over lay
Up to Engine Tuning
Hi Nick,
An overlay fuel table is referred to in Link as a 4D, 5D, or 6D table depending on how many dimensions are needed.
A normal fuel table uses RPM on the x axis, and load (MAP or TPS) on the y axis.
A situation where you would use a 4D table would be where the engine has multiple throttle butterflies and has trouble making reliable consistent vacuum at low load levels. The normal 3D fuel map would use the TPS and RPM as the axis, and all low load tuning would be done on this. Once the point where a consistent vacuum is reached, the tuning would progressively move from the 3D fuel table to the 4D (overlay) of MAP and RPM.
The PCLink help file has quite a good explanation if you want to read more. Search the index for the '4D fuel table' section.
The majority of engines out there do not require overlay tables. They are more often used as in the example in PCLink (with NOS).
Cheers,
Scott.
