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lean AFR

EFI Tuning Fundamentals

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I still don't quite understand how lean fuel mixture can be advantageous for endurance racing. Also maybe explain a pitstop advantage maybe that could help me understand better. Thank You!

Imagine two tunes, one that can go 20 laps on a tank of fuel, and another leaner tune that can go 21 laps ( just 5% more efficient). The first tune needs 22 tanks of fuel to go 440 laps (so 20 refueling stops) but the second one only needs (440/21 =) 20.95 tanks, so only 19 stops. If both tunes can run the same lap time, the leaner tune will be ahead by the length of a pit stop.

hope that helps.

Yup, the whole thing is a juggling act, balancing many different things.

For instance,time lost in pit entry, refueling, fitting tyres, swapping drivers, etc, all takes away time on the track, so the teams will try and minimise those - if they can cut out one stop, that can be 30 seconds of track time gained.

Every tyre change takes time, so it is common to do 3 or 4 fueling stints per set of tyres. If the tyre wear is such that it lies between the 3 or 4, there may be a choice of short fueling (not filling the tank right up) and/or running full power rich and just doing 3, or filling the tank right up and running slightly leaner and possibly stretching it to 4. The latter gains track time which has to be compared to losing a little lap time. many race series also have limits on how many sets of tyres can be used, so that's another reason they may try to eek out laps.

If there are two, or three, drivers there will normally be a minimum and maximum 'seat time' for each driver, so it's common to have the driver change correspond to a fuel stop and change tyres at the same time.

Under some circumstances, such as rain causing the track to be a little slippery, maximum power may not be useable so by dialing it back a little they can go further.

In traffic, especially if one can take advantage of the car(s) in front reducing the drag on the car, less power is required and the engine can be run a little leaner, possibly with the expectation of having a little more fuel to 'over-cut' the other car(s) when they're forced to refuel.

Using David's example above, actually 18 Vs 19 stops, if one assumes 4 stints then tyres would be swapped at the 3rd, 7th, 11th, 15th and 19th pitting' for either option, but the more economical vehicle would have the advantage of fresh tyres going into the last stint of 63 laps whereas the other would have a full 80 laps to do and so already have 17 laps on the tyres if there's a sprint finish. The driver may also be fresher.