[Cobrat24]

Originally Posted by olddog

Be warned that Ford started with Speed Density. It uses a MAP sensor in the manifold to estimate what the air flow into the engine is at a given throttle position. It does not work well with big cams, as the vacuum can be lower at idle than it is at off idle with such a cam. Second it does not automatically adjust for altitude changes. When you turn the key on the ECU saves the MAP sensor reading and assumes that is the atmospheric pressure. It does not update again until you turn the engine off and restart. So if you drive 4000 feet up a mountain, its no better than a carb, however turning the engine off/on is much easier than changing jets.

Then Ford went to Mass Flow to truly measure the mass of the air entering the engine. It handle big cams much better than speed density, and you can start at sea level and drive to 12000 feet with perfect AFR. Now there are issues with big cams, but that is another long story on what is needed to compensate.

Most after market system are speed density with an option to go to alpha N. Alpha N uses throttle position only and is more crude than speed density. These systems can be tuned to run well, but they will not automatically compensate for elevation change.

Someone mention Pro M. Pro M used to be MassFlow. MassFlow used a 1989-1993 Mustang A9L ECU. I have one on my Cobra. It is a decent system, but in my opinion some of the claims were BS. Before going to a quarter horse chip from Moats and software to tune it myself, I looked hard at the new Pro M. It looks like a great system to me, but I did not buy it. I would have had to replace too much and spend to much $$ to switch over to it. If I remember correctly the cost of a complete system (fuel pump to intake, inclusive - wire harness and distributor) is ~$3500 give or take. I would look hard at that.

Much appreciated on the FI information. My cobra has the ford ecu with wiring in the car even though I'm carb'd. I need to get under the passenger side and see what I have and how much is there. Thinking of possibly utilizing the oem stuff with after market intake. I am very aware of the aggressive cam/vacuum issue with FI. Looking into options on that as well.