why you should install a higher pressure fpr

[mbtoloczko]

I've been looking doing a bit of research on the fuel delivery rate of our SVXes. Based on what I've found, it looks like the stock fuel system can handle no more than 230 HP without going lean at WOT. The stock injectors are 275 cc/min capacity (at 43 psi), and according to the service manual, the SVX fuel pressure is set to 36 psi at WOT. If I have a jaunt over to this page:

http://www.rceng.com/technical.htm

and in the first worksheet use 230 HP, 6 injectors, a BSFC of 0.5, a duty cycle of 0.8, and a max fuel pressure of 36 PSI, then the worksheet spits out that 277 cc/min fuel injectors are needed for these conditions. That means that any aftermarket mods which improve airflow are going to be pushing the fuel delivery system beyond its limits. This would explain why svxfiles has been seeing improvements in power when he installed a 2000 Legacy 2.5 fuel pressure regulator which is good for 43 psi in his mildly modified SVX. Food for thought folks.

[Trevor]

Worthwhile thoughts and info for sure.

But --- how do I REDUCE the gas my car uses when my wife hacks it about in city traffic etc ? The SVX has proven to be a hungry animal. Even so, it is quite a family pet. :confused: :)

[mbtoloczko]

At less than WOT, the ECU shortens the fuel pulse length to compensate for the higher fuel pressure.

[AFBeefcake]

so if you do any mods you should up the fuel to 43 PSI?

where can i get one and how much?

[Trevor]

Originally posted by mbtoloczko
At less than WOT, the ECU shortens the fuel pulse length to compensate for the higher fuel pressure.

Yes, I am aware of how the ECU functions. I was referring to the hope of improving fuel consumption in respect of an existing car in standard condition, accepting the obvious of having everything in good condition.

Indications are that many desire such improvement. Posting the obvious -- " Keep your foot off the gas ", will earn a booby prize. :rolleyes: :)

[mbtoloczko]

Originally posted by Trevor


Yes, I am aware of how the ECU functions. I was referring to the hope of improving fuel consumption in respect of an existing car in standard condition, accepting the obvious of having everything in good condition.

Indications are that many desire such improvement. Posting the obvious -- " Keep your foot off the gas ", will earn a booby prize. :rolleyes: :)

Ah. I was too focused on the topic. Yeah, its amazing that the car is such a gas guzzler considering that the ECU keeps the a/f mixture right on stoich.

[mbtoloczko]

Originally posted by AFBeefcake
so if you do any mods you should up the fuel to 43 PSI?

where can i get one and how much?

svxfiles said that a fuel pressure regulator from a 2000 Legacy 2.5 is rated at around 45 psi and is a bolt-in replacement. I called up a service shop today to get some info, and indeed that regulator is set to 43 psi. The price is about $70 online. I haven't seen one yet though, so I don't know if its a bolt-in replacement.

[Trevor]

Originally posted by mbtoloczko


Ah. I was too focused on the topic. Yeah, its amazing that the car is such a gas guzzler considering that the ECU keeps the a/f mixture right on stoich.

What puzzles me is that one can doodle about town without exceeding 2200 RPM and the thing still guzzles ! Maybe the AC requires mega HP. :confused:

[immortal_suby]

If that is a bolt in replacement then why do the guys putting turbos in the 2.5RS use an svx FPR? It would seem the legacy unit would be better.

And if this does pan out, don't throw out your old svx fpr - they are very easy to sell -even used- on the impreza forums.


<---- heading over to nasioc tech forums

[AFBeefcake]

any one have a part number for the 2.5 FPR?

[SVXRide]

Mychailo,
Does this mean you're going to be the test mule for this mod? I'm in the middle of drawing up a new air box to allow for a larger drop in filter (stupid ABS keeps getting in the way:D ) so allowing for more fuel flow to go with increased air flow works for me!
-Bill (definitely "keeping his foot off the gas":eek: )

[Phast SVX]

Originally posted by mbtoloczko


Ah. I was too focused on the topic. Yeah, its amazing that the car is such a gas guzzler considering that the ECU keeps the a/f mixture right on stoich.
our car dosnt run stoick, it runs slightly rich, as every car does for safety.

[AFBeefcake]

would some thing like this work

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33553&item=2433517641

they say they have Fuel Rail Adapters for Subaru

[Chicane]

Originally posted by Phast SVX

our car dosnt run stoick, it runs slightly rich, as every car does for safety.

I would say it runs richer than most cars. :| I don't have any evidence for this other than how badly it sucks gas when you're not doing anything. I think in the upper RPMs, it leans out a little, and you're engine is being a lot more efficient. That's just my guess though. I can just sense it with my ESVXP.

