I'm wondering what's the lowest fuel pressure you can 'sensibly' use at tickover...
For example - a 3bar fuel rail, with the vacuum pull connected drops to (for arguments sake) 2.5 bar at tickover. Clearly, OEM's know this is suitably low to get a reasonable spray and control out of the injector.
In my case however, I'd like to drop to as low a pressure as possible (there are reasons - which i'll explain later, bear with me for now)!
Clearly, going too far (say 5psi @ rail) will probably make the injector spit random, un-precise globs of fuel out; infact - will the injector even work at this low pressure? maybe not!
So - anyone got any educated guesses / real data? I'm thinking i really shouldn't drop less than 2 bar myself - but dropping to even 1.5bar would be preferable - but obviously, i don't want to lose any response or resolution of the injector - there must be a 'break even' point somewhere though!
D
Minimum fuel rail pressure @ idling vs injector resolution
Moderators: jsmcortina, muythaibxr
I'd say it probably depends on your injectors.
The old D-Jet injection system used a system pressure of only 2.0 bar, and when you hooked up a gauge to the system, it was common to see pressures as low as 1.8 bar with the car still running fine (though obviously somewhat lean). D-Jet also did NOT run a manifold referenced pressure regulator, so pressure across the injector was often 2.5 to 2.7 bar at idle, but dropped to 2.0 bar or less at WOT. D-Jet injectors tend to be really big for their applications, when rated at the usual 3.0 bar pressure. A 60hp VW 1.6, for example, used 275cc/min injectors quite capable of handling 185hp or so. The injectors were run right on the practical limits at idle.
The old D-Jet injection system used a system pressure of only 2.0 bar, and when you hooked up a gauge to the system, it was common to see pressures as low as 1.8 bar with the car still running fine (though obviously somewhat lean). D-Jet also did NOT run a manifold referenced pressure regulator, so pressure across the injector was often 2.5 to 2.7 bar at idle, but dropped to 2.0 bar or less at WOT. D-Jet injectors tend to be really big for their applications, when rated at the usual 3.0 bar pressure. A 60hp VW 1.6, for example, used 275cc/min injectors quite capable of handling 185hp or so. The injectors were run right on the practical limits at idle.
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Re: Minimum fuel rail pressure @ idling vs injector resoluti
We recently installed some Ford 32 pound/hour (337cc/min) injectors in a Honda 1.6L and lowered the rail pressure to 18 pounds (1.2 BAR) at idle. The result is that all operation is identical to the factory injectors that ran at higher pressure - except that the engine has a slight stumble or light miss on very cold startup. The average person would never know we changed the injectors. This light stumble can be eliminated with additional tuning.
The typical injector functions at zero PSI. The measured flow at even 5psi is accurate but may be a drip or dribble. For some engines this is no problem as the airflow at the injector or point the fuel droplets splatter is sufficient to still atomize when carried past the valve and into the chamber. Consider that carburetors used accelerator pump squirters that shot huge squirtgun streams of fuel into the tops of manifolds - nowhere near the valves. They did and still do work quite effectively.
As another example we installed 90 lb/hr TBI injectors on a GM 350 twin turbo project and had to lower the idle pressure to only 4.5 pounds. The effect was similar, and with greater prime pulses and additional accel enrichment, was a good running setup. I think you'd be surprised what may actually work - depending on a variety of factors. Although your idle emissions may be shaggy, good tuning should solve most issues you might find.
What is your application?
David
The typical injector functions at zero PSI. The measured flow at even 5psi is accurate but may be a drip or dribble. For some engines this is no problem as the airflow at the injector or point the fuel droplets splatter is sufficient to still atomize when carried past the valve and into the chamber. Consider that carburetors used accelerator pump squirters that shot huge squirtgun streams of fuel into the tops of manifolds - nowhere near the valves. They did and still do work quite effectively.
As another example we installed 90 lb/hr TBI injectors on a GM 350 twin turbo project and had to lower the idle pressure to only 4.5 pounds. The effect was similar, and with greater prime pulses and additional accel enrichment, was a good running setup. I think you'd be surprised what may actually work - depending on a variety of factors. Although your idle emissions may be shaggy, good tuning should solve most issues you might find.
What is your application?
David
My application is an A-series turbo engine. There is a whole ream of info about this motor, but i'll summarise:
4 cyl, two inlet ports.
