Need a logical reason behind a bigger fuel pump...

[Atari007]

I just dont understand the concept of upgrading your fuel pump... I mean... the amount of fuel that you get into the cylinder is not going to be determined by how much fuel your pump flows, but by the fuel pressure regulator... it is still going to determine how much fuel... you know what i mean? I would just like a little clarity on this... i have looked and looked and can not really find a real 'answer'.... can you guys help me out here? I really never even thought about it untill my mechanic sayed that i was a retard for spending money on my walbro 255... we havent installed it yet because now im having second thought about why i really need it..... what do you guys think?? Thanx--

 

[L2RTSiAWD]

Just like a bigger turbo flows more air 15psi than small one.

A bigger pump will flow more fuel at 43psi of fuel pressure than the factory one. Figure in a bigger injector will draw more fuel than the stock pump can put out.

 

[90GSX]

Do not take your car back to that mechanic.

The FPR simply increases the pressure in the fuel rail based on a 1:1 ratio, (+1psi boost = +1psi fuel pressure + base fuel pressure). This does affect the amount of fuel that will enter the cylinders, but only because the added pressure will force more fuel through the injectors when they're opened.

However, the FPR cannot adequately raise pressure if the fuel pump cannot flow enough volume AND pressure to match the requirements. This becomes an issue when modifications to the vehicle begin to increase the volume and pressure of air consumed by the engine. Since the key to any engine, modified or stock is maintaning an ideal air/fuel ratio, it makes sense that if one modifes the vehicle to consume more air, additional fuel will be necessary. If this additional fuel is not supplied (by the pump, not the FPR) the engine will quickly become suicidal.

 

[marshall]

go to a different 'mechanic'...or better yet...do the work yourself!

...marshall

 

[Atari007]

Thanx for the help guys, i was only thinking in terms of pressure, not volume. I understand how the a/f mix works, I just didnt see how the pump would make a differance... and Marshall... not to be an a$$, but I do all my work myself... I just go to my mechanic for guidence sometimes. Thanx--

 

[BatmanGSX]

Originally posted by 90GSX
The FPR simply increases the pressure in the fuel rail based on a 1:1 ratio, (+1psi boost = +1psi fuel pressure + base fuel pressure). This does affect the amount of fuel that will enter the cylinders, but only because the added pressure will force more fuel through the injectors when they're opened.

Wrongo bongo.

The FPR raises pressure to keep the ratio across the injector the same. If the injector flows a certain amount of fuel at a given IPW, with a 43:0 ratio across the injector, it will flow the same with a 63:20 (20psi of boost) ratio at that given IPW.

Simply put, the stock pump cannot support the volume, at higher boost levels and IPWs, especially with bigger injectors. If you are running 20psi of boost on a 20G with 550s, the pump simply will not supply the volume. The pressure will drop off and you will lean out. I estimate the stock pump is good for maybe 105-108mph in the 1/4th. Even that is pushing it. There is no reason not to put a big pump in, it will work now and later.

 

[90GSX]

Originally posted by BatmanGSX
The FPR raises pressure to keep the ratio across the injector the same. If the injector flows a certain amount of fuel at a given IPW, with a 43:0 ratio across the injector, it will flow the same with a 63:20 (20psi of boost) ratio at that given IPW.

Ignoring IPW, assuming the injector is in the open position, would higher pressure in the rail not speed the rate of fuel flow through the injector, thus increasing the volume of fuel output until the injector had reached it's maximimum, say 550cc/min @ (P)psi.?

Simply put, the stock pump cannot support the volume, at higher boost levels and IPWs, especially with bigger injectors. If you are running 20psi of boost on a 20G with 550s, the pump simply will not supply the volume. The pressure will drop off and you will lean out. I estimate the stock pump is good for maybe 105-108mph in the 1/4th. Even that is pushing it. There is no reason not to put a big pump in, it will work now and later.

Read my second paragraph, that's what I said. You need adequate pressure and volume to keep up with modifications because the FPR is not capable of increasing fuel supply, all it does is regulate the pressure in the rail.

 

[mavisky]

the best thing to do is to upgrade the fuel system to larger line so that you can flow more fuel at a lower pressure. less strain on everything.

look into the stevetek fuel system.

 

[BatmanGSX]

Originally posted by 90GSX
Ignoring IPW, assuming the injector is in the open position, would higher pressure in the rail not speed the rate of fuel flow through the injector, thus increasing the volume of fuel output until the injector had reached it's maximimum, say 550cc/min @ (P)psi

No, this is because the pressure on the other side of the injector has gone up as well because there is boost. When the injector sprays into a boosted port you have to increase the pressure inside the rail to keep the rate linear.

It's still a constant pressure ratio. 43psi of fuel pressure spraying into 0psi of boost is the same volume as 63psi spraying into 20psi of boost.

 

[90GSX]

Originally posted by BatmanGSX


No, this is because the pressure on the other side of the injector has gone up as well because there is boost. When the injector sprays into a boosted port you have to increase the pressure inside the rail to keep the rate linear.

It's still a constant pressure ratio. 43psi of fuel pressure spraying into 0psi of boost is the same volume as 63psi spraying into 20psi of boost.

Agreed, but if we increase BFP wouldn't the fuel volume increase? (ceteris peribus)

 

[TSi92]

Interesting... low 12's stock injectors stock pump with a AFPR and an inline fuel pump. http://www.boostedperformance.com

 

[BatmanGSX]

Originally posted by 90GSX


Agreed, but if we increase BFP wouldn't the fuel volume increase? (ceteris peribus)

Yes, but that is not what we are talking about. I don't recommend increasing base pressure unless you are trying to max out 450s or 550s, or you have a 2G and can't get any timing out of it.

 

[NDgsx]

Fuel pump flow drops off at higher base pressure. You actually end up running out of fuel quicker.

 

[BatmanGSX]

Yeah, try running 50psi of base pressure and 30psi of boost and 100% duty cycles on 660s. Even a Walboro might drop the ball.