- Rob

[AFBeefcake]

or would it be better to go to a juck yard and just buy one off a 2000 2.5 legacy

[immortal_suby]

Everything I have read so far on nasioc suggests the svx fpr is better - less restriction. I am trying to find something supporting going to a regulator from a 2.5 but nothing supports it yet.
still searching....

[immortal_suby]

An interesting argument:

But a fpr does not do jack squat to increase fuel delivery. All it does is adjust what pressure the injectors are seeing at idle, or more vacuum.

A fpr is a diaphragm that is connected on one end to vacuum. The other end has fuel line coming in, also there is a return line going back to the tank.

With a strong vacuum, i.e. idle the diaphragm is being sucked in, this in turn moves a valve that allows more fuel to bypass back to the tank. The result, lower fuel pressure.

When you accelerate, vacuum decreases, diaphragm moves back over, does not allow as much fuel to return to the tank. Result....fuel pressure goes up.

All a fpr does is maintain correct fuel pressure. You don't want an insane amount of back pressure on the injectors. It can cause problems.

An adjustable unit may help in fine tuning an engine.....if you have the necessary modifications.....but the only case you'd need to do that is if you change something in the fuel delivery....ie injectors.

There are rising rate fpr's. These are normally used as a cheaper alternative to buying a bigger fuel pump. They can bump your fuel pressure up....the amount depends on the fpr, i.e. 2:1, 3:1, etc.

if you're insistant on bumping fuel pressure up, despite everything I've just said......I got a simple and cheap (free) mod for ya.

Pull the vacuum line off the fpr. Plug the vacuum line, and put a little rubber nubby over the end of the tube on the fpr.

You'll be running max pressure of the pump all the time.

disclamer: I hold no responsibility for any problems, injurys, deaths, etc you incur if you use the information, despite me warning against it.

Josh

---not my opinion or knowledge, just something to add to this from someone else with experience.

[AFBeefcake]

how would I know if I’m maxxing out my fuel injectors?

if you increase fuel presser the ecu will shorten the injector pulses right?

so if engine needs more fuel would the ecu just lengthen the injector pulses?

[mbtoloczko]

Originally posted by immortal_suby
An interesting argument:

But a fpr does not do jack squat to increase fuel delivery. All it does is adjust what pressure the injectors are seeing at idle, or more vacuum.

...



From what I've read, the vacuum line is used to reduce the fuel pressure at low engine loads. At WOT, it runs at full pressure. Disconnecting it would just make the fpr sit at max pressure all the time and do nothing for the potentially lean condition at WOT.

I don't know why the 2.5 RS turbo people are using SVX fprs. I've had multiple verifications that the 2.5 fpr has a max pressure of 43 psi while the SVX fpr maxes out at 36 psi. Maybe the 2.5 RS people are also installing larger fuel injectors, and in order to have a reasonable injector duty cycle, they need to reduce the fuel pressure??

[mbtoloczko]

Originally posted by AFBeefcake
how would I know if I’m maxxing out my fuel injectors?
===
Install an a/f ratio gauge and watch what happens at WOT. If it goes super lean, then the fuel delivery system is probably being maxed out. This is on my list of things to do in the next week or so.
===

if you increase fuel presser the ecu will shorten the injector pulses right?
===
Yes.
===

so if engine needs more fuel would the ecu just lengthen the injector pulses?
===
Yeah, but the pulse can only be so long. An 80% duty cycle is about the max. The worksheet on the RC Engineering page assumes that the fuel injector is already at an 80% duty cycle (and the fuel pressure is maxed out).

[svxfiles]

mbtoloczko, yes it is a bolt in. two screws, one vacuum line, one fuel line, one small gasoline spill, so dont do it on a hot engine. its on the passenger side, at the end of the fuel rail. twenty minutes, less than a hundred bucks, and the cold engine runs better, the 2500-2800 rpm surge is gone and power seems up over all.

[AFBeefcake]

Would using the 2.5 FPR caused any problems?

[Trevor]

Originally posted by immortal_suby
An interesting argument:

But a fpr does not do jack squat to increase fuel delivery. All it does is adjust what pressure the injectors are seeing at idle, or more vacuum.

A fpr is a diaphragm that is connected on one end to vacuum. The other end has fuel line coming in, also there is a return line going back to the tank.

With a strong vacuum, i.e. idle the diaphragm is being sucked in, this in turn moves a valve that allows more fuel to bypass back to the tank. The result, lower fuel pressure.

When you accelerate, vacuum decreases, diaphragm moves back over, does not allow as much fuel to return to the tank. Result....fuel pressure goes up.

