JonathanD

I was doing a little research and have stumbled across something a little troubling and contrary to what I've heard from all Audi tuners. I found the formula that goes with injector flow rate and horsepower. I believe that it is Brake Specific Fuel Consumption (BSFC) = mass flow rate of fuel/engine power. RC Engineering found that stock A4 injectors flow at 244 cc/min at 50 psi and 255 cc/min at 55 psi at 80% duty cycle. This is good for only 165hp at a BSFC of .55. According to this you can't make any more power without increasing the fuel pressure past 55 psi. So how are all the tuners claiming near 200hp with only a chip upgrade. Wouldn't the stock injectors prevent that? It doesn't seem like it matters what you tell the computer if the injectors physically can't do what is necessary. I don't know any way to explain this away. I understand that you can get much better increases in torque, which will make the car feel faster (quicker) than more horsepower alone would anyway, but as for actual horsepower numbers...some one explain this to me. Or is this just the way it must be? I've driven an AMS chipped car and was very impressed, but it could easily have been a large increase in torque that i was feeling. Can't say that I'm complaining, just curious.

Audiboy

Typical stock fuel pumps are built to pump in excess of 100 psi (of course at the sacrifice of flow rate). A fuel regulator on a typical car controls the pressure from 22 psi (idle) to about 35 psi (WOT). I am surprised to hear 55 psi as that sounds a bit too high because the injectors could freeze (close or open) as the electrical solenoid doesn't have that much force to handle the pressure - I'll need to read more on this. But anyway, for the 1.8T at least, the chip controls the adjustable fuel pressure regulator, the boost valve and of course the injector duty cycle and more. So I wouldn't doubt a 220+ hp setting with just a chip alone. Any higher, you will need larger injectors and a different duty cycle setting (so the car won't flood) to utilize the lower PSI, otherwise, upgrade the fuel pump, or dump the whole fuel system and use alcohol :-) (CH3OH) & (C2H5OH)<p>

Brett

The ECU has no control over the fuel pressure. The injectors will not freeze at 55psi. Stock injectors will not flow 220HP, at least not at an acceptable air/fuel ratio. <p>Brett

DaveN

My old 87 controls the fuel pressure, I don't know that the A4 does, haven't looked to see it has the same type of valve, but I'm also unsure how you would make the fuel injection work without some type of pressure regulation.

Tony

The fuel pressure regulator maintains a constant differential pressure across the fuel injector (fuel absolute pressure minus manifold absolute pressure. Some older K-Jetronic (CIS) systems (Audi 5000 Turbo) used the manifold pressure to richen the m