Six_Shooter's "little" project v.240z

[Dylan]

I just googled it and now my head hurts.

[Holden202T]

Less exhaust back pressure

[VL400]

Less exhaust back pressure

If baro is say 80kPa when WOT and seeing only 80kPa the fuel requirements are the same amount as when it was showing 100kPa WOT and baro at sea level.

[Holden202T]

I read all the helicopter thread

[Six_Shooter]

Am pretty late to the party but I think the VE table needs to be explained as its being well and truly confused when boost is thrown in to the mix. My comment earlier meant what it read - you will not see double the VE going from 90kPa to 180kPa, it will only increase a small amount.

VE is volumetric efficiency, it is a VOLUME ratio that defines how efficient the engine can pump air. Compressed air is air that is more dense, it has more mass for a given volume. The engine pumps a volume of air in on the intake cycle, if the air is compressed to 100PSI or your at the top of Everest it still pumps a volume of air in. It does not begin to pump double the volume of air when changing the pressure from 100kPa to 200kPa. But, when you compress the air you can get more mass in the cyl for the same volume. This is why the ECU needs to know the MAP pressure, its calculation is all about injecting X parts of fuel mass for Y parts of air mass. So the boost multiplier is the fuel PW multiplier to compensate for the more dense air and ensure the ECU can still maintain the correct fuel/air ratio. You then use the boost VE table to define the engines VE at each load point just like you do in the 20-100kPa region.

The tables that delcowizzid posted are exactly as you would expect, around 15% or so better after efficiency after feeding in some boost. If designed/setup well the engine will operate more efficiently but certainly wont go anywhere near double the 100kPa values. If you see a VE table that goes from 100 to 200% under boost the ECU is setup differently and not strictly correct.

And while we are on the VE subject, why does VE go up when operating at higher altitudes with lower air density?

:facepalm:

I know, I said earlier I understand how or what VE is. You seem to be under the impression that I think it will somehow double for some reason...

I have no idea where you got that impression from.

There is just confliction information how the VE tables should be set-up. The tuning guide suggests that the boost VE should have a curve to it as more boost is applied, which makes sense.

The kinjflow calculator seems to be based on a naturally aspirated engine, that will set maximum VE in the table at or near 100% VER, this will leave no headroom in the boost table to increase it at all. Then there's the boost multiplier table, which really is self explanatory. It seems that the way that most people are using that boost VE table makes it a pointless table to have. The boost multiplier table could look at the 100 KPA column and still fuel the engine EXACTLY the same. There seem to be at least a couple people using the table with a curve as shown in this and a couple other threads.

This is where I thought I would use effective displacement at a certain boost pressure to find a different kinjflow number that would allow a curve to happen in the boost VE table, and reduce the maximum VE in the 20 to 100 KPA table, that could carry over to the boost VE table.