jdmrbust

After calculating the flow rate of the stock system with 550cc/min inj in a s4 t2 at the stock fuel system press and then changing that pressure (of th FPR)to 60 psi the injectors now push 730cc/min. Is there any reason against running a new fpr at this rate instead of uprgrading to four 720cc/min inj at the stock fuel pressure?

jgrewe

iTrader: (1)

If you go to high on pressure it will affect the injector closing. Sorry, don't know how high 'to high' is for sure, I don't think 60 will be a problem though.

Crusader_9x

I dont know what pump you plan on using but when going up in pressure the flow is greatly reduced.

pistonsuk

What he said here is true, and is is not a linear relationship (pressure vs. flow). It is unique to every brand/model of pump, the manufacture might be able to give you the "charateristic curve" of the pump.

Also take into account that a boosted car will add 1:1 psi increases to the base pressure under boost. So 60psi base at 15psi boost will be 75psi fuel pressure, which means even more of a reduced flow under the conditions which it needs the most.

Justin

maxcooper

This thread has a few mistakes:

1. 550s at 60psi do not give 730 cc/min of flow. They give SQRT(60/43.5) * 550 = 674 cc/min of flow. The 550 cc/min rating was measured at 43.5 psi.

2. If your pump can't maintain the fuel pressure you ask for, that pump DOES NOT WORK for your setup. You can't tune the car when the pressure drops off, since it will change when you run the fans, wipers, headlights, stereo, etc. And while it is true that pumps flow less at high pressure, you really won't get literally less fuel delivered by upping the pressure (think about what happens when the pump can't flow enough -- the pressure drops!). But again, if your fuel pressure drops off, your pump is not applicable for your car. One option is to turn the fuel pressure down and hold the injectors open longer. Or you might just need a new pump.

Use my web page to figure out your fuel system requirements/capacity:
http://maxcooper.com/rx7/how-to/fuel_system/calcs.html

-Max

bobybeach

spray patern improves slightly but the increase in flow is minimal. i think you just have to bite the bullet and go bigger injectors.