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AFR Target Map (technical question)

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Hey all!

question on the AFR target map...

what is the "LOAD" measuring in kPa? the pressure of air going into the intake manifold?

If so, then how can one have theoretically 300 kPa of air coming into the manifold with relatively zero RPM? Is someone hooking up a shop vac a focefully blowing air into the engine or something? I guess, I can't make the disconnect between pressing the throttle (i.e. RPM) and the "LOAD" of the AFR target map?

Better stated; if I hold the throttle to 1000RPM; how do I change the LOAD of the engine in the AFR Target Map?

Attached Files

They wouldn't, but maps are made by columns and rows, so there will be unused cells (like shown in your attached picture) just by the nature of how an engine actually runs and the cells it will actually use.

yes kPa is air pressure in the intake manifold.

There will be some corners of the map that are just rarely or never used. For a different example say you had a turbo can that has a 7 psi spring in its wastegate that spools at roughly 4000 rpm, the area in the map above 4000 rpm that's below 7 psi of boost will also never be used. Unless of course a mechanical failure occurs causing you to lose boost pressure. Andre explains in the course you can extrapolate the data you have to fill those "un-tunable" areas of the map. They won't be 100% accurate but it'll at least still run if it ever touched those areas.

A braked dyno can be used in steady state to help get to some of those areas. You can tell the dyno to hold a speed and it will hold the engine's rpm and apply more braking force to apply load onto the engine.

The term "Load" is used for indicating the percentage of air mass entering the cylinder under different circumstances compared to the mass of air that would occupy the same volume of cylinder under normal conditions (0 degrees Celsius, 0 humidity, 1 atmospheric bar of pressure) which is 100 percent Load.

For example, if your cylinder with its fixed volume gets 10 grams of air under normal conditions and when it's boosted it gets 24 grams of air at 7000 RPM the acual Load is 240 percent so you would go to your map and find the cell that corresponds to 240 and 7000 rpm ( picture is attached).

And it also works backwards - if the same cylinder gets only 5 grams of air at 3000 RPM the actual Load is 50 percent.

Calling intake manifold pressure the Load isn't technically correct to me as it doesn't tell you how much air actually gets inside the combustion chamber since engine VE is always changing...

Attached Files
  • Screenshot_20231120_025758_cn.wps.moffice_eng.jpg
  • Attachments may only be downloaded by paid Gold members. Read more about becoming a Gold member here.

It seems you have fundamental mis-understandings of what pressure and flow are, and possibly how they're measured?

If you do a little revision on those, it should all become clear.

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