All a fpr does is maintain correct fuel pressure. You don't want an insane amount of back pressure on the injectors. It can cause problems.

An adjustable unit may help in fine tuning an engine.....if you have the necessary modifications.....but the only case you'd need to do that is if you change something in the fuel delivery....ie injectors.

There are rising rate fpr's. These are normally used as a cheaper alternative to buying a bigger fuel pump. They can bump your fuel pressure up....the amount depends on the fpr, i.e. 2:1, 3:1, etc.

if you're insistant on bumping fuel pressure up, despite everything I've just said......I got a simple and cheap (free) mod for ya.

Pull the vacuum line off the fpr. Plug the vacuum line, and put a little rubber nubby over the end of the tube on the fpr.

You'll be running max pressure of the pump all the time.

disclamer: I hold no responsibility for any problems, injurys, deaths, etc you incur if you use the information, despite me warning against it.

Josh

---not my opinion or knowledge, just something to add to this from someone else with experience.

All of the above comments are correct but apparently the issue raised is; how to increase the possible flow rate through existing injectors in order to take advantages of modifications which will increase the output of the engine and therefore demand for fuel.

Increasing the pressure available is an effective method of increasing the rate of flow through any given orifice, in this case injectors. However the rest of the system must be capable of delivering the increased volume. It could be expected that the stock system will have a tolerance and reserve in this respect.

P.S. The sole object of posting the above comment is to simplify, for those not technically inclined, what is disclosed in the formulae included in the interesting data provided by Mychailo.

[Porter]

My SVX runs incredibly rich, especially at wide open throttle. On freeway entrance ramps when I do my customary WOT 2nd->3rd run the smell of rich unburnt fuel is very apparent.

My "duct tape" solution for improving gas mileage and increasing horsepower? Use a simple fuel management tool like an Apexi S-AFC and a wideband A/F sensor and gauge (so you can see the changes in realtime), and pull the A/F ratio back to stoich across the powerband, running a bit richer around the induction crossover point near 4k rpm, and a bit richer towards redline, but far less rich than it does now.

I'd expect this to be good for 5+ hp, and a noticeable reduction in fuel consumption. I have not done this as of yet myself on my SVX, but I have with a number of 2.5 motors, and their behavior with regard to rich fuel delivery is very similar to the SVX. One friend was running extremely rich on a stock 2.5 system with Borla headers, and after tuning some of the fuel out, he jumped from 17 to 24mpg and picked up a noticeable increase in midrange power and off-idle throttle response.

I have an extra S-AFC at the shop, I'll have to do some experimentation with it in the near future and see what kind of results I can get on the dyno.

[Trevor]

The above comments are rather interesting as it is concerted opinion here that all Subarus are hungry when compared with like cars of other makes. I can see no valid reason to run the flat boxer engine any differently to an inline or V configuration. Surely this can not be simply "policy" as sales must be in jeopardy.

Any ideas ?

[Porter]

I agree with what you're saying, Trevor. It does seem strange that they run so rich. Perhaps it's the result of their particular tuning philosophy with regards to building in octane safeguards. I.e., protect from low-octane-induced ping by richening the mixture rather than pulling timing drastically as some other brands tend to do. This is merely conjecture based on trends I have noticed in various stock Subaru timing and fuel maps when playing with ECUtek and other systems. Frankly I don't know why they run so rich, it seems like they could make much more power (or at least improve the abysmal fuel economy!) with a more balanced approach. We need an FHI engineer on this board to sort out these questions for us. :)

[oab_au]

A couple of things here. Since the start of electronic fuel injection, the pressure maintained across the injector nozzle, has been the factory standard of 36 psi. This pressure is maintained by the pressure regulator. As the manifold pressure changes with the throttle opening, the fuel pressure regulator alters the nozzle pressure to stay at 36psi. This means that at idle the Fuel pressure will be about 36psi - 10psi =26psi. at WOT the pressure will be about 36psi - 1psi = 35psi.

The other point is that the ECU uses the Oxygen sensors to correct the air fuel ratio to 14.7:1 only at cruse. At full throttle the amount of fuel injected is set by the data that is written in the ECUs fuel map memory. This ratio would be around 12:1 fuel air for power and is not altered by the Oxygen sensors, which would take too long to react.

Altering the regulator pressure to 43psi would give a 19% increase in fuel at idle and WOT .

