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Increased ingnition timing on e85 causing negative trims

Road Tuning

Discussion and questions related to the course Road Tuning


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Recently added a few more degrees of low load timing to my WRX. It's on e85. The maf was scaled very well before the increase. But post timing increase the trims were between 4 and 9% negative. So less fuel required for a given amount of air entering the system to get stoic. Therefore can I assume the car is more efficient achieving a more complete burn with less fuel. Torque has definetly increased indicating it was behind MBT. As road tuning only the seat/arse dyno used. Boost leaks negative nil other changes to the set up so I'm rescaling the low load maf. Could it be true? More power with less fuel from utilising the higher octane fuel? I wasn't aware that timing changes would affect fueling that much. Any input would be appreciated.

The ignition timing shouldn't have any effect on your air fuel ratio so I'm struggling to explain what you're seeing. Remember that the air fuel ratio is simply the mass of air and mass of fuel in the cylinder and this is fixed at the point the intake valves close. Understandably then it is unlikely that the ignition event can actually change the air fuel ratio.

Is the negative trim repeatable in that exact area of engine operation? If you remove that timing and test again is the trim back to zero (or close to it)?

I agree with you Andre and that is why I asked. I did however see it. there were no setup changes, added timing about 3 deg in cruise then had -7% trims. It was low load cruise with quite a bit of overlap with cam timing. I will flash back and forth when I get the chance and double check. I'll let you know.

Keep me in the loop when you get a chance to test. I'm interested to hear what you find.