno will tell you what the engine wants. Obviously you're going to be holding the injector open for longer so you could take this into account. Most often with a PI engine I'll set the injector timing based on EOI rather than SOI so that's just worth mentioning since the two modes will give you vastly different actual injection timing patterns.

With a large number of flex fuel systems being sized so that the injector duty cycle is hitting perhaps 80-90% under high load conditions, there's understandably not a lot to be gained in injection timing since the injectors are almost open all the time anyway. The bigger gains are usually in the idle and cruise areas where IDC is much lower.