[kismetcapitan]

if the stock fuel pressure is 3 bar and stock injectors are rated for 444cc flow per minute at that pressure, is there a formula by which one can work out what the flow would be at 3.5 bar or 4 bar? I've got a Nismo fuel regulator and when remapping I'd like to know so I can calculate what's actually going on and going through my injectors.

 

[GarethK]

The flow is a square root factor of the pressure (To double flow you have to quadruple the pressure):

((new pressure/old pressure)^0.5) x old flow= new flow

444cc at 3 bar is
480cc at 3.5 bar
513cc at 4 bar.

This can't be 100% accurate as there are opening / closing time issues etc but it's a good starting point.

If you're going to up the pressure make sure you run the car with a fuel pressure gauge to make sure that it can maintain 4 bar differential at full flow.

 

[ISJ]

enlighten me here; if you are running towards the top rate of your injectors you can up the fuel pressure to compensate (to a degree) therefore negating the need to buy whole new larger injectors

 

[GarethK]

To a certain extent yes - though the higher fuel pressure is subject to your pump capacity etc etc. I wouldn't have much problem going from 3 up to 4 bar to get ~510cc but wouldn't go any further than that and would make sure i fitted a fuel pressure gauge to make sure the pressure wasn't dropping at high flows.

 

[kismetcapitan]

right, that's the technical info I needed. I've got the regulator and I'll bump it up to 4 bar, then set my Power FC as if it's looking at 513cc injectors, and see how it goes. Worst comes to worst, I can always reset it back to normal

looking at 555cc injectors at the moment as at .85bar boost I'm getting up to 95% injector duty - not good, especially as I want to raise boost to 1.1bar. But the adjustment is a good idea I think as well, plus a bit of a stopgap.

 

[GarethK]

Make sure you run it for at least a while with a pressure gauge on. If the pump isn't up to the job the pressure will drop at the highest flow rates and you'll go lean which you DON'T want!