The reasons that I decided to try running higher base fuel pressure were:

1) My FIC1100s are maxed out (500 whp on E85), and I wanted to avoid buying larger injectors. Higher base pressure gives more fuel (provided that the pump can handle the pressure).
2) I figured that running higher base pressure would be an interesting way to test out the limits of the Walbro 416.

I'm currently at 58 psi base pressure which is getting up there. I got the higher injector flow capacity as I had planned, and I'm still checking out how the pump is handling the higher pressure, but the unexpected benefit is much better off-boost power and overall responsiveness. All I can figure is that the high base pressure is causing a significant improvement in the injector spray pattern.

 

Average fuel droplet diameter is an inverse function of the square root of fuel pressure. What is surprising to me is how a relatively small change like that could make such a palpable difference..

 

I prefer 52psi.

 

interesting tidbit about droplet size. without a doubt i feel it - smoother idle, more power for a given level of vacuum. and it was running well before i raised it. a couple of thoughts about possible reasons for the noticeable improvement.

- last time the injectors were off, there was some gunk. could have happened again, and the higher base pressure may be blasting thru it better.
- off boost performance has always declined a bit in winter presumably due to reduced atomization of ethanol in the colder air. with the higher base pressure, off boost performance feels as good or a bit better than how it does in the summer. when the weather warms up, it may be less noticeable or nonexistent.

 

Im not surprised by your findings 1 bit.

As long as the fuel system as a whole can handle it, more the better.

 

When one considers the ability of the fuel system to handle the pressure, he needs to include the injectors in that equation. Every brand of injector has a maximum absolute design pressure (rail pressure), above which its case may rupture. IIRC, that's ~90psi (6 bar) for the FIC Bluemax, and probably in the ballpark for several other brands. The seamless case design of the Bosch EV14 style is good until around 125psi (8.5 bar).

 

If you have the pump capacity then all the more power to you.

Considering 58 psi, the pump would need to maintain ~88 psi (depending on boost) at max flow.

So, unless the 416 is providing you enough overhead to do that, I don't think this would work for many people.

Definitely an interesting idea and I like the results. Unfortunately, the 416 requires a rewire and I am too lazy to make that step.

Wouldn't there be an increased cooling affect from the depressurization and increased vaporization of the gasoline due to the pressure differential?

 

Im glad you touched on the gunking, I was going to ask about that with the higher base pressure and the atomization change (if any) from the higher pressure.

 

Interesting find mrfred

 

I have my 255 running higher base fuel rail pressure, but I never had it on standard fuel pressure so part throttle drivability is unknown.....

 

I have always wanted to run a static fuel pressure at like 80psi just to see how the car would react to it. With your results, I might just give it a try.

So just un hook the vaccum port from the regulator and set it at 80psi, and watch the magic.

 

Not quite that simple. The pump flow rate drops as pressure rises. The flow rate on most in-tank pumps begins to drop rapidly after 90 psi and then falls like a rock after 100 psi. I don't think a Walbro 255 will even flow at 100 psi. A car running 30 psi of boost probably should have a base pressure no higher than 60 psi (90 psi - 30 psi = 60 psi), and realistically, probably should be no more than 55 psi because there is an additional back pressure due to fricitional losses of the fuel moving through the fuel lines. Also, the stock dual voltage setup doesn't work well with really high base pressure. The pump can stall out pretty easily in low voltage mode if the base pressure is too high. I'm definitely pushing the limit by going to 58 psi - the Walbro 416 might be one of the few pumps that can handle that kind of pressure.

So best to turn up base pressure in 5 psi increments while watching AFR. Assuming that the pump can supply the necessary fuel, the injectors scaling will neet to be adjusted for the additional flow.

 

 

Think there are any benefits due to injection angle?

For example, say you have 1000cc injectors at 100% duty cycle with 3bar base pressure. You up the fuel pressure to 5.5bar and pick up about 30% more injector flow. Now you can run about 75% IDC for the same flow rate. You now have 1/2 a crank rotation where the fuel injector isn't spraying fuel. Think it's enough to allow you to start playing with injection angle? Or do you think you would need IDC under 50% or so for injection angle to really matter much?

 

I once read in a book about EFI systems (forgot the title) that it is best to keep peak IDCs below 65-70% at redline, and to tune injection time in such a way that all the fuel injection is done while the intake valves are open. I would imagine this to be even more important with an alcohol-based fuel...