Originally Posted by ibjamin
But the system really shouldn't use a FMU should it? I would think that you want a steady fuel pressure and then just adjust the maps to get the fueling right. Isn't that correct? I thought an FMU was just a crutch to allow you to put a SC on a car and be able to use the stock computer program. Shouldn't a custom tune remove the need for an FMU?
Once you start getting into a SD tune, then yes you just adjust the maps to add more fuel. The problem is, the stock operating system isn't setup for boost. The VE table only measures up to 105kPa. A FI car will require a 2-bar MAP sensor and custom operating system to tune that way - not to mention a great deal of time (and possibly a speeding ticket or two) to tune it trying to hit most of the cells.
As for the FMU, I know guys in the FI section are running systems that add extra fuel for every extra pound of boost. This is one way to help dial in WOT. Don't close your mind to tuning it the old way by manipulating the IFR and PE tables. This works fairly well even though it's kinda frowned upon here. A local guy here just tuned a Mustang w/ twin turbos that way in a day or two. The car made 620+ rwhp & 650+ rwtq and made the drive back to Colorado getting 25mpg with 72lb injectors. This is also how my current car (not in sig) is tuned (was done by a shop in PA). It puts down nearly 430rwhp and gets 27mpg on the highway when I keep my foot out of it.