Volumetric Efficiency Bank 1

From SCT SRT Wiki

Under Section: Speed Density

Name: Volumetric Efficiency Bank 1 (VE Table)

Description:

The Volumetric Efficiency Bank 1 table describes the "breathing" ability of the car through it's entire range of funtion. This table should only be altered when the actual volumetric efficiency of the motor has been changed. A few things that can change the VE of a motor are cams, port work, different turbo, compression ratio, etc. Volumetric efficiency is a ratio of the amount of air and fuel the engine is actually taking in compared to the amount of air and fuel the car could take in at that pressure ratio.

Example: At a pressure ratio of 1.0, the car SHOULD be able to injest 2.4 liters of air every 2 revolutions(4 combustion events). In reality, it MAY be injesting only 2.25 liters. 2.25/2.4 gives us .9375. This number is a ratio and has no unit of measurement.

Use:

This table is used for the calculation of fuel in ANY and ALL driving conditions. It should not be used to increase/decrease fuel during WOT.

Usage Tips:

If you increase the numbers in the table, you are essentially adding fuel and vise vera, by making the number smaller you are taking fuel out.

RPM is pretty obvious.

The pressure ratio is the ratio of pressure between absolute manifold pressure and atmospheric pressure. These are absolute values so if you're reading relative manifold pressure (what a normal boost gauge would read) you need to calculate absolute pressure. I just suggest that you do all your calculations based on the factory MAP sensor readings for accuracy and simplicity as these values are already absolute. You can obtain atmospheric pressure by turning the ignition on (but not starting the vehicle) and reading the PSI indicated from the MAP sensor. Here's an example for you... Lets say at 2300 RPM and 11.3 PSI of absolute manifold pressure your long term fuel trim is -24%. We need to find the pressure ratio now. So find the atmospheric pressure and make note of it (for simplicity sake lets say were at sea level and the pressure is 14.7 PSI). Now we have everything we need to calculate the pressure ratio. So, being that our absolute manifold pressure is 11.3 PSI (which is below atmospheric pressure) we know that our pressure ratio will be less than 1.00 (the manifold is under vacuum). Now we simply need to take our manifold pressure and divide it by atmospheric pressure. In other words, 11.3 PSI / 14.7 PSI = 0.77. So our pressure ratio is 0.77. Now we start making small adjustments to the VE table as close to 2300 RPM and 0.77 pressure ratio as possible until the fuel trims come into check.

Related Tables:

PDF File with Atmospheric Pressure Ratios: Media:Atmospheric Pressure.pdf

Screenshot: This is for a stock map