Discussion and questions related to the course Practical Dyno Tuning
The industry standard base fuel pressure is 43.5 psi and is sufficient even for most V8s engines. If I have a 6 cylinder would it supply ample fuel at 75% of 43.5psi? What is the lowest base fuel if we have plenty of fuel injector assuming lower fuel pressure requires greater injector pulse width?
When would I want to increase base fuel pressure? When IDC % is 80%+ at high VE areas of fuel map?
If I am Wanting to reduce/lower the injector contamination deviation % -Reducing over all fuel pressure I think will have a more accurate fuel delivery. How low can base fuel pressure be and remain consistent fuel delivery?
What is max fuel pressure most Hi-imp injectors are rated/stable?
Thanks for your help.
Need more information.
What injectors do you have, and do you have returnless or return fuel system? Newer generation port fuel systems are designed for returnless fuel and say 5 bar fuel pressure. Older 90s systems run return lines and around 3 bar [43.5psi] and 80s systems are running around 2.5 bar, and of course really old mechanical fuel injection was lower.
As you lower the fuel pressure this will have an affect on the spray pattern and atomisation of the fuel - Usually for the worse. The effect of this is going to depend on the engine, injector location, and about a million other parameters so it's hard to be very specific. I don't think I've ever needed or wanted to drop the base fuel pressure below 3 bar in my career. To give you an example of what's achievable with the current crop of EV14-based injectors, a few years back I was forced to fit a set of 1000 cc injectors to a naturally aspirated Honda B18C due to availability and time constraints . Overkill would be an understatement and I believe we were seeing peak duty cycle in the region of 38-42%. Despite this I could still achieve a perfectly smooth idle at stoich since the injector's minimum fuel delivery was well below what the engine needed at idle. This actually gives some potential advantage though as we then have the opportunity to move the injector timing around under high load/rpm where a traditionally sized injector would be open for most of the engine cycle.
It's not the actual fuel pressure that the injector cares about, but rather the differential pressure (fuel pressure - manifold pressure). The pressure limit however is very dependent on the actual injector design. Some of the newer injectors such as the ID1050X are rated to 145 psi max.