So...now I'm trying to learn more about all this, and I find the following at a link I Googled:

Problem with just adding larger injectors: The higher the fuel pressure, the harder the fuel pump has to work, and more electrical energy is required to open the fuel injectors.

What can go wrong with larger fuel injector upgrades? I often see builds with goals of 500hp and more using 1000cc fuel injectors because of the price jump to a larger injector. They assume they can simply turn the fuel pressure up to increase the flow of the injectors if they run out. While it may be true that 1000cc injectors flow over 1500cc at 100psi base pressure, it is simply not feasible to run that high of a base pressure on a regularly driven vehicle. Remember that a 100psi base pressure is 120psi at 20psi of boost.

At these high pressures, fuel flow is actually reduced in the rest of the fuel system. The resistance to flow in the fuel lines increases as the pressure increases, restricting flow.

Fuel pumps are rated at 43psi of pressure. Your 320lph fuel pump only flows 200lph at 100psi. Most in-tank fuel pumps have a built-in pressure relief valves that open at 100psi, making it impossible for fuel pressure to raise with boost using a 100psi base pressure. Even using a base pressure of 60psi will put serious strain on the fuel pump, causing potentially lean conditions and premature pump failures.

This invites the question...will a larger injector flow correctly at conservative supercharger pressures?

Not sure I am following you... can you clarify your question?

I don't think anyone here is cranking up their fuel pressure to add more fuel... I think most people stick with the OEM ~52psi and just upsize their pump and injectors. With a return setup and boost referenced regulator you could easily see 60+psi of actual fuel pressure at full boost with a modest setup, but the base pressure is still much lower in the 50's. Even the lower pressure model of the Walbro 450 has a working pressure into the 80's which would allow you to run 30psi of boost and still keep proper fuel pressure.

edit: I think I see what you are asking now... that link might be geared towards fuel systems with very few injectors... It's misleading to say "Its a bad idea to try to have 500hp with 1000cc injectors" without specifying if they mean 2 injectors or 200 injectors. 6 1000cc injectors is EASILY capable of 500whp on pump or E85. I ran out of injector at 538whp with only 600cc injectors on pump, and I am only running the stock 52psi regulator with no boost reference at all.

The problem I'm having now is that apparently the recommendation is not to upgrade the fuel system for a basic A2A system...but Topz says to upgrade the pump. Then, apparently there is a recommended adjustment (?) to the tophat (?). And finally, an idea is being floated to upgrade injectors with no other upgrades, if I am understanding correctly. Can a larger injector manage the same spray pattern as a lower-flowing stock injector at the same pressure? Could a larger injector cause driveability issues at lower RPMs? Will a stock injector deliver enough fuel at 6-7k and 9psi?

I can see where it can get a little confusing... I'll try to address it in pieces (at least the pieces I can help you with!).

Fuel system - CJM's answer to cupcakez was in reference to converting to a return fuel system. For his build he was only saying a return fuel system was not completely necessary. This is separate from upgrading the pump and injectors.

Pump and Injectors - you absolutely need to upgrade these when going FI. I am running a Walbro 255 and 600cc injectors, and I am pretty well maxed out. Wish I had gone a little bit bigger. If you want E85, you definitely need to go bigger.

Top Hat - the flimsy top hat on the stock fuel pump assembly tends to break where the rods are held in place. CJM makes an aluminum top hat to replace it.

idea is being floated to upgrade injectors with no other upgrades, if I am understanding correctly - you are not understanding correctly. You definitely need a pump and injector upgrade at a minimum.. for a modest 500whp build that is probably all you need. I think people are referring to upgrading injectors on top of the 255lph pump that Stillen provides with their kit.

spray pattern/driveability at low rpm - I do not know enough about the technical aspects of fuel injectors to talk about spray patterns.. but in the past this used to be a bigger problem (and by past, I mean like 1997). The stock ECU + Ecutek/Uprev is a powerful, highly granular tuning solution these days and high quality injectors and a good tuner should get you straight unless you are running gigantic injectors.

Will a stock injector deliver enough fuel at 6-7k and 9psi? - absolutely not. Upgrade the pump and injectors. I would recommend an Aeromotive 340 (as it is easier to install than a Walbro 450 because of the physical dimensions of the unit) and 750cc+ injectors... if you ever THINK you might go E85 you may as well just jump up to the ID1050x and Walbro 450. The price difference between difference sizes is not that much... I think the Walbro is actually cheaper than the Aeromotive in the pump department. Should you decide to go E85 later, you can reuse those components and upgrade to a return fuel system.

Does that help?

You're awesome! Thank you! :hello: