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Discussion Starter #1 (Edited)
- when a fuel pump fails, can backpressure force fuel through the dead pump backwards, or is a dead pump a block to fuel flow in either direction, regardless of whatever pressure differential might exist on either side of it?

- is there a direct relationship between fuel pressure and flow, i.e. high fuel pressure resulting in less flow (liters/hour), and low pressure resulting in higher flow?

- when dual (or multiple pumps) are used in a system, if the overall fuel loop is pressurized at 4 bar, then will each pump only see 2 bars?
 

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- when a fuel pump fails, can backpressure force fuel through the dead pump backwards, or is a dead pump a block to fuel flow in either direction, regardless of whatever pressure differential might exist on either side of it?

- is there a direct relationship between fuel pressure and flow, i.e. high fuel pressure resulting in less flow (liters/hour), and low pressure resulting in higher flow?

- when dual (or multiple pumps) are used in a system, if the overall fuel loop is pressurized at 4 bar, then will each pump only see 2 bars?
- i cant see why it would make a difference if fuel went back to tank if the pump failed. it would be sod all due to small lines with very low amounts of expansion but i think there should be a non return valve at the pump anyway.

- put simply, yes there is a direct relationship between fuel pressure and flow. higher pressure means more flow at a given injector duty and vice versa

-each pump will have to supply at the same pressure, otherwise one pump will not be able to force fuel at 2bar into a line thats operating at 4bar.

if any of thats wrong im sure someone will correct me:chuckle: :chuckle:
 

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PSI

You should note that the relationship between fuel pressure and flow is a square root one i.e. if you double the pressure you only x1.41 the flow.

Fuel Flow Ratio = √ Fuel Pressure Ratio

Increasing the fuel pressure can result in injector lag or even the injector not opening at all depending on the make of injector and it's operating parameters. I have seen documents where tests where carried out on various modern injectors and some will even operate better at higher pressures with better spray patterns etc but some will also kick the bucket with leaking seals or serious lag/sticking on opening. You can get injector maps for some injectors off the manufacturer that will show the various benefits/drawbacks of differing the fuel pressure.

The amount a fuel pump can flow can DROP if the pressure is too high - as with all things there is a sweet spot for each pump. Pumps can also have bypass valves that open if the pressure is too high buggering everything up :( . High psi also can heat the fuel up from the pump leading to more det. As ever the whole thing is a lot more complex than it would first appear.

There is plenty of information on the web about the whole thing without having to resort to books etc - just do a google on "fuel injectors", fuel pumps etc.
 

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Also forgot to say the fuel filter can also be a block if everything is upped.

There is a general article here on choosing a pump for a Mit 3000GT but the principle is the same for Skylines etc Stealth 316 - Fuel Pump Upgrade Guide

Nissan Fuel Pumps
The Nissan Skyline fuel pump has held a legendary position as the ultimate upgrade fuel pump for the VR4, reportedly flowing 310 lph at 43 psi. Unfortunately, there are no hard data to support this. Nevertheless, some of the Skyline fuel pumps (R33 stock, and HKS and A'PEXi aftermarket) would make excellent upgrade choices for the 3000GT VR4 and Stealth TT.

From what I have read at various web sites, the R32 Skyline came with a 190 lph pump, and the R33 Skyline had a 195 lph pump. I am not sure about the current R34 model. In the April 2004 issue of Turbo & High-Tech Performance magazine, a stock R33 Skyline GT-R fuel pump was tested to flow 252 lph at 43.5 psi and 13.5 volts.

Both Mines and HKS sell upgrade pumps for the Skyline models that flow "only" about 270 lph. The HKS fuel pump (part number 1407-RN019) was also tested in the April 2004 issue of Turbo & High-Tech Performance magazine and it flowed 268 lph at 43 psi and 13.5 volts. The HKS 1407-RN019 and the R33 Skyline fuel pumps tested in T&HTP look just like the 300ZX Turbo fuel pump pictured below.

A'PEXi sells an upgrade fuel pump for the BNR32 and BNR33 Nissan Skyline GT-R. Max Cooper, Home Page, published results of flow tests by RC Engineering for the BNR32 upgrade fuel pump (A'PEXi part number 404-A011) at his web site. This pump outflows any other in-tank fuel pump for 3S cars that has been tested (that I am aware of). With a tested flow of about 300 lph (adjusted for the 6.34 density of the test fluid) at 43 psi and 13.5 volts, six injectors up to 720 cc/min can be supported by this pump. In their 2003 online catalog, A'PEXi shows a list price of $499 for this pump and the one for the BNR33 (part number 404-A010). I have seen prices for this pump at internet stores for between $359.20 (Auto Accessories, Performance Parts, Import Parts, Auto Car Parts) and $410.16 (http://www.overboost.com/). The picture below is from Max Cooper's web page devoted to this fuel pump.
 

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Discussion Starter #5
therefore, it seems that if you have two identical pumps going, where one would be sufficient to do the job, then both will see the same line pressure but flow at half the volume it normally would (kept in check by the fuel regulator). If one pump conks out, the other ought to pick up the slack (as the system can be supported by one pump anyways).

I had my pump replaced by an Apexi. I didn't have a choice in the matter, but now I feel better about it :)
 

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A dead pump doesnt nessecarily mean low fuel pressure.... A fcked pump may still hodl 4bar pressure but half the flow due to a missing blade etc.

Likewise a walboro pump may flow the same as a tomei (hypathetically here) at 3bar but at 7 bar the walboro will be flowing much less.

Most fuel pumps have one way valves in.

Rob
 

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Discussion Starter #7
I had my old pump disassembled and tested on the bench - flow was quite drastically reduced. It wasn't my map - fuel system flow reduction = leanout = preignition = piston meltdown.

That being said, I'm going to be VERY meticulous with my map this time around, and will tune on both a dyno as well as road tuning, using FC-datalogit and a permanently installed wideband O2 with the guy who built and mapped the FD RX7 that took the Korean GT overall championship this year. Will also have a water injection system to cool intake charges on boost, say, about 1 bar and above.
 
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