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How does ford calculate MBT timing from factory? Is it based off race fuel at a certain temperature? 

 

With ethanol unlikely to reach knock in lower loads (0-1.5 loads etc) should we be aiming to achieve MBT in our borderline knock table, obviously logging knock retard to make sure it's all ok?

 

Also with running a bigger turbo than standard (FG xr) is it better to use MBT calibrations from the vehicle it is designed for or to use one say from an f6 or sprint that have the higher loads already  and reinterpolated to suit any load scale adjustments?

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Yes I believe that is what they do. It is done at SAE conditions then they have coolant, lambda and intake temp modifiers multiplied on top.

MBT will be slightly higher with ethanol as it has a slower flame speed, however the stock MBT is a great gauge to use.

Something to be aware of is as soon as you change the turbocharger you change the backpressure and hence you change the MBT for the entire load scale making the factory calculation a guide at best. Because of this you can't simply chop and change between a sprint cal (with a GT3582) and a standard FG XR6T with a GT3576

Ultimately unless you have a dyno load cell and set up real time tuning you won't be recalculating MBT any time soon. So your best bet is to leave the stock MBT, work out your MBT at your max load row, then interpolate between the factory max load and your new max load. Because you are doing this on your actual real fuel, you are effectively making your MBT and borderline knock tables equal which is what you see in most aftermarket tunes. To do the spark tune properly like Ford do would take you thousands of litres of fuel and weeks of dyno time.

Also have a read of this if you haven't already

Also regarding rescaling load axis use this tool

 

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In regards to the sprint MBT tables, reason for asking whether being able to use them or stick with the stock ones is that the sprint uses the same engine as the xr6t, but with the f6 turbo, so essentially if running a turbo similar size to that of a gt3582 with the same compression ratio of the engine, would it be more accurate?

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