155 replies to this topic

[haggi961]

I was told that its 4.5 bar around the 370bhp mark for the vxr injectors.

[chris_uk]

Which would be silly to run at because of the increase in intake temps.. 350/360 max And at that power vxr inj should be fine.

[oakmere]

Remember the VXR injector was specified OEM for a car producing 240bhp. I am sure GM would not be using these for a 300bhp + engine so why try and make them work upping pressure (which puts more demand on the rest of the fuel system) when you can use a larger injector? I can't believe the VXR injector is below 80% duty cycle even at 330bhp.

[chris_uk]

Why would it put strain on the fueling system with a pump that can cope (500ltr a min pump) the only thing needed to be worried about is the inj. I suppose we can see what mike gets after mapping and i can see what i find when i go.

[Exmantaa]

What fuelpump delivers 500ltr a min?

Pump curves;
And according to this graph@ 4,5-5 bar static + 1,5 bar boost => 80-90psi fuelpressure the Walbro 255 is more a 155...

Edited by Exmantaa, 16 April 2013 - 11:00 AM.

[chris_uk]

Sorry i meant litre per hour not min. http://www.glencoelt...fuel-pump-1965/ This is the pump i have in tank now. Voltage DC:- 12 Flow Ltr/Hr (Max):- 516 Flow Ltr/Hr @ 3 Bar (44psi):- 420 Flow Ltr/Hr @ 5 Bar (73psi):- 390 Max Pressure (Bar):- 8.3

Edited by chris_uk, 16 April 2013 - 11:20 AM.

[siztenboots]

500l/min would make for a quick pitstop refuel

[chris_uk]

3.8bar (56.24psi) + 1.5bar (22.2psi) = 5.3bar (78.44psi) 4.5bar (66.60psi) + 1.5bar (22.20psi) = 6.0bar (88.80psi) So as i understand it my new pump is more than capable than supplying the fuel. With the higher fuel pressure under an over estimates 1.5bar boost pressure. On the m62 i think the max boost on the 2.9 pulley was 12psi @ 7000rpm. The harrop with a 2.9 pulley is 19psi.

[slindborg]

lower (eg more normal) fuel pressure = cooler fuel, less energy wasted pumping it and other such niceness.

[siztenboots]

is that fuel pressure relative to inlet manifold pressure , or absolute ?

[chris_uk]

Would it really make that much difference from 3.8 bar to 4.5 bar to the temps of fuel? Is there any tech sheets showing the duty cycles and such of the 2 injectors?

[Exmantaa]

My mate with a Harrop 80mm (3.15") pulley sees 1.45bar @7500rpm, but that's on a ported 2.0 with a still restrictive exhaust. So the whole system needs to be looked at to say something about boost pressure. Consensus is that you simply have to look thoroughly to your whole fuelsystem; from pump till injectors. In our 2,0 (LSJ) Harrop builds the VXR's simply cannot cope with the needed flow at higher rpm's, so therefore we use the Siemens 60's at standard rail pressure.

[Nev]

Remember the VXR injector was specified OEM for a car producing 240bhp. I am sure GM would not be using these for a 300bhp + engine so why try and make them work upping pressure (which puts more demand on the rest of the fuel system) when you can use a larger injector? I can't believe the VXR injector is below 80% duty cycle even at 330bhp.

If it's any help, when I was remapped at Courtenays, I got them to give me the metrics output. I had Astra VXR injectors in the engine at the time and from this calculated my injector duty cycle was exactly 80% at maximum using a 3.3 Bar FPR.

HTH.

[Exmantaa]

Duty cycle depends on injectorflow (pulse width) and rpm's: http://injector-reha...m/shop/idc.html

[siztenboots]

and voltage ?

[oakmere]

Nev Was that stage 4?

[chris_uk]

Remember the VXR injector was specified OEM for a car producing 240bhp. I am sure GM would not be using these for a 300bhp + engine so why try and make them work upping pressure (which puts more demand on the rest of the fuel system) when you can use a larger injector? I can't believe the VXR injector is below 80% duty cycle even at 330bhp.

If it's any help, when I was remapped at Courtenays, I got them to give me the metrics output. I had Astra VXR injectors in the engine at the time and from this calculated my injector duty cycle was exactly 80% at maximum using a 3.3 Bar FPR.

HTH.

This is whats confusing me.. All these random numbers.

So if they were maxed at 3.3bar for you does that mean my injectors are running at above 80% duty because im at 3.8bar?

Im having difficulty putting these seemingly random numbers into any type of meaning.

[slindborg]

and voltage ?

Voltage has the more profound effect on opening/closing speed, so in theory yes it does change the duty but not as much as is hinders opening for timing purposes.

[chris_uk]

Im trying to make sense of this, Duty cycles are dependant on revs thats right isnt it? So every 2 crank revolutions you get 1 spray of fuel. So for simplicity lets say that you max your rpm at 1000rpm, so that injectors have to squirt 500 times in 1 minute to keep up with the rpm. Lets say that the inj are capable of squirting 1000 squirts per min this means its duty cycle is 50% Is this all 'duty cycle' means? Just the amount of time the inj can spray..?

Edited by chris_uk, 16 April 2013 - 01:08 PM.

[techieboy]

It's how long an injector is open and delivering fuel, so also depends on how much fuel it needs to deliver.