rising rate fuel regulator-tuning-basics?

[petespipes]

Yep,checked FAQ
Yep.searched rrfr.
thanks for asking.........OK.I am about to install a basic rising rate fuel regulator that is 1:1 which means it will add 1 pound of fuel pressure for each pound of boost it measures at the
inlet manifold.

This type of mod is a cheap fix for those in the situation of having a desire for more power and requiring more fuel to get it while being near or at 100% duty cycle on their injectors.While it is a cheap fix it is not an ideal fix as the way it works is apparently far from perfect and that is the reason for the post.[more info required]

So the idea is to gain the required extra fuel to enable a retune for more power via higher boost etc by simply upping the fuel pressure.[rather than fitting larger injectors]

The tool required to up the fuel pressure is a Rising Rate Fuel Pressure Regulator.I purchased a baby Sard useful up to 450hp [standard item] worth approx $150

So,provided my fuel pump is up to the job [for the purpose of this exercise we will assume all fuel pressure requirements are met]

OK.assuming base fuel pressure on this 1j cressida is 30psi and we are going to run 20psi boost which will mean the Sard rrfreg will up the fuel pressure to 50 psi .[30psi plus a 1:1 rate of one lb of fuel pressure for each pound of boost = 50lb]

To gain the increase in fuel flow percentage its necessary to use the following equation-
new fuel pressure
----------------------------x old fuel flow = new fuel flow
old fuel pressure

or 50 over 30 x 100 = 129 which is roughly a 20% increase in fuel which should allow a 20% increase in power to my simple brain.[thanks to GT,cambelt,pure_in_sanity]

OK,so again for the purpose of the exercise and allowing me to get to the nitty gritty of where i want to go with this please assume we had 300 rwhp and we want 360rwhp therfore we did the aforementioned mods to gain extra 20% fuel

Here is the catch.All the boost gain occurs between 3000 and 4000rpm so all the fuel pressure increase happens here also.Obviously the fuel requirements increase with revs,NOT with boost.

So,does this mean the engine will run rich at 4000 and progressivel lean out towards 6000rpm or what? given the fact that fuel pressure will remain constant from 4000rpm but fuel flow will need to increase markedly towards higher revs to maintain A\F ratio

my apologies for lack of keyboard skills but hoping you can follow my drift.reason for wanting to stay with existing injectors and management is to simply put as cap on costs of this car as its already well over budget and a new project awaits.

cheers for any assistance in understanding what happens with this type of tune.

[oldcorollas]

aren't normal fuel pressure regulators 1:1 ratio.. ie, not rising rate??

this is usually done so that thepressure differential across the injectors remains the same..

rising rate is like 1.5psi per pound boost, or whatever..

i'm not sure i follow you with the fuel/revs argument?

usually, the rail pressur eis 40psi over manifold, and a rising rate will increas say (for example) 1.5psi per boost, so 20psi boost = 40+30psi = 70psi..

the main danger with running a RRFPR is that most fuel pumps start to flow poorly over 60psi or so...
there are published flow charts for at least the walbros and the bosch pumps...

so as you up the boost, you start losing fuel flow, cos you are asking it to supply at a higher pressure (and can have dangerous sudden leaning up top)

fuel requirement increases with air, ie, both boost and rpm....

with a RRFPR, usually what would happen (without other mods) is that with increasing boost, you run richer and richer...until the pump can't produce flow at that pressure and it all goes bang

[Hen]

OC, I thought that a RRFPR labelled as 1.5psi fuel / psi boost will increase absolute fuel pressure by 1.5psi per 1psi of boost. So the differential across the injector will increase by only 0.5psi.

So in the above equation, if you have 40psi differential across the injector under vacuum, then at 10psi boost it should rise to 45psi differential (55psi absolute) and at 20psi boost should be 50psi differential (70psi absolute).

