Let's say I get a fuel pump that flows twice as much as the stock one, with no changes to the engine.

Will the pump be straight up flowing twice as much fuel, or is there something that controls it so it only flows what it needs to?

I've been wondering about this for a while, and would like to understand how it all works before upgrading a fuel pump.

 

The pressure in the rail is the same whether the pump can push twice as much volume or not. The only time you run into problems with this is if the fuel pressure regulator can't flow enough back to the tank. This will cause a pressure to rise in the rail making your car run rich. I think some of the newer vehicles (Ford Focus) they have a fuel pump that is controled by the ECU and it regulates how much pressure the rail sees with out a fpr and return line.

 

So you're saying that the pump will in fact flow twice as much fuel (but the pressure will be unchanged)?

 

Yes, but the pressure will rise if the regulator is not big enough.

 

It will also rise out of control if the return line is overwhelmed by flow, but this is pretty extreme and unlikely using any type of in-tank pump.

Newer cars are quickly going to returnless fuel systems that vary pressure in the tank, so conventional methods of increasing fuel pressure no longer work.

 

Exactly

 

So if i were to switch to a pump from a DOHC b-series, and put it in my car with a SOHC VTEC, it shouldn't affect anything and cause it to run to richly?

 

you are increasing from a 79 lph pump to a 135 lph pump...you will not have any overfueling problems, just more fueling potential.

 

Great! Thank you

 

But still it's kind of useless to get too big a pump, as the thing will pump more fuel for no reason. It's wasteful....anyone agree?

 

the keyword here is "potential"...
..and thanks to everyone else..now i know what that second line is for...


[Modified by 10K2HVN, 12:57 PM 1/16/2003]