What fuel pressure, OEM NB returnless
#1
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Hi,
Id like to know exactly what fuel pressure returnless NB's have.
I understand that they are pressure referenced, Id like to work out what I can make with maxxed 725's on E85.
I understand that it is 60 psi, can somebosy please confirm? I have an NB8B which is fuel limited at 230whp with RX8 yellows, which seems very low... I should buy a fuel pressure test rig for my dyno.
Thanks,
Dann
Id like to know exactly what fuel pressure returnless NB's have.
I understand that they are pressure referenced, Id like to work out what I can make with maxxed 725's on E85.
I understand that it is 60 psi, can somebosy please confirm? I have an NB8B which is fuel limited at 230whp with RX8 yellows, which seems very low... I should buy a fuel pressure test rig for my dyno.
Thanks,
Dann
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But does anyone have data to show its actually really 60psi under boost in the real world?
Wait, can I do a pull on gasoline, check the duty cycle, add 30% and find my new duty cycle, Im not sure thats accurate enough.
Dann
Wait, can I do a pull on gasoline, check the duty cycle, add 30% and find my new duty cycle, Im not sure thats accurate enough.
Dann
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It is 60-ish psi gauge (I measured mine at 62), and the regulator is relative to the pressure inside the fuel tank, which might or might not be ambient. Since it's pressure relative to the manifold that matters for fuel delivery, this means you have roughly 57-58 psi pushing the fuel out at idle, 47 psi at WOT NA, and 32 psi at 15 pounds of boost.
If you upgrade the pump to a high-flow one, you probably will overwhelm the stock regulator at idle/low load. I measured mine as high as 80 psi with a walbro 255, but the value depends on the system voltage, condition of the pump, and a bunch of other things.
--Ian
Last edited by codrus; 05-28-2016 at 01:19 PM.
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--Ian
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550cc/min injectors did 270 rwhp for mw with high 70s of duty cycle, so 725s should be plenty of injector for that, especially since you can run IDs at higher duty cycles than the older tech RCs I had. OTOH, 300 who is probably more than the stock fuel pump can flow, mine ran out around 250-260, although that depends on what manifold pressure you're running.
--Ian
--Ian
Thanks for everyones replies.
Dann
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It is 60-ish psi gauge (I measured mine at 62), and the regulator is relative to the pressure inside the fuel tank, which might or might not be ambient. Since it's pressure relative to the manifold that matters for fuel delivery, this means you have roughly 57-58 psi pushing the fuel out at idle, 47 psi at WOT NA, and 32 psi at 15 pounds of boost.
If you upgrade the pump to a high-flow one, you probably will overwhelm the stock regulator at idle/low load. I measured mine as high as 80 psi with a walbro 255, but the value depends on the system voltage, condition of the pump, and a bunch of other things.
--Ian
If you upgrade the pump to a high-flow one, you probably will overwhelm the stock regulator at idle/low load. I measured mine as high as 80 psi with a walbro 255, but the value depends on the system voltage, condition of the pump, and a bunch of other things.
--Ian
As stated above, this assumes tank is vented to atmosphere or has no pressure or vacuum.
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I realize that Dann, has his answer, but I question the above information. At idle, Manifold is at -10psig for 30kPa absolute. Therefore, differential across injectors is 70 psi, not 58. Similarly, at MAP=100kPa, differential would be exactly gauge or 60 (less pressure drop due to fuel flow).
As stated above, this assumes tank is vented to atmosphere or has no pressure or vacuum.
As stated above, this assumes tank is vented to atmosphere or has no pressure or vacuum.
I don't know what tank pressure normally is. It hisses when you open it at a gas station, so it's not exactly ambient, but I don't know how big the differential can get before the relief valve(s) open.
--Ian