How Do 550cc Injectors Make 300rwkw On An Rb25det?

[joeyjoejoejuniorshabadoo]

it seems the op wont be happy until he sees someone say they can't paul...

how many people have proved you can make it?

11ty

/thread

[mattymagoo22]

Hey,

Stock, the Nissan turbo regulator applies a 1:1 change in fuel pressure along with manifold pressure.

Fuel pressure is negated by boost so the net effect is 43psi of fuel pressure regardless of boost/vac.

Some example figures (sorry about underscores):

base___manifold__fuel____net fuel___when

43psi__-7psi_____36psi___43psi_____idle (i.e. manifold vacuum)

43psi___0psi_____43psi___43psi_____no boost, no vac

43psi___20psi____63psi___43psi_____20psi boost

A rising-rate regulator does a different thing - changes fuel pressure by some multiplier other than 1 along with boost; both the rate and the threshold "it starts working at" may be adjustable.

Corky Bell claims to have brought the "original" rising-rate regulator to the market according to Corky's comments on FPR

Some of his regulators are designed to workalongside the existing regulator, some replace it completely.

For example, the rate might be set to 2:1 and the threshold, 0psi of boost. Then we have some example figures:

base___manifold__fuel____net fuel___when

43psi___-7psi____36psi___43psi____ idle (manifold vac, no regulator action)

43psi____0psi____43psi___43psi____no boost, no regulator action

43psi____1psi____45psi___44psi____1psi boost, +2psi fuel pressure, +1psi net extra fuel pressure

43psi____20psi___83psi___63psi____20psi boost, +40psi fuel pressure, +20psi extra fuel pressure

Cheers,

Saliya

Forget about manifold pressure, i'm referring to the actual pressure that you'll see with a gauge inline. Max fuel pressure is approx 40psi or so, the pumps don't pump it any harder than that I thought, maybe I need to read up on rising rate regs, even with the return line clamped you'll see 40 psi max so how can extra pressure be available (someone explain) ??? All that little vacuum line does for a FPR is lift a valve of its seat no extra pressure is pumped into the system its just a sealed diaphragm.

Mate I think you should go have a read on how fuel systems work before you hand out advice. 80% duty cycle is preferred and its well documented why, fuel pressure regs do increase/decrease fuel pressure depending on the vacuum/boost in the manifold.

Yeah because as soon as you hit 81% duty cycle your engine automatically explodes!!!! Do you even know what duty cycle is? You need to put away your fast fours mag and get your hands dirty, my r33 gts-t ran 96% duty cycle for over a year without a problem you going to tell me i'm wrong? And for the record when the FPR has vacuum applied to it the line pressure will be around (from memory) 25-30 psi because the diaphragm lifts the seat and allows fuel back to the tank via a return line so even though the pump is at 40psi the line pressure is much lower than that. Under WOT or boost conditions the FPR is closed bringing line pressure up to 40psi the boost you run on top of that does not change that figure. The boost you run doesn't increase the pressure in the line it just closes it off to lift pressure.

[Adriano]

If you clamp the return line, the fuel pressure will go over 100psi with a good pump(ie not a stuffed one)

[mattymagoo22]

Wow never seen that before, seriously wow.

[JonnoHR31]

Forget about manifold pressure, i'm referring to the actual pressure that you'll see with a gauge inline. Max fuel pressure is approx 40psi or so, the pumps don't pump it any harder than that I thought, maybe I need to read up on rising rate regs, even with the return line clamped you'll see 40 psi max so how can extra pressure be available (someone explain) ??? All that little vacuum line does for a FPR is lift a valve of its seat no extra pressure is pumped into the system its just a sealed diaphragm.

