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Pumpgas to E85 - injection and ignition

Flex Fuel Tuning

Discussion and questions related to the course Flex Fuel Tuning

Page 1

Hi there,

I have a question regarding switching from pumpgas (102 octane) to E85.

The question is related to make a kind of basemap.

For injection, I know to add 30% to 35% of fuel.

But how much can I safe add ignition so that I have a start point for mapping?

I know that finally it must be done on the dyno, but is there a value which I can add to that table? (e.g. 4 degrees or 20%)

As E85 is by far not so knock limited like pumpgas, there should be not so high risk.

Thanx alot :-)

Best regards


The percentage of increase in injector flow required for lambda to be the same, is relative to the ethanol content percentage.

30% more flow might be around 50% ethanol / pump gas blend, where 85% ethanol content might be closer to 50% more flow.

generally if your timing is torquey but not misfiring on pump gas, then it will be fine for ethanol blends.

on some engines with high ethanol content fuel, you can increase timing beyond MBT, and to the point of lifting the heads ; good-bye head gasket.

if you know you're near MBT on pump gas, you'll be well-off for starting with ethanol blends.