After modifying an engine for more power it's necessary to increase the capacity of the fuel system: usually bigger injectors and a bigger (or additional) fuel pump.

What is the real purpose of more pumping capacity? More flow? Or more flow AND more pressure?

I'm asking because I just had to remove a damaged fuel pump supplied with a Vortech supercharger kit. This pump is supposed to be installed in series after the stock pump located in the fuel tank.

With only the stock pump the fuel trims are now around 2% leaner than before (I was surprised to see only that little difference), so I have to assume that the purpose of the additional pump was just to ensure enough flow but not necessary more pressure. Am I right?

This is a 98 Trans Am, the injectors are Bosch 36 Lbs/h.
There isn't a real pressure regulator, just an orifice in the return of the fuel line.

The supercharger is no longer installed and the car is tuned for NA.


Thanks

Stefano

You have to work backwards as to what you want as the end results and what existing parts make up the TOTAL fuel delivery system and the requirements the powertrain needs to function with little engine knock and also to use fuel to cool pistons and if need be the CATs.

The weakest line in the fuel system dictates the total fuel performance.

Many people do it the cheap way by adding an external pump in series with the internal tank pump which still leaves the delimiting factor is the internal pumps ability.

Adding higher pressure is really a cheap way to force the injectors to flow more volume but the injector still does not function well when it goes static or about a 80% duty cycle.

Some add higher pressure and also allows more volume flow but forget the stock fuel lines then are too small and preventing more flow.
Same can be that the fuel rail itself can be too small when more volume is required.

The correct path is to determine first what the powertrain requires in all engine conditions, weather, type of gas grade forced to use ( such as E10) and type of driving.

Then determine all the parts and which ones would not fit within the fuel goals and the new parts being added thus a pump alone may not be the total design path.

Best case is if adding any type of boost lets say adding another 100 flywheel HP to install a higher flowing internal pump, determine if it's current draw requires a larger gauge wiring, increasing the fuel hose diameter and then the proper fuel injector so that it will not peak over 80% duty cycle.

If needed add a larger diameter fuel rail and if the car has the older fuel return vent system that a adjustable fuel regular replaces the stock adjuster.

Also determine if the fuel damper is a delimiter factor but in the end as to pump, you want more flow volume instead of increasing just the pressure to force injectors to flow more.

Is there an optimal pressure for a fuel injector? Or just a minimal pressure?
Does the pressure change the spray pattern or the dimension of the droplets?

Fuel regulator itself can careless what the pressure is.
They are vaccum controlled thus any leaks can effect how fuel regulator functions.

Yes of course as the pressure changes in regulator effects injector pressure and flow pattern

What is the result of a higher / lower fuel pressure?
Sure, the spray pattern is different, but what is the relationship between pressure - fuel consumption - engine cooling - valves cooling - ...?

I saw your post about programming the correct Injectors offset voltage and I can imagine that fuel pressure has a similar rule

Stefano

Well that can depend on the type and design of the injectors.
Some just do not spray well when flowing more, esp at higher injector pulse widths.

If we look at GM's history they were one of the 1st to go from 43 PSI rail pressure to 60 and GM has better fuel mileage then other makes with the same amount of engine output.