Yeah because as soon as you hit 81% duty cycle your engine automatically explodes!!!! Do you even know what duty cycle is? You need to put away your fast fours mag and get your hands dirty, my r33 gts-t ran 96% duty cycle for over a year without a problem you going to tell me i'm wrong? And for the record when the FPR has vacuum applied to it the line pressure will be around (from memory) 25-30 psi because the diaphragm lifts the seat and allows fuel back to the tank via a return line so even though the pump is at 40psi the line pressure is much lower than that. Under WOT or boost conditions the FPR is closed bringing line pressure up to 40psi the boost you run on top of that does not change that figure. The boost you run doesn't increase the pressure in the line it just closes it off to lift pressure.

wrong, wrong and wrong

as adriano said, clamp the line and fuel pressure will go off the end of a normal gauge with any properly working efi pump. its been said enough times, fuel pressure is referenced to manifold pressure. the reg constantly keeps fuel pressure 43psi above manifold pressure.

if your so certain your reg holds 40psi under boost then try taking the vac line off. if your right it'll be perfectly fine....

Edited February 14, 2010 by JonnoHR31

[saliya]

Forget about manifold pressure, i'm referring to the actual pressure that you'll see with a gauge inline. Max fuel pressure is approx 40psi or so, the pumps don't pump it any harder than that I thought, maybe I need to read up on rising rate regs, even with the return line clamped you'll see 40 psi max so how can extra pressure be available (someone explain) ??? All that little vacuum line does for a FPR is lift a valve of its seat no extra pressure is pumped into the system its just a sealed diaphragm.

Hi,

This _is_ the actual pressure that you'll see with a gauge inline. Those figures for a stock regulator GTR were read straight off the fuel and boost gauges either side of my wheel.

Yeah because as soon as you hit 81% duty cycle your engine automatically explodes!!!! Do you even know what duty cycle is? You need to put away your fast fours mag and get your hands dirty, my r33 gts-t ran 96% duty cycle for over a year without a problem you going to tell me i'm wrong? And for the record when the FPR has vacuum applied to it the line pressure will be around (from memory) 25-30 psi because the diaphragm lifts the seat and allows fuel back to the tank via a return line

I personally don't see a problem with running injectors up to 99.99% provided _all_ mapping points are mapped and the injector manufacturer says it's OK to do so.

However, since it's virtually-impossible to map all load points and correction factors during a tune (e.g. inlet air temp) most people like to leave "some room" for when these things change.

so even though the pump is at 40psi the line pressure is much lower than that. Under WOT or boost conditions the FPR is closed bringing line pressure up to 40psi the boost you run on top of that does not change that figure. The boost you run doesn't increase the pressure in the line it just closes it off to lift pressure.

I get the feeling you don't believe me - put a gauge on your own car, take some measurements, and you'll learn something new. I wouldn't advise popping the vac line off your reg unless you like boost-induced leanouts.

Cheers,

Saliya

[MBS206]

Forget about manifold pressure, i'm referring to the actual pressure that you'll see with a gauge inline. Max fuel pressure is approx 40psi or so, the pumps don't pump it any harder than that I thought, maybe I need to read up on rising rate regs, even with the return line clamped you'll see 40 psi max so how can extra pressure be available (someone explain) ??? All that little vacuum line does for a FPR is lift a valve of its seat no extra pressure is pumped into the system its just a sealed diaphragm.

Yeah because as soon as you hit 81% duty cycle your engine automatically explodes!!!! Do you even know what duty cycle is? You need to put away your fast fours mag and get your hands dirty, my r33 gts-t ran 96% duty cycle for over a year without a problem you going to tell me i'm wrong? And for the record when the FPR has vacuum applied to it the line pressure will be around (from memory) 25-30 psi because the diaphragm lifts the seat and allows fuel back to the tank via a return line so even though the pump is at 40psi the line pressure is much lower than that. Under WOT or boost conditions the FPR is closed bringing line pressure up to 40psi the boost you run on top of that does not change that figure. The boost you run doesn't increase the pressure in the line it just closes it off to lift pressure.

Go do some reading boosted EFI FPR setups...

[Rolls]

I personally don't see a problem with running injectors up to 99.99% provided _all_ mapping points are mapped and the injector manufacturer says it's OK to do so.

However, since it's virtually-impossible to map all load points and correction factors during a tune (e.g. inlet air temp) most people like to leave "some room" for when these things change.

The problem is above around 90-95% the injector will be static and completely open anyway. Sure it'll be getting a 0.9 pulse to the injector, but the injector is mechanical and physically can't open and close in the time of the off pulse so anything around 90-95% technically is maxing it out. Depending on the injector you might get some more flow at 100% but it wont be a linear increase, it will drop drop off severely around 90%.