Port A feeds cyl 1&2, port B feeds cyl 3&4. Firing order 1342. Hence (port operation) is AABBAABBAABB...
Because of this - we only have a 'theoretical' 180 degrees to get all the fuel into the 'second' firing of each port. Actually - it's less as the first valve isn't closed till 30+ degrees ATDC and port velocity (fuel carrying capacity) drops off quickly as the valve approaches closing.
Basically - it's something like a 60% duty cycle as an absolute max - erring on the side of caution, it's probably more like 50%, maybe even less.
As it's a turbo, with a 7K rpm rev potential - i need a lot of fuel in there - in a short space of time. I'll be upping the fuel pressure 2x boost, and pulling as much of it away at idle - to get the appropriate resolution from the large injector(s)
Thanks for your info - 'tis all good news!
4 cyl, two inlet ports.
Port A feeds cyl 1&2, port B feeds cyl 3&4. Firing order 1342. Hence (port operation) is AABBAABBAABB...
Because of this - we only have a 'theoretical' 180 degrees to get all the fuel into the 'second' firing of each port. Actually - it's less as the first valve isn't closed till 30+ degrees ATDC and port velocity (fuel carrying capacity) drops off quickly as the valve approaches closing.
Basically - it's something like a 60% duty cycle as an absolute max - erring on the side of caution, it's probably more like 50%, maybe even less.
As it's a turbo, with a 7K rpm rev potential - i need a lot of fuel in there - in a short space of time. I'll be upping the fuel pressure 2x boost, and pulling as much of it away at idle - to get the appropriate resolution from the large injector(s)
Thanks for your info - 'tis all good news!
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This is an interesting engine with some interesting possibilities.
My advice is this: Run your 4 giant injectors per port or whatever you're doing there, and add a 5th TBI injector for idle.
Set up dual-table to reflect this setup and then you've got an extra injector if you ever run out of injector on the top end. (Not likely in this setup...)
OR
With two banks of injectors (you're using four, I guess) you could do dual table and use a single bank for idle. (this assumes a common plenum, of course)
The reason I make these suggestions; how are you planning on controling fuel pressure?
-Brian
My advice is this: Run your 4 giant injectors per port or whatever you're doing there, and add a 5th TBI injector for idle.
Set up dual-table to reflect this setup and then you've got an extra injector if you ever run out of injector on the top end. (Not likely in this setup...)
OR
With two banks of injectors (you're using four, I guess) you could do dual table and use a single bank for idle. (this assumes a common plenum, of course)
The reason I make these suggestions; how are you planning on controling fuel pressure?
-Brian
I'm going to be using a Vortech fuel regulator. I can pull the pressure off at idle to whatever i want, and rise it on any ratio proportional to boost (2:1 should be more than enough)...
Ok - confession time; i'm not actually using Megasuirt - but a UK -sourced aftermarket ECU that i already have - but I can't ignore the wealth of knowledge here!
I was planning on using just two injectors - one per inlet tract, but this still might not work.
I can use dual injectors, switching to both and halving the fuel-count at a suitable rev point though - it's more work (not a lot of manifold space to play with), but might be do-able...
If I did this route, I reckon I won't need to drop the fuel pressure mind, as i'll only be running one set of 400cc injectors at idle, which with 2dp in my ECU injection timings, should be controllable...
Ok - confession time; i'm not actually using Megasuirt - but a UK -sourced aftermarket ECU that i already have - but I can't ignore the wealth of knowledge here!
I was planning on using just two injectors - one per inlet tract, but this still might not work.
I can use dual injectors, switching to both and halving the fuel-count at a suitable rev point though - it's more work (not a lot of manifold space to play with), but might be do-able...
If I did this route, I reckon I won't need to drop the fuel pressure mind, as i'll only be running one set of 400cc injectors at idle, which with 2dp in my ECU injection timings, should be controllable...
Last edited by TurboDave on Fri Nov 04, 2005 6:06 pm, edited 1 time in total.
Just wondering:
Is the MS coding 'open' to anyone to have a tinker with, and try to add more code?
Also - What language is it written in?
If I looked into adding some code, who are the bods who can give me a quick overview of the coding (to save me spending hours trying to figure out what the current code lines / applications are)?
Is the MS coding 'open' to anyone to have a tinker with, and try to add more code?
Also - What language is it written in?
If I looked into adding some code, who are the bods who can give me a quick overview of the coding (to save me spending hours trying to figure out what the current code lines / applications are)?