Adjustable RR-FPR ratings and using an aftermarket ecu

[77magnum13hundy]

OK not too sure about Fuel Pressure Regulators, especially this rising rate one i got.

The guy told me it was 1 : 1 which means 1 part air to one part fuel adjustments when rising.

The receipt says 1.25 : 1 which makes me think thats guna be leaner than normal) not sure if this will cause problems along the line. Maybe too much air to fuel Lean it out too much

The guy says it would be fine for under 10 psi boost status's. If i run a custom map to have "x" amount of fuel at this time at this load etc does the RR FPR even come into play any more? As it would adjust the flow of gas to suit the conditions as the ECU is telling the injectors how long to be on for...

Anyone toy'd with this idea, if i set this to be standard fuel pressure, and just let it add more gas, and drop off the amount the ecu sends in fractionally will i have some form of sweet mixture to drive it with.

So what im really asking is... Does the RR FPR become obselete in such a situation or can it give a little more gas when needed when on boost?

[Rookie]

The reason you use a boost referenced (1:1) or Rising Rate (anything more than 1:1) FPR is so that as you add boost the fuel pressure doesn't "appear" to be decreasing.

As you add boost the pressure differential across the injector gets less, so say you had a base FP of 43 psi and 10 psi of boost, your injectors will see a pressure differential of 33 psi. so what a boost referenced FPR does is adds 1 psi of FP for every 1 psi of boost, so when you are on boost your injectors will still see 43 psi of FP.

Similarly a Rising Rate FPR will add (in your case) 1.25 psi of FP for every 1 psi of boost, so your injectors will see a differential of 45.5 psi and hence will flow more when on boost. Rising rate FPR are kind of a work around for not having big enough injectors, or using the stock ECU with extra boost, they can be used to good effect with a custom tune though, so don't count them out for that either.

[kpr]

fake edit: too slow

use the factory regulator. they are far more reliable than most aftermarket stuff. even some of the more expensive ones drop pressure over time. cheap ones are total rubbish.

1:1 reg is usually what factory runs, so the fuel pressure isnt offset by manifold pressure.

1.25:1 is more aggressive, so will give you more fuel under boost. generally used if injectors are too small or your trying to add more fuel on a standard ecu

doesn't matter what you run with aftermarket ecu, as you can tune around it.. but the best way is to stick with the factory 1:1 reg and run larger injectors if more fuel is require. less to go wrong, more reliable

[durty]

Bit of a noob here.

But does that mean you could theoretically use a rrfpr on a standard ecu/non turbo car that is +T and it would have less chance of blowing up? What about with bigger injectors?

[kpr]

in theory yeh. but is pretty dodgy for a few reasons,

no igntion retard for boost

most n/a ecu's will shutdown if they see boost, can add a fcd to remove the cutout.

if running very small amount of boost it can work. or same deal for turbo car thats hitting boost cut. use a fcd and a rising rate reg to add more fuel after where the cut out would be.

bigger injectors on factory ecu isnt good, will just make situation worse. will run rich off boost

can run add on fuel controllers and shit to trim the fuel. but by the time you buy all that stuff. far better off to run an aftermarket ecu

[durty]

Sweet as. Cheers for the info. Just means I need to be bothered installing the other ecu I have. Just hate wiring.

I have the ecu and loom from the turbo version of my engine so will just install that to be safe

[Stu]

+1 for stock reg.

If you really want you can add an adjustable reg into the return line from the rail (after stock reg), this way if your running a stock ecu the low load/idle maps will be as per factory and the extra fuel will only come in when your seeing boost. But if your running an aftermarket ecu just run the stock reg and tune to suit.

Adj regs can vary a bit over time too so it pays to keep an eye that they're still set the same.

Aftermarket ecu best, don't need adjustable reg, just tune to suit.

If 4afe/ge cough* 4efte map sensor and injectors on stock ecu *cough

[77magnum13hundy]

OK got a link now, so can set up the fuel map.

About the Stock regulator, how will it preform when it see's boost? Will it push the diaphram fully open thus closing the return path more(or vice versa whichever way they work), or will it have the opposite affect and will close the diaphram resulting in fuel running back out the return.

Do I set it up at just 43psi and have no vaccuum hose connected? Then its just up to setting how long the injectors stay on for fuel wise.

[Stu]

I always had mine plumbed up as per standard with the vac line.

Pretty sure the boost signal pushes down on the diaphram keeping it closed increasing rail pressure.

[77magnum13hundy]

ok so where i had my cold start injector pipe running(4age) off the rail, il put the pressure gauge in there and put the normal fpr in and then at least i can see what psi is running at what rpm. Cheers for the insightfull info...

[Yowzer]

I was reading awhile ago on some Supra forum about guys who turbo their 5MGEs, they slap 12:1 RRFPRs on them and some weird piggyback fuel controller to tweak the fueling, so they can make 400hp on factory 172cc injectors and stock ECU.

I thought that was fucking stupid.

The factory FPR should be more than mint up to 10 odd PSI, after that they can get a bit sketchy as they were never designed to take that much positive pressure, unless you raid one from a factory turbo car.

In any case, if you have an aftermarket ECU and injectors that can flow enough fuel to match your power output, a 1:1 or thereabouts is perfectly lush. The only reason you ramp the fuel pressure up more is because you are too cheap to buy better injectors.

[kpr]

they are fine for plenty of boost. works similar to an external wastegate. adding more pressure to the top of the diaphragm, effectively increases your spring pressure. so your base 43 psi spring plus 10psi pressure, now requires 53psi fuel pressure before it will bypass down the return line. both stu^ and i have used the stock 4age regs with near 20psi boost pressure. i even put a 20v 4age one on a rb30det skyline the other day, as the nissan one shat itself..