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ve table question.

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How can some cells on a ve table be over 100? I don't quite understand.

That would be when a motor is in boost. If it's not rich and right where it needs to be, it's usually in boosted areas. Either that or the N/A motor is built extremely efficient. In Nascar, the motors are built so efficient that in a certain part of the powerband it acts like its in boost. it's called the supercharger effect.

Are the numbers on the VE table in form of percentages? If so how can an engine have over 100% volumetric efficiency if 100% is the maximum efficiency an engine can have ?

It's the relative efficiency compared to the displacement of the engine. So, if the wave pulses can pack more than 100% of the engine displacement worth of air per cycle, then the VE is greater than 100%. A well-designed header and tuned intake can achieve this.

Here's a book with a lot of the science behind designing such an exhaust system:


So another thing I don’t understand is when tuners make adjustments to the VE table what exactly are you changing? I understand fuel tables and spark it’s just the VE table that is very confusing to me.

If you changes the numbers in the VE table in simplest terms as I can think of, you’re saying more or less air is entering the combustion chambers. So this intern does it’s calculations and adds or subtracts fuel. Engines can get over 100% volumetric efficiency. This is like David said either through a properly design intake, intake manifold, heads, and exhaust system, as well as cam design. Or through a form of forced induction like a turbocharger or supercharger. Because positive pressure is boost in FI application. So if you hear someone say that I’m running 10 psi of boost, this means that 10 psi more air is being compressed and “forced” into the cylinders, hence forced induction. You have atmospheric pressure entering the engine at 0 (on a boost gauge) and anything over that is positive pressure. Or anything over 100kpa (in the VE) is positive boost pressures.

EFI systems with VE-base tuning, count on the VE table to describe how much of the available mass of air is used by the engine each time the cylinder is filled. The mass of air can be calculated using the pressure (manifold pressure) and temperature of the air. Then using the target Lambda (or Air-Fuel Ratio), the EFI system calculates the mass of fuel required, and using details about the injectors, determines how long to open each injector.

To tune the VE table, we simply adjust the VE number until the target Lambda/AFR is achieved. If the current mixture is reading too lean, increasing the VE value will increase the amount of fuel that will be delivered, and thus change the mixture.

Some ECU are configured with Mass Air Flow sensors (MAF). This directly reads the mass of air that is passing into the engine. Once properly calibrated (using a similar method -- adjusting the MAF transfer function until the measured Lambda/AFR matches the target Lambda/AFR), then this handles the change in VE at different operating conditions, without requiring a VE table.

Thanks so much guys.

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