Gen 7 ?
Melting Slicks
Joined: Jun 1999
Posts: 2,872
Likes: 3
From: Wilmington NC
that is giving the ecm a smaller window to work with hitting your target Air fuel ratio.. it is telling the computer how efficiently the engine is ingesting air at the given RPM and vacuum range. if the engine was 100% volumetrically efficient it would be ingesting 355/8 or 43.75 cubic inches of air which would be completely filling the cylinder at bottom dewad center to its maximum volume at std atmospheric pressure.. meaning it sealed with no pressure differential. this amount of air is then calculated by the ecm and the appropriate amount of fuel is added to achieve the target air fuel ratio in your target AFR Vs MAP tables. being the engine becomes more volumetrically efficient closer to Zero vacuum (usually on average .850 or 85%VE for a high performance engine with good heads and appropriate camshaft) the number will increase as rpm increases and manifold vacuum decreases.
now the kicker.. above atmospheric conditions ie.. boost the engine becomes greater then 100% volumetrically efficient. this however is computed by the ecm by analyzing the manifold pressure in positive numbers or boost.. so you do not need to go above 1.00 unless fueling becomes too lean. so a quick break down.. from idle, your VE values should be closer to .300-.450 and as rpm increases you should increase the ve values closer to .850 once in boost as some have discovered you may be closer to the .950 range. use the autocalc function in the base VE table under fueling while idling.. if it stays pretty consistently in a 4 cell square range you can put those value close to each other or even the same to keep the engine from surging or rapidly changing the fueling strategy. the auto calc is basically calculating the read air fuel ratio from the wide band O2 sensor, the amount of fuel it put in through the injector pulsewidth and the value used in the ve table and it calculates the new VE value. by hitting autocalc here it will plug the calculated ve value in that cell and it should be much closer to the tru VE at that vacuum rpm range. follow?
Chris
now the kicker.. above atmospheric conditions ie.. boost the engine becomes greater then 100% volumetrically efficient. this however is computed by the ecm by analyzing the manifold pressure in positive numbers or boost.. so you do not need to go above 1.00 unless fueling becomes too lean. so a quick break down.. from idle, your VE values should be closer to .300-.450 and as rpm increases you should increase the ve values closer to .850 once in boost as some have discovered you may be closer to the .950 range. use the autocalc function in the base VE table under fueling while idling.. if it stays pretty consistently in a 4 cell square range you can put those value close to each other or even the same to keep the engine from surging or rapidly changing the fueling strategy. the auto calc is basically calculating the read air fuel ratio from the wide band O2 sensor, the amount of fuel it put in through the injector pulsewidth and the value used in the ve table and it calculates the new VE value. by hitting autocalc here it will plug the calculated ve value in that cell and it should be much closer to the tru VE at that vacuum rpm range. follow?
Chris