Also as far as I know (may pay to check) injector flow increases with the square root of fuel pressure. So a 21% increase in pressure will only increase injector flow by 10% since 1.10 = sqrt(1.21).

Hen

[MS-75]

Also as far as I know (may pay to check) injector flow increases with the square root of fuel pressure. So a 21% increase in pressure will only increase injector flow by 10% since 1.10 = sqrt(1.21).

Hen

Correctamundo.

[chris davey]

I have noticed tuning that you need the most amount of fuel at the peak torque figure (while mainting a constant AFR) ie. me running 14psi the most amount of fuel is injected at around 5000rpm even though I rev it to 7500rpm.

So if you have full boost at 4000rpm, then you will probably have to have your maximum % correction at around 5000rpm like me and then drop a bit out up top.

Also agree that a 1:1 won't actually do anything different to your stock one. The 1:1's are mainly used for people converter from n/a to turbo. That is why I haven't really bothered installing mine.

Have to ask though, for the price of some 440cc injectors from a 2jz is it worth it?

Oh, I was also told by a knowledgable fellow that increasing the rail pressure on a fuel rail with side feed injectors isn't a good idea as it can push the o-rings out a bit and make them leak.

On the other hand, SICO1J used to run 60psi base pressure in his car. I wouldn't be doing it that way but it did "seem" to work.

[oldcorollas]

OC, I thought that a RRFPR labelled as 1.5psi fuel / psi boost will increase absolute fuel pressure by 1.5psi per 1psi of boost. So the differential across the injector will increase by only 0.5psi.

So in the above equation, if you have 40psi differential across the injector under vacuum, then at 10psi boost it should rise to 45psi differential (55psi absolute) and at 20psi boost should be 50psi differential (70psi absolute).

hmmm, i was thinking 1.5 ratio, but types 1.5psi/boost
wait.. i think we are saying same thing

40psi stock differential. 1.5 ratio (1.5psi/boost) RRFPR, 20psi boost.
normally, you have fuel rail pressure of 60psi, and differential of 40psi.

with RRFPR, you have 70psi rail pressure, but as you say differential of 50psi, so the increase is only 10psi the injector sees.

i just said it badly as i was trying to highlight the prob with the increased rail pressure

and that a 1:1 FPR is not rising rate..... (cos the rate of increase is not rising???)

as example below, it's all well and good to increase your fuel rail pressure to increase the diffeerential across injector.. but at some point, you will run out of fuel the pump can provide, ie normal walbro 255 flows HALF at 80psi what it does at 60psi.... seems like a baad idea..

[Draven]

ok, can I ask a really stupid question, because I have only a very vague idea on how a fuel pressure regulator works...

I'm planning on running ~24psi of boost, and for some reason I thought buying a sard FPR would be a good idea to aid this end, ditching the stock JZA80 one. Considering I'm running aftermarket management and big injectors, is the sard regulator even needed, or would the JZA80 one be good enough?

[oldcorollas]

fuel comes in the bottom, pushes up the diaphragm, and then "leaks out" thru the middle tube.
the spring on top pushes down the diaphragm and sets the pressure the fuel has to overcome to push the diaphragm out of the way to escape.

boost reference is also on the right, above the diaphragm...
with vacuum, it is pulled up, and with boost, it is pushed down, thus changing the pressure the fuel has to reach to escape.

another crappy pic.. looking for RRFPR pic now
hmm, the differenc with RRFPR, is that the area acted on by the boost pressure, is larger than the area acted on by the fuel (or some similar setup), such that you need more fuel pressure acting on a smaller area, to counter the boost pressure acting on larger area..
(alhtough i am not sure on the internals of all the different types available)

[thechuckster]

fwiw: i'm finding that tuning my fuel map with a RRFPR is proving to be difficult - there's so much fuel being dumped into the engine that it missfires resulting in lean signals from the WB02 (when infact it's an AFR of something around 10:1) ... and once you get over the missfire signals, you still have a VE table (MAP-versus-RPM) that looks almost flat once it's over 100kpa of MAP (e.g. 0psi boost).

