Originally Posted By: George7941
Every one of the replies skirted my question.
1) The actual displacement really does not matter, whether it is 4.25l or 4.34l. 4.3 is the figure used in my calculations and in the OTC app, so it is the exact same figure in both.
2)Pumping losses would explain why the efficiency is less than 100%, but that was not my question. All I am doing is questioning the discrepancy between my figures and the app's. Ditto "sweet spot", "supercharging" etc.
3) The air temp and Maf are the values reported by a scantool, but, again, all immaterial to my question.
WHY IS THERE A DISCREPANCY BETWEEN MY FIGURES AND THE OTC APP?
Hard to say how they are calculating VE in their on-line calculator. The VE is simply the ratio of how much air the engine actually takes in vs. how much it could 100% ideally take in based on displacement. Pumping losses and intake/exhaust restriction are what makes VE less than 100% and should already be taken into account when using intake mass flow (g/s) and intake air temp vs. what the 100% ideal intake based on displacement could be.
Seems it should match your numbers better as it should be a pretty simple calculation as you've shown. Maybe they have an error in their calculation model, or their are accounting for something not obvious.
You should email them and show them the issue to see if they look into it and respond why the discrepancy.
Email:
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