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Old 05-27-2016, 08:05 PM   #1
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Default What fuel pressure, OEM NB returnless

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
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Old 05-27-2016, 08:10 PM   #2
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Nominally 60 PSIG, at the tank.
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Old 05-27-2016, 08:44 PM   #3
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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
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Old 05-27-2016, 08:46 PM   #4
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its not 60psi under boost. its 60psi fixed. it goes down with boost and up top as you near the limits of the pump
basically its only 60psi under perfect conditions (like just idling or normal driving) and just goes down from that
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Old 05-27-2016, 08:53 PM   #5
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Its still 60 psi under boost, its just that the boost pressure opposes it, its actual pressure should still be 60, but its relative pressure should be lower.

Or am I retarded?

Dann
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Old 05-27-2016, 08:59 PM   #6
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different way of looking at it but yeah same conclusion

*edit: although I think someone tested this and the pressure was still diving up top even on an n/a car

its easy to check though, just put a pressure gauge/sensor at the fuel rail
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Old 05-27-2016, 09:11 PM   #7
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Quote:
Originally Posted by 18psi View Post

*edit: although I think someone tested this and the pressure was still diving up top even on an n/a car

its easy to check though, just put a pressure gauge/sensor at the fuel rail
This is the OP question, what happens to it in the real world?
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Old 05-27-2016, 09:25 PM   #8
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Quote:
Originally Posted by nitrodann View Post
Its still 60 psi under boost, its just that the boost pressure opposes it, its actual pressure should still be 60, but its relative pressure should be lower.

Or am I retarded?

Dann
(edit -- I did my math wrong, look down at post 17)
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 02:19 PM.
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Old 05-27-2016, 09:38 PM   #9
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Great answer. Sounds like 300whp on ID725s is about it.

Thankyou for the data.

Dann
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Old 05-28-2016, 12:04 AM   #10
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I have a in car electric fuel pressure gauge with the sender on the FM dbl inlet fuel rail on my 99 and read 60 to 62 psi pretty much consistently no matter if in boost or not with a 255hp walbro.
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Old 05-28-2016, 12:13 AM   #11
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Quote:
Originally Posted by 18psi View Post
different way of looking at it but yeah same conclusion

*edit: although I think someone tested this and the pressure was still diving up top even on an n/a car

its easy to check though, just put a pressure gauge/sensor at the fuel rail
What is the easiest way to do this on the stock rail? Was there a fitting where a sensor could be screwed in?
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Old 05-28-2016, 01:18 AM   #12
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You can probably fit one in place of one of the fuel dampers
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Old 05-28-2016, 01:21 AM   #13
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Quote:
Originally Posted by nitrodann View Post
Great answer. Sounds like 300whp on ID725s is about it.

Thankyou for the data.

Dann
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
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Old 05-28-2016, 01:24 AM   #14
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Quote:
Originally Posted by 18psi View Post
You can probably fit one in place of one of the fuel dampers
You can, but I don't recommend it. The dampers are there for a reason, and losing one makes for significant pressure waves in the rail.

--Ian
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Old 05-28-2016, 01:27 AM   #15
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correct. this would be for testing purposes, not long term
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Old 05-28-2016, 04:57 AM   #16
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Quote:
Originally Posted by codrus View Post
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
Its making 300 on pump, but I would like to know what it can make on E85, I should just check the DC I think.

Thanks for everyones replies.

Dann
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Old 05-28-2016, 12:04 PM   #17
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Quote:
Originally Posted by codrus View Post
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
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.
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Old 05-28-2016, 02:18 PM   #18
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Quote:
Originally Posted by DNMakinson View Post
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.
Duh, you're right, sorry.

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
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Old 05-28-2016, 02:23 PM   #19
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My ~630cc FlowForce EV14s at 9-10psi (~205whp gas) on an NB2 fuel system with a DW200 need about 55%DC on gasoline and 80%DC on E85.
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Old 06-26-2016, 08:41 PM   #20
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Quote:
Originally Posted by Savington View Post
My ~630cc FlowForce EV14s at 9-10psi (~205whp gas) on an NB2 fuel system with a DW200 need about 55%DC on gasoline and 80%DC on E85.
I have the 610cc flowforce ev14s from Trackspeed. Car (1999) has stock fuel system. Hydra ecu. Gt2560r w/ 3 inch straight thru exhaust. 10psi.

Is 610cc big enough to use e85 with an aftermarket fuel pump (dw300 maybe) and an otherwise stock '99 fuel system?
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