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Kpa or psi for load axis

General Tuning Discussion

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it seems like kpa is the most common for a load axis on the majority of ecu's I see people using. But in mine particular (aem v2) it does give you the option to choose between kpa and psi. I had my car tuned a few years ago before I had a single understanding of tuning and my tuner tuned it with The load axis reading in psi. Now is this just a personal preference or is tuning with the load axis in kpa better, as this seems to be the most common.

I prefer kpa. 100 kpa = 100% air at sea level. 50 kpa = 50% air in the intake compared to sea level. The math just works easier.

Really? To me it just seems easier to look at the load axis and see 10psi, and know that is 10 pounds of boost instead of 171 kpa equaling the same amount of boost. So it's really a preference?

It really is a personal preference. I prefer to work in kpa myself as I've grown up with the metric system but as a professional tuner you really need to be able to work in either unit and convert back and forth between them in your head. Fortunately most ECUs give you the option to easily switch between units with no impact on the actual tuning.

Awesome! Thanks for the reply guys!

The nice thing about using kPa absolute is that it makes interpolation much easier when you are building maps. You can have nice even steps of 500rpm and 10 kPa for example, so that your spark tables are behaving more predictably.