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Which Gear do you set fuel/VE for?

EFI Tuning Fundamentals

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I noticed that with the same fuel and VE my O2 reads differently with the same load along the vertical scale with different gearing.

1st gear is moving towards lean and gets richer as gears increase.

See file attached

Attached Files

(very badly described from experience to date)

do the tuning in a gear closest to 1:1 ratio (4th gear is usually close in a 5 speed)

reason is that if you do the tuning there under full load for each cell - those will be the worse case conditions - it might get leaner in lower gears but it shouldnt get richer in higher gears (or knock in higher gears as steady state tuning is "worst case" already) - in theory anything after the 1:1 gear should be the same af ratio (eg 4, 5 and 6th should be very close on a dyno without ram air effects of high speed air hitting the engine bay)

in lower gears - the engine revs too quickly for the fueling to keep up accurately compared to the steady state tuning done - i get that in my honda (around 1.7 sec from low revs to redline under street driving conditions in 1st) - by the time the ecu injects fuel for those revs - the engine has already blown past that point and is now "lean" (people who know more could explain it better - fuel inlet runner puddles - ecu latency - blahblahblah)

the ecu i use has a 3d fuel correction table by gear i can apply - very roughly i need to add around 4ish% extra fuel in full load ramping conditions to keep the af closeish to target

you could try to move the o2 as close as is safe (depends on na or turbo and what lifespan your wanting on the sensor i guess) to the exhaust ports to get a response with less latency but it wont cure the issue of the engine revving faster than the fuel can keep up with in lower gears.

ve shouldnt change - just the gear correction tables should let you get things happy again

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