Here’s a more technical rant that deals with fuel delivery. Anyone with over 500rwhp should seriously consider replacing the stock Fuel Pressure Regulator with a MAP-referenced one (even if you have triple pumps). Here’s the technical description why.
Using the stock Chrysler fuel returnless system, the pressure in the fuel lines is maintained at 58-60psi. However, fuel line pressure actually means nothing for the PCM fuel calculations. What really matters is called Delta Pressure. Delta Pressure = Fuel Rail Pressure + Manifold Vacuum. During idle, there is a lot of vacuum in the manifold which helps pull the fuel through the injectors. Let’s say your base fuel pressure is 58psi. If you have 20 inHg vacuum in your manifold (~10psi), it’s actually like your fuel pressure is 68psi! 68psi is your Delta Pressure.
Anyways, my point. When you’re working with a vehicle that has boost, the opposite happens to your Delta Pressure; it goes DOWN. With a Techco base kit, you only have ~6psi boost so you can get away with the lowered Delta Pressure… barely. When you’re 10+ psi (higher boost), you REALLY start to lower your Delta Pressure which really kills the amount of fuel you can get through the injectors. Example: Let’s say you’re using the stock Chrysler fuel system with 14 psi boost. Your RAIL pressure may be a constant 58psi (which you can see on your fuel pressure gauge) but your delta pressure is only 44psi! Normally, the G302 injectors flow ~60 lb/hr @ 58psi Fuel Pressure. When you introduce 14psi boost, those same G302 injectors only flow ~51 lb/hr @ 58psi Fuel Pressure.
What a MAP-referenced FPR does is instantaneously adjust the Rail Fuel Pressure by the same amount of vacuum or boost in the manifold. The stock Chrysler system is “Constant Rail Pressure.” With a MAP-referenced FPR, it’s a “Constant Delta Pressure” system (the rail pressure fluctuates to maintain a constant delta pressure instead of the other way around. It’s almost a requirement for any higher boosting engines.
Another reason why I usually switch almost all higher boost customers over is because I come from a more formal calibration background where all the calibration data is accurate and correct instead of falsely specifying calibration data to make the car act like you want.
Lastly, DiabloSport does not have complete control over something called “Fuel Correction vs MAP” so instead of calibrating data correctly in the boosted region, either the VE table or injector transfer functions have to be falsely set in order to maintain the correct A/F ratio. When you switch the car to a Constant Delta Pressure system, there is no need for the “Fuel Correction vs MAP” table so this table is set completely to 1.0 and all the correct calibration data can be set in both fuel injector and VE calibration.
An example MAP-Referenced Adjustable Fuel Pressure Regulator can be found here:Aeromotive A1000 Injected Bypass Regulator (opens in new window)
Related Post…
Example Fuel System Setup for High Horsepower Hemi engines (opens in new window)