The statements about using the FPR to increase fuel delivery are quite accurate. The MPi injection system is maxed out at the 76-85 hp level. Tolerances and production variances probably explain why some kit installations yield 75hp and other installations of the same parts give 80+.
I'm pretty sure the original Cooper "90hp" ("S") kits for the MPi back in the 90's used a fuel pressure regulator that was crushed (yes, squeezed with pliers or other crimping device) to crudely raise the fuel pressure, thus supplying extra fuel to support higher airflow. Even if this gives a predictable increase in pressure, the drawback is that it may well overfuel at lower speeds.
As recounted above, the MPi is not a mass-air injection system that measures the amount of air coming in to the engine. It's a speed-density meterless system that estimates the amount of air based on the physical characteristics of the intake system, the barometric pressure, and the air intake temperature. In theory, the lambda sensor should detect that the air/fuel mixture is over-rich at lower speeds and reduce injector flow, but I've been told this doesn't really work that well in practice and the result is abysmal fuel economy.
So a rising-rate FPR should in theory deliver extra fuel pressure when needed. The trick is to get one that increases fuel pressure as vacuum increases, which is what a normally aspirated (non-boosted) engine needs. Most FPRs increase fuel rate with boost pressure, which doesn't do much for non-boosted application.
(I wish the prototype ECU he mentions in that old article had actually reached production, but I haven't heard anything about it in at least 7 years.)
Edited by bluedragon, 24 July 2018 - 12:54 AM.