In some respects, when deciding to use a RRFPR i should have re-thought my injector selection (4agze units) and used something smaller (around 280-290cc/min instead of 365 cc/min) as during boost, minor changes in VE values in my fuel map result in major changes to fuel delivery.

If i found a reasonably priced aeromotive or sard unit that i can bolt to the firewall, i'd change to it.

[Draven]

http://www.nengun.com/sard/fuel-regulator-8mm-nipple

I just realised the SARD I bought is not a rising rate, it's designed to maintain fuel pressure at high boost (so I assume it's a 1:1), which is a good thing

[Norbie]

Yeah you only need a RRFPR if you can't tune the fuel maps, ie stock ECU. With proper management you want to stick with a normal 1:1 FPR as found in every factory EFI engine, turbo or not.

The SARD FPR is obviously designed for high fuel flow, ie the stock FPR may be too restrictive when you're using a big fuel pump which can lead to high fuel pressure at low load, exactly when you don't want it!

[petespipes]

Hmmmm,a bit to digest here.Nice.Didnt expect so much info so fast.Awesome.

Tuners are so busy and have to deal with so many wankers that they tell you whatever they think you want to hear.Or so it seems to me.

Thanks to all,may PM for clarification once i get time to get my head around some of this.

Yeah the reason for not simply upping the injectors is that im running safc2 and im informed it wont run bigger injectors succesfully.If the rrfpr is not the answer its possible i could use my emanage and 550's on this engine but i was after a cheap fix.I thought more fuel pressure and up the boost with a tune to suit and voila.More power cheap.

I have a new project so the Cressida is near finished but the GT3076 has plenty in it that im not using so thats why im trying to get some fuel happening.

[oldcorollas]

why wouldn't bigger injectors work? i thought the whole point of an SAFC was to reduce the pulsewidths so you can use bigger injectors....

[petespipes]

true,and all the blurb clearly states that you can run bigger injectors with this device.BUT i have been unable to find a person actually running safc2 with larger injectors who has a clean idle.Have had one or two come forward with idle problems on 440's from memory and actually purchased and resold 440's because of this.
`thanks for your input,please keep up the suggestions.

[oldcorollas]

well..
SAFC is basically an interceptor right?
so all you are doing is changing the inputs to the stock ECU, and then hoping you get the right pulsewidth out of it.

idle will have about the lowest pulsewidth available (except for maybe cruise at low rpm), so the minimum pulsewidth is kind of set by the stock ECU.

what i mean is...
say you have 25% bigger injectors (550/440)... that measn for the same stock ECU, you have roughly 25% more flow everywhere.
up top, this is fine, cos maybe that is how much you want, but as you go lower in rpm/load, you need to decrease the "effective load" the ECU sees (with the SAFC) so that it reduces pulsewidths....

BUT.. there is a limit. at the stock ECU's minimum pulsewidth, you can't change the effective load to read any lower.

so what you might need to do (and i see this with a few cars around here) is to up the idle speed, to a point where you can reduce the pulsewidth more.. ie 1200 or 1500 or whatever..

so basically, at idle speed, the ECU sets minimum pulsewidth. without knowing the stock mapping in that area, reducing the MAP/AFM effective load may not actually reduce pulsewidth any more.

ideally, you would make up a test circuit to simulate the engine, and then map out the PW's for the stock ECU to see what is happening...

also, by reducing the load too much, you might change the spark advance response of the ECU, cos it goes into recover idle mode or something...

anyway, thats my thoughts... you have 1 black box, and another you are hoping to use to change the black box output. measure the black bo and it will all be clearer

edit... how about reducing the fuel pressure at idle.. from say 40psi to 35 or 30psi
worse atomisation, but reduces the actual flow... will reduce the flow up high also, but with the extra from boost compensation (at 1:1) you might just achieve both goals.