Increased fuel pressure: any benefit on port injected engine 2

[inline6]

is there any real tangible benefit from increasing fuel rail pressure from say 3b to 4b in a naturally aspirated engine with injector close to head spraying on the back of the valve?

People say there is better atomisation but has anyone seen real gains in fuel economy, better BSFC, more power/torque or anything from a relatively small change?

i have seen some manufacturers use 5b but could this might be more for emissions? im not really interested in the emission side of things

note i am not talking about increasing pressure to get more flow

thoughts?

thanks

 

[BrianPetersen]

If you go outside the design pressure range that the injectors are designed to operate within, you may encounter difficulty or inconsistency with their opening and closing.

With the injector spraying at the back of the intake valve (conventional), most of the vaporization is going to be governed by heat transfer between the valve and the fuel being sprayed at it. With the injection non-synchronized with the intake stroke, the charge drawn into the cylinder is going to be non-homogeneous anyhow, until turbulence in the cylinder mixes it all up. With fuel bouncing off the walls of the intake port, it's going to do that no matter the pressure.

I don't think you are going to find anything of value by changing the fuel pressure in a port-injected engine; probably more to lose than to gain by doing so.

Spray-guided direct-injection is a whole different ball game.

 

[inline6]

realistically would 3.8b (direct replacement FPR is available) be an issue on a modern multi hole injector? currently running batch fire but have capability to do sequential but just wondering if its worth jumping the pressure at the same time

 

[WGJ]

You would be attending to the fuel maps in the ECU too, I assume, if you increase the fuel pressure?

Bill

 

[Lou Scannon]

PFI rail pressure is a bit of a trade-off, like everything else. What you gain in atomization and penetration with higher pressure, you tend to lose in accuracy and repeatability, down at idle and coasting conditions. It can be assumed that the OEM made their best effort to optimize this trade-off.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[inline6]

Thanks for the replies, yes it would be retuned to suit as i have a standalone ECU with quite good control over most aspects of fuel delivery.

The engine specs bear little resemblance to the OEM setup and more modern engines have used 5b with a similar injection and intake manifold strategy. However i will not be using anything that high as i would probably need to upgrade other things like the pump etc to makes sure the system is reliable in operating at those pressures.

i am using modern injectors (multi hole) and the idle PW is about 1.9-2.0ms and dead time is 0.4ms at 12V so i think there is room to increase pressure somewhat without unpredictable behavior at idle.

i have run about 3.5b previously but this was with the standard computer when i used an adjustable FPR as a means to increase fuel but now the situation is different as I control fueling through the fuel map so a pressure increase would only be worthwhile if there was an improvement in BSFC or similar.

Obviously I can test and find out but I’m not sure that testing methods available to me would be adequate enough to be conclusive.

I have not seen any data through online search comparing economy or output with varied fuel pressure except for direct injection.

 

[dgallup]

There is nothing to be gained if you don't need increased flow due to engine mods. You will end up idling at less repeatable, less linear pulse widths. The injectors were calibrated at the factory pressure, increasing the pressure will cause them to have greater injector to injector flow difference. Sure you can do it but you will gain nothing.

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