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post #6 of (permalink) Old 01-19-2016
pir4te's Avatar
Joined: Jan 2016
Posts: 2
E85 Write Up

Ok, gist is unless you have fuel sensor you are flirting with danger, buy a known fuel if you are racing and that will save you having to test fuel composition manually and retune before the race. Obvious, isn't it?
The important point is that ethanol gives a safety margin, this article implies e50 vs e85 does reduce it. Which is incorrect unless you have high effective dynamic compression (natural or supercharged) and chasing MBT on knife edge with no safety margin (or engine protection) as you say.
With typical static comp (10.5 CR NA or 9 CR + 9psi) there is virtually no difference in knock resistance and 1-2% power output between e50 and e85. Add racecar cam with longer duration or turbo cam and it will have significantly less effective dynamic CR on most engines (LIVC and wide LSA).
Even if tune uses an aggressive spark map and AFR becomes incorrect because there's actually less ethanol fraction at the pump, that means it will run richer, not more lean.
Spark variance may be +/- but won't blow up or melt unless engine protection (KR) is disabled.
Without going into Weibe curves and Mass Fraction Burn of ethanol under compression (some good papers available, pm me), likely with high ethanol spark is retarded with high comp, advanced with normal comp, so ethanol variation in either case is not dangerous just not optimal, as is tuning without sensor.
But the concern over rusting injectors and letting your car sit with some ethanol left in it is obviously in regard to non-alcohol compatible units anyway. It's a Furphy, like using a flexible fuel specification without the requisite feedback sensor.
It's obvious, not really insightful unless you thought e85 (flex fuel) at the pump means always 85% ethanol. Not really everything you wanted to know about alcohol from an aftermarket fuel component specialist, rather contrary and banal, like a specialist tyre consultant company (that charges more than anyone else) commenting on disasters that can happen if you drive over rough terrain with drag rubber on your 4x4.
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