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Compare tables - Speed Density vs Alpha-N

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Is there a simple way to compare tables for a Speed Density setup and understand how they would be configured if it were Alpha-N?

As a newbie, I am constantly reading articles and comments but most are for Speed Density systems. I am running ITB's and therefore, an Alpha-N system.

I know they don't directly interchange, but are there some generalizations that I can use?

Example. In developing an AFR target table, the speed density system shows a lambda of 1.0 at all rpm up to 75Kpa. What would a similar setting be on a TPS system? MAP is a little more linear than TPS, especially with ITB's. The TPS line is much more curved, flattening after about 70% open.

I know you can't directly cross-over. But it would be helpful to understand some percentages maybe, to help learn how it would relate to the other type


Hi Paul, I'm doing ITBs on a cammed GM LS3 and the attached shows you my Alpha-N approach. At low RPM small throttle angles will give the engine most of the air it can use so AFR targets and commanded spark reflect that it is making most of the available torque at as little as 15-20% TPS. By 3k rpm its much more like a normal speed density table. Note I have used a non-linear TPS axis to try and reflect the relationship between throttle angle and flow and give good resolution down low where small changes have a big effect on flow. Cheers, Andrew

Attached Files


Thanks for the comments. I have done the same on mine. This is one of my older Target tables. I've dedicated have the Y axis to below 30% to get the resolution and control caused by the non-linear airflow with the ITBs. It works well

I was kind of looking for a generalization that we can use when looking at a Speed Density based table. Do you feel the pressure reading is relatively linear and if we were to flatten the air input/Tps angle curve that it would cross-over a little better? Looking for someway to read the other guys table apply the logic to our systems.


Attached Files

Hi Paul, this is as scientific as I get - my "method" attached! Datalogging is required to fine tune. This is for 50mm TBs on a 6.2 litre engine. Cheers, Andrew

Attached Files

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