Quote:
Originally Posted by Lapkritis
The OEM FPR with vacuum reference is rising rate. Your statement again, factually incorrect. AGAIN.
|
Actually no. It's actually
rising pressure to maintain a fixed pressure-differential between the injector-inlet and tip. Rate is the 1st derivative of pressure similar to distance, speed and acceleration. We have fuel-volume, pressure and rate-of-change.
volume = pressure * area * time
pressure1 = base pressure + (manifold pressure * 1) ; factory
pressure2 = base pressure + (manifold pressure * increasing-rate)
The factory FPR adjusts the fuel-pressure directly in relation to manifold-pressure to maintain a constant 2.5-bar pressure-differential between the fuel-injectors inlet & outlet. Under manifold-vacuum, it lowers the fuel-pressure (since fuel is now being sucked out of the injector). Under boost, it increases the fuel-pressure to counteract the increased manifold pressure to yield the same 2.5bar pressure-differential across the injectors. This allows for easy pulse-width calculations given any amount of air-flow. With 2x the air-flow, it's simple to just double the pulse-width in the tables. It's so simple in fact, that the 951's DME doesn't even know or care about boost. It's basically the same box as the 944na and simply has modified programming for more air-flow and larger injectors.
A rising-rate FPR increases fuel-pressure
faster than increase in manifold-pressure. This was an old-geezer method of tuning by adjusting fuel-pressure. In and of itself, it doesn't pose any issues if the rising-rate is incorporated into the chip-maps. You'll have to go through the entire chip-map and reduce pulse-widths to account for the extra fuel-pressure over stock. However, on a system that allows customized chip-programming, it's much, much easier to assume a constant pressure-differential across the injectors. Especially with a system like Rogue's that allows for mapping based upon MAP and can differentiate between partial-throttle boost-conditions such as 10psi vs. 15psi.