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Fuel Pressure Maxed out

 
Old 05-24-2019, 05:33 PM
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Default Fuel Pressure Maxed out

I am getting tuned on e85 and am running out of fuel. I am up to 95% duty cycle on a walbro 450 and Id1000s. At max boost, 14psi, I hit 76 psi with 60 psi base pressure. I upped the base pressure to 65 psi and still only maxed out at 76 psi.

At first I thought it was because I have the non-high pressure version of the 450 but I am still maxing out at 76 psi after installing the 450 high pressure model. I am running an AEM fpr with the largest orifice. What could be wrong? I am trying to bump my fuel pressure to ~85 psi to lower my duty cycle.
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Old 05-24-2019, 07:24 PM
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Just a guess, but it sounds like the AEM FPR may be at its limits. Have you tried lowering your base pressure to 47 psi to see how it responds?
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Old 05-24-2019, 10:28 PM
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ID1000s 4-450 max on E85... get larger injectors.

And those AEM Rail Fprs aren't the best at all... you'll need -8 feed to a external aeromotive regulator.

Anything over 450, you should be looking at 1650s/1800 injectors, and a real fuel return system.
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Old 05-25-2019, 05:07 AM
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Lower fuel pressure responds better. It actually rises 1:1 with boost. At higher pressures, it starts to top out.

The 450 high pressure is supposed to be able to deliver 112 psi maximum so I don't understand why I'm maxing out at 76 psi. I've got the largest orifice installed on the aem... Maybe it's letting too much flow bypass? A larger return line is gonna provide less restriction and less pressure...
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Old 05-25-2019, 04:27 PM
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You know, high fuel pressure is BAD right? I think alot confuse high fuel pressure equals more fuel, but that's not really the case.

match your goals with your injectors, and the pump deliver the flow for the injectors.

You're just out of fuel, upgrade injectors.
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Old 05-28-2019, 11:30 AM
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Originally Posted by AP1Chief View Post
You know, high fuel pressure is BAD right? I think alot confuse high fuel pressure equals more fuel, but that's not really the case.
Well it sort of does mean more fuel, just not through injector pulse width, but more fuel being injected within the same pulse width. When you close the ability for the return to take the fuel via fpr it only has one way to go which is more fuel and pressure to the rail/injector. Its the primary way a stage one supercharger works with stock injectors and no EMS. My hunch is the orifice on the OP's AEM fpr is too large to get more then 76psi.
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Old 05-28-2019, 11:32 AM
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Originally Posted by jdmz View Post

The 450 high pressure is supposed to be able to deliver 112 psi maximum so I don't understand why I'm maxing out at 76 psi. I've got the largest orifice installed on the aem... Maybe it's letting too much flow bypass? A larger return line is gonna provide less restriction and less pressure...
Yes, closing the return is how you increase pressure to the injector. Your bigger return line im sure is the issue.
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Old 06-03-2019, 10:39 AM
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Like @AP1Chief said, you need larger injectors. 1000cc on E85 will only net you 350 to 400whp on a proper tune. Being at 95% DC should tell you right away youre maxed out. For reference, my 1300cc injectors made 435whp at around 90% INJ DC and 45psi at fpr iirc. If you want more boost, go with 1700 or 2000cc injectors.

And lower your fuel pressure back down to 45-50psi. You're putting a lot of strain on your fuel components running 76psi. The fpr will probably prematurely fail constantly holding that much pressure. You can always mess with parts to make "a little more" power but its not ideal. Try to run all your parts at ideal levels. And if you run out of room, its probably a sign you need to upgrade that component.
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Old 06-04-2019, 01:01 AM
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I just seek clarity: will 1000cc injectors net you more than 400whp on gasoline?
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Old 06-04-2019, 01:28 AM
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The flow is proportional to the square root of the pressure. So yes, increasing the pressure does generate some more flow but not that much, and it adds problems due to the higher pressure.
The best way to add some flow is definetly to change the injectors.
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