With all the recent threads about fuel pumps, it got me thinking about something...

People say that a 255lph is required for higher dry shots, but that a 190lph is enough for higher wet shots.

Okay, with that in mind, let's say it takes X amount of fuel to keep a 12:1 a/f ratio when you are WOT n/a. And let's say it takes an additional Y amount of fuel to sustain the 12:1 a/f when you are spraying a high nitrous shot, i.e. 125 shot. So, that means you need a total of X+Y amount of of fuel when spraying, correct?

So why is it that it takes a 255lph to sustain a 125 dry shot, but it only takes a 190lph to sustain a 125 wet shot? The only difference I see is that the additional Y amount of fuel is dispersed through the fuel injectors for dry, and the additional Y amount of fuel is injected through the fuel nozzle for wet. Regardless of dry or wet, the fuel pump is still pumping out X+Y amount of fuel, right??

Or am I missing something here?

 

What you are missing is that the extra pressure required for the dry system dramatically reduces the capacity of the pump.

The wet system delivers fuel at 43 psi at WOT for all shots. The dry system requires approx 100 psi for a 125 shot. In the chart below you can see the fuel delivery for both the 190 standard pressure pump and the 255 high pressure pump. You can also compare the others as well. What you see is that the 190 standard pressure pump will deliver much more fuel with a wet system that the 255 high pressure pump will with a dry system.

 

Ahh, thanks Jim. So, by using a water hose as a crude analogy:

190lph @ 43 psi -> wide low powered stream (like what you would use to fill up a bucket)
255lph @ 100 psi -> narrow high powered stream (like a pressure washer)



(Referring to dry kits) In order to supply additional fuel w/o a supplemental fuel nozzle/injector for any application, one would need any one of the following:
1) larger fuel injectors
2) using current fuel injectors, extend the pulse width
3) using current fuel injectors, greater PSI

Seeing that options #1 & #2 require the cost of new injectors and/or ECU programming, I assume that the simplest and cost effective way for dry kits to provide additional fuel is to simply raise fuel pressure via the FPR (option #3)...thus the need for a high pressure fuel pump. Then again, if for some reason, you already have option #1 or #2, a 190lph would suffice.

haha...I think I'm answering my own question here...