What Size Injectors for Boost Reference Fuel System

pokeyl

Would you run stock injectors as fuel would increase as boost pressure builds. If so factory tune would be close for fuel, you would only need to change timing? MAF should take care of itself up to the point you max out the sensors.

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phunk

No, No, and No.

Rail Pressure 52psi & Intake manifold pressure 0psi = effective fuel pressure 52psi.

Rail Pressure 52psi & Intake manifold pressure 10psi = effective fuel pressure 42psi.

Rail Pressure 62psi & Intake manifold pressure 10psi = effective fuel pressure 52psi.

Referenced regulator is to keep effective fuel pressure the same in boost, rather than it falling off. If you had more boost than rail pressure, you would inject air into the rails rather than fuel into the manifold. If you have 30psi of boost and 52psi in your rails, your effective pressure would be so low (22psi) that you couldnt get injectors large enough and your fuel atomization would suck.

Referencing the regulator in a 370z isnt usually needed until 10psi of boost or more. Unless your injectors are too small, then you might do it sooner.

Referencing a regulator in a 370z should be done to a boost only source (charge pipe), and not a boost/vacuum source like other cars. This is due to inconsistent manifold vacuum from the VVEL system.

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pokeyl

At 10 psi the fuel would go up by 10 psi to 62?

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phunk

a referenced regulator will alter fuel pressure with a 1:1 ratio. 10psi:10psi. That is, if the reference hose is hooked up to it. Otherwise it will just run at a static pressure.

As mentioned, the purpose of the referenced regulator is to keep effective fuel pressure the same. So 10psi:10psi, 40psi:40psi, etc.

So your answer is yes:

Rail Pressure 62psi & Intake manifold pressure 10psi = effective fuel pressure 52psi.

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pokeyl

Got it at 15 psi of boost would need over 100 psi of fuel pressure

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bullitt5897

In a 1 to 1 fuel system yes. I have a 1 to 1 ratio system in my car.

What we found out was that my 1150cc injectors were too small and even with the A1000 on 12V I was not able to stretch the injectors.

We started running a Base Pressure of 40PSI and since we were running 25psi of boost our total fuel pressure was 65psi. At this total pressure my fuel pump was only able to flow ~690lbs/hr which is less than a twin pump design.... at this point we knew the injectors were out of juice. so in order to stretch them we bumped up our base pressure only to get a less than stable top end with the injectors going static and the fuel pump flowing even less.

Fuel pumps flow better at lower pressures the ideal pressure for my fuel pump is 30psi. when we add boost its not enough... so we will be upgrading the fuel pump and injectors.

Fueling for any engine is a balance between injector size and fuel pump pressure.

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phunk

No, you do not need over 100psi of fuel pressure for 15psi of boost.

I think that you are not understanding that your effective fuel pressure is the difference between your rail pressure and manifold pressure.

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phunk

LOL way too much information at this point.

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pokeyl

You would for stock injectors?

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phunk

Ya you would need a ton of fuel pressure to get stock injectors to take you into high horsepower. But they probably wont function correctly at those pressures, and your fuel pump will have terribly low output at that pressure.

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bullitt5897

I know lol... Basically I was trying to portray that in order to stretch an injector you will need a supporting pump, lines, regulator and voltage.

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Shop Cars: 2013 318whp Nismo VspecII 370z *SOLD*, 2009 1000hp+ 93oct 4.0L TT 370z Fast Intentions STAGE 4 #054

bullitt5897

Fuel injectors have an optimal duty cycle. Once you past the maximum duty cycle it is very likely they go static causing instability and lean conditions in your motor. There are some good videos on youtube showing what happens when you go too high in pressure and the Injectors pretty much shut down. 100 psi is insane on stock injectors!

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Shop Cars: 2013 318whp Nismo VspecII 370z *SOLD*, 2009 1000hp+ 93oct 4.0L TT 370z Fast Intentions STAGE 4 #054

roplusbee

What size injectors are you planning to run at this point?

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pokeyl

I have 750cc right now 93 pump fuel

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KratikosG37

Using 750cc because of your NX system?

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