[olddog]

Well I'm no expert and don't have much experience working on EFI, but I have read a fair amount and have tried to learn more. There are some things that were said that could be true and could be false depending on the type of EFI system.

The early EFI systems were speed density. They use manifold vacuum (MAP) to estimate the amount of air flowing into the engine. They can be very accurate, but they cannot work with a radical cam where the manifold vacuum is very low at idle and increases a bit as the rpms go up.

A Mass Air Flow system measures the amount of air entering the engine directly, so manifold vacuum does not bother it. It is the easiest to tune because a direct measurement is easier to work with, however when the cam is so radical that air is pulsating back and forth past the MAF meter it falls down, too.

Some aftermarket systems you can select speed density, MAF, or Alpha N. Alpha N uses only throttle position and RPM to estimate air flow into the engine. It can handle the nasty cams, but it is less accurate and requires a lot more skill and knowledge to work with it.

The stack injections systems I have read about do not use MAF. They tie all the ports together under the intake to get a vacuum MAP reading for speed density or go Alpha-N.

You need to ask the right questions before you buy one, if you plan to do it yourself. Or you need to find someone who the manufacturer recommends or certifies to install and tune if for you.

There are a lot of claimed systems that tune them selves. Most work to some degree or another (not all). Most leave something on the table, Hp, mpg, emissions, drive-ability, etc.