Here is an image to demonstrate what you are likely to see.

So as most people have said, you should always aim for not much more than 80% duty cycle.

Edited February 14, 2010 by Rolls

[Harey]

Go do some reading boosted EFI FPR setups...

Oh SNAP!

[mattymagoo22]

wrong, wrong and wrong

as adriano said, clamp the line and fuel pressure will go off the end of a normal gauge with any properly working efi pump. its been said enough times, fuel pressure is referenced to manifold pressure. the reg constantly keeps fuel pressure 43psi above manifold pressure.

if your so certain your reg holds 40psi under boost then try taking the vac line off. if your right it'll be perfectly fine....

I get what you're saying in reference to constant 43psi in relation to manifold, just never seen any factory efi pump get that high( i've looked at quite a few). Obviously i'm wrong, guess you learn something new every day.

Cheers.

P.S for the record I did mention that I might need to be some research in an earlier post, just thought I know how it worked, i didn't, now i do. I'm always open to new info even if I am a stubborn so and so.

[saliya]

The problem is above around 90-95% the injector will be static and completely open anyway. Sure it'll be getting a 0.9 pulse to the injector, but the injector is mechanical and physically can't open and close in the time of the off pulse so anything around 90-95% technically is maxing it out. Depending on the injector you might get some more flow at 100% but it wont be a linear increase, it will drop drop off severely around 90%.

Hey,

Cheers for the data, but if you're mapped for the load/RPM and you have the right AFRs, it doesn't _really_ matter whether the injector is open for 100%, 90%, or 20% - it's still correctly-mapped.

I would assume that if this is a common property to all injectors, the ECU's corrections for "slightly-off-map" points would account for it where extrapolation is required.

As an aside: that graph looks like simple PWM input vs flow output (the ECU's correction for lag time may not be included).

So I still think the idea of "allowing 20%" is antiquated Maybe someone that does this for a living could step in and provide some real-world data?

I know only what I've seen on my own car(s).

Cheers,

Saliya

[Harey]

Hey,

Cheers for the data, but if you're mapped for the load/RPM and you have the right AFRs, it doesn't _really_ matter whether the injector is open for 100%, 90%, or 20% - it's still correctly-mapped.

I would assume that if this is a common property to all injectors, the ECU's corrections for "slightly-off-map" points would account for it where extrapolation is required.

As an aside: that graph looks like simple PWM input vs flow output (the ECU's correction for lag time may not be included).

So I still think the idea of "allowing 20%" is antiquated Maybe someone that does this for a living could step in and provide some real-world data?

I know only what I've seen on my own car(s).

Cheers,

Saliya

The 80% is not a hard and fast rule. Its just a guide when you are sizing injectors. That way it gives you a bit of room if you underestimate your requirements.

[Rolls]

Cheers for the data, but if you're mapped for the load/RPM and you have the right AFRs, it doesn't _really_ matter whether the injector is open for 100%, 90%, or 20% - it's still correctly-mapped.

Yes this is completely true, sorry my point was more that people should realise that above 90-95% they aren't going to get more fuel. The reason I say this is if say you mapped everything at 90% and it is running fine you might go to yourself "Oh I still have 10% to play with so if we get an extra cold day it will be fine" However as seen from the graph it is a false sense of security, you should be treating 90% as the absolute maximum.

As an aside: that graph looks like simple PWM input vs flow output (the ECU's correction for lag time may not be included).

Yes that is all it is, a very simplistic estimated flow vs PWM output. If you know the open and close time for the injector along with the frequency of the PWM signal I could generate an accurate graph for you.

Personally I think the allow 10-20% is a good rule, whilst you may have tuned your car so that it correctly mapped, you still are guessing for changes in boost and air temp. What if you tuned the car in 10c weather and maxed out the injectors? (lets say a very cold day) and then you go out for a drive in the rain in the hills where the air temp is say 4c and the rain on the intercooler causes it to work far more efficiently? You are almost certainly going to need that 10% of headroom.

Edited February 15, 2010 by Rolls