injectors maxing out

[Rev]

Base fuel pressure for the starlet is 2.3/2.4 bar.

Thanks Adam I have seen 2 pressures posted I was considering the worst case but I think it doesnt apply as you say.
I have also seen the 1996 Terecel manual lists 226 - 265kPa fpr pressure ( hose connected) [ Base pressure therefore 2.26bar ]. From what you are saying that will be the base pressure at idle for Starlet.

Wondering do you know for calculating injector size do you use the top or bottom of the fpr range ie 2.26 bar or 2.65 bar for full boost fuel ?
May be wrong but from what I have read the higher fpr pressure is used for cold start , a/c ,colder temp running and idle and is not for raising pressure differential at the injectors above the 2.26bar base pressure?

 

[AdamB]

Thanks Adam I have seen 2 pressures posted I was considering the worst case but I think it doesnt apply as you say.
I have also seen the 1996 Terecel manual lists 226 - 265kPa fpr pressure ( hose connected) [ Base pressure therefore 2.26bar ]. From what you are saying that will be the base pressure at idle for Starlet.

Wondering do you know for calculating injector size do you use the top or bottom of the fpr range ie 2.26 bar or 2.65 bar for full boost fuel ?
May be wrong but from what I have read the higher fpr pressure is used for cold start , a/c ,colder temp running and idle and is not for raising pressure differential at the injectors above the 2.26bar base pressure?

This is one thing where it can get confusing as to whether to use a rising rate type or a fixed type. Either way the fuel pressure should be set with the vac hose disconnected. I've only ever calculated aftermarket injector sizes at specific fuel pressures, so if looking to to find out injector sizes depending on boost applciation (I normally work out based on required fuel flow for the engine), I would work it out using maximum boost pressure.

Here's something I did a little while ago to work out what fuel pump I will need and what size injectors I will need based upon required fuel flow for x amount of HP.

The downside to this method is that fact its based on maximum HP rather than mass air flow. As we know you can run a large GT35 turbo that will move more air at a lower boost pressure than say a td04 at maximum boost pressure. I always add a safety factor by adding on like 5-10% of the maximum HP because this will also counter act any change in air temp, air density, fuel temp etc to ensure that there is enough fuel flow at all times.

 

[Rev]

I am trying to understand the stock ecu better and which fuel pressure to use for the max boost injector size.

Seems ok to calculate on HP as you can push the fuel ratio beyond the air flow and get more power as long as you keep the air flow in mind and dont go too far from max torque afr.

 

[AdamB]

I don't think the fuel pressure would have any relation to the air temp since its a mechanical device, it would simply calculate from using ther IAT sensor, then adjust the injector opening period to suit. Any temperature compensation would be done through the IAT sensor, along with others, and not by increasing the base fuel pressure. I don't believe in tuning through the FPR is the safest and most reliable method, but it does have some use to the system. I think you would need fuel pressure closer to 3 bar at full boost (0.65 bar) to be on the correct side of caution.

 

[Rev]

Ok thanks thats makes sense better control hence why piggybacks increase DC .

In regards to boost Adam your approach seems spot on, with larger injectors and stock pressure using my dyno figures and reverse calculating the injector size, this matches the lower figure in the range of stock fuel pressure 2.26 bar ( vaccum hose on ) at 80DC very closely.


For thiose setting up fprs for more fuel pressure as Adam suggests. Maybe be interested to know the base figures in the Tercel Manual with vaccum hose off are 281-287 Kpa or 2.81bar - 2.87bar .