GIGAPUNK

iTrader: (2)

I bought a set of Delphi #50 injectors matched by racetronix.
Part Number 17113738 (OE # 17104487)
Static Flow Rate: 50.0 lb/hr @ 43.5PSI (300kPa) 525cc/min or 6.4gm/sec
Static Flow Rate: 57.7 lb/hr @ 58.0PSI (400kPa) 606cc/min or 7.4gm/sec

Ball/Seat Design with 6-Hole Diffuser Disc

I have been trying to figure out what would be the ideal fuel pressure to run with them. I'm building a naturally aspirated L92 and have a walbro 255HP pump.

I have calculated that I can run any where form 40 to over 70 psi without maxing out either the injectors or the pump at my projected horsepower levels. I have a SX fuel pressure regulator, and plan on doing the tuning myself

Also, what about using the vacuum reference to get an even lower fuel pressure at idle? Will that make it easier or harder to tune?

My question: is there anything to be gained by using a lower or higher fuel pressure? Some tuners have told me that with large injectors you should use a lower fuel pressure to increase resolution at lower rpm, there by giving me a better idle. While others reccomend to use a higher fuel pressure to get "better atomization" and possibly higher efficiency.

SSpdDmon

iTrader: (10)

I'd say run 'em at 4-bar since that's what these motors were designed around from the factory. You can adjust idle characteristics in the PCM. A car with that kind of setup could really benefit from a custom operating system, which would also help to ease idle tuning.

GIGAPUNK

iTrader: (2)

The factory setting of 4 bar doesn't really affect me because I'm running a totally aftermarket fuel system. But, I realize that when I'm getting started and trying to use base tunes off the net that being factory will give me more options. I'm leaning towards HP Tuners with RTT.

SSpdDmon

iTrader: (10)

That's a decent package. But, I'd highly recommend the EFI Live solution. Having seen both in action, EFI Live has a more user-friendly design, tons of descriptions for the tables, and has a more promising real-time platform when combined with the RR PCM (IMO).

MeentSS02

iTrader: (11)

If it was me, I'd run the least amount of pressure that still allowed me to stay under 80% maximum duty cycle for the injectors chosen.

GIGAPUNK

iTrader: (2)

What's your reasoning?
Lower Amperage draw? Longer Pump life? Higher low-rpm resolution?

How big of an injector do you have to have b4 you need to start worrying about low-rpm resolution?

MeentSS02

iTrader: (11)

The higher low-rpm resolution is definitely a plus, although people don't seem to have much of a problem getting 48-lb/hr injectors to idle, and I'm not sure what the limit is on that one as far as size goes.

Also, a lot of my reasoning comes from what Racetronix posts for their Walbro pump flow rates vs. pressure:

270 L/hr @ 43.5 psi
235 L/hr @ 58 psi

According to those numbers, you trade volume for pressure, which makes sense to me. If you have big enough injectors to be able to lower the pressure, you really shouldn't have to worry about the flow rate being too low as opposed to cranking up the pressure to compensate for a smaller injector. The engine is gonna need a certain volume of fuel to run correctly...with my stock factory pump, I drop a lot of pressure going WOT (drops to 50-52 psi from 58 at idle) just to maintain the volume it needs, artificially driving my injector duty cycle up. Gets pretty annoying, but at least it is repeatable.

Really that's all I'm basing on...I could be way out in left field on this one.