Harvey.;)

[want-a-fast-svx]

Out of curiosity then will the HKS Fpr I bought during the engine swap work in conjunction with the stock regulator or am i going to have to disconnect the stock one once i hook the HKS up???Thanks for any info
-derek

[mbtoloczko]

Originally posted by oab_au
A couple of things here. Since the start of electronic fuel injection, the pressure maintained across the injector nozzle, has been the factory standard of 36 psi. This pressure is maintained by the pressure regulator. As the manifold pressure changes with the throttle opening, the fuel pressure regulator alters the nozzle pressure to stay at 36psi. This means that at idle the Fuel pressure will be about 36psi - 10psi =26psi. at WOT the pressure will be about 36psi - 1psi = 35psi.
===
Ah, so that's why the fuel pressure at the injectors is varied; its relative to the manifold pressure. Cool.
===

...

Altering the regulator pressure to 43psi would give a 19% increase in fuel at idle and WOT .
===
According to the RC Engineering website, the increase in fuel delivery is not linearly proportional to the increase in fuel pressure. It goes like the square root of the ratios. So the increase in fuel delivery at WOT would be 100*(sqrt(43/36) - 1) = 9.2%
===

[Trevor]

Originally posted by oab_au
A couple of things here. Since the start of electronic fuel injection, the pressure maintained across the injector nozzle, has been the factory standard of 36 psi. This pressure is maintained by the pressure regulator. As the manifold pressure changes with the throttle opening, the fuel pressure regulator alters the nozzle pressure to stay at 36psi. This means that at idle the Fuel pressure will be about 36psi - 10psi =26psi. at WOT the pressure will be about 36psi - 1psi = 35psi.

The other point is that the ECU uses the Oxygen sensors to correct the air fuel ratio to 14.7:1 only at cruse. At full throttle the amount of fuel injected is set by the data that is written in the ECUs fuel map memory. This ratio would be around 12:1 fuel air for power and is not altered by the Oxygen sensors, which would take too long to react.

Altering the regulator pressure to 43psi would give a 19% increase in fuel at idle and WOT .

Harvey.;)

As I understand it the oxygen sensors provide information the ECU uses at any constant throttle opening. Signals as a result of throttle movements are available to the TCU from the TPS and this is information is used to richen mixture as required for any sudden burst of output.

In the event that mixture was completely tied to the fuel map at WOT surely the system would be rather crude as there would be no adjustment for changes in density of fuel on offer.

Surely at any steady level of throttle opening the mixture will be correctly compensated by the TCU and in the event that a regulator pressure above the original standard is used it could be expected that the injector pulse length would be adjusted accordingly.

N.B. ----- Mychailo has posted earlier in this thread, Ó YESÓ to the question, ÒIf you increase the fuel pressure the ECU will shorten the injector pulses Right ?Ò.

I tend agree with Mychailo and that there would NOT be a 19% increase in FUEL at idle and WOT.

[svx_commuter]

Does a leaner engine run hotter? Maybe that's why FHI likes the rich mix. It would be more reliable?

[mbtoloczko]

Originally posted by immortal_suby
Everything I have read so far on nasioc suggests the svx fpr is better - less restriction. I am trying to find something supporting going to a regulator from a 2.5 but nothing supports it yet.
still searching....

I checked this out on NASIOC, and people use the SVX fpr because it can handle the hi flow rates of large aftermarket fuel pumps. The fprs in the 2.5 machines cannot.

[AFBeefcake]

so what about an aftermarket FPR. Would that be better?

[Porter]

Fuel delivery based on static maps occurs any time the ECM switches into "open-loop" mode. Typically this is on cold start or WOT, though other factors can trigger open loop. "Closed-loop" is when the ECM is actually actively changing fuel delivery based on sensor input, i.e. partial throttle acceleration and other transient conditions. Once you start changing factors like fuel pressure, the difference in run state between open loop and closed loop operation becomes more and more apparent. As the static state ("open loop") fuel delivery is modified, gains (or losses) are seen and realized at WOT, though often not at partial throttle, when the ECM is actively making adjustments to fuel and timing based on sensor input. It can be difficult to sort out a system to behave predictably when saddled with these difficulties. That is why the new generation of ECM reflash services (such as ECUtek) are of such value, they allow reliable and predictable behavior with added power under both open and closed loop conditions. It's unfortunate that the SVX ECM is not supported by the ECUtek system.

[Chicane]

However, you could still get an AEM complete engine management computer and do it with that. Look into it folks.. I'm not going to because I'm po', but if I had money that'd be the way to do it.

- Rob

[mbtoloczko]

I did some reading on the S-AFC. Looks very interesting. If anyone wants to get a better understanding of what this thing does, have a look here:

http://wac.addr.com/auto/obs/safc/safc.html

Porter, have you been able to determine at what throttle position or at what engine loads the SVX switches from closed-loop to open-loop mode?

[svx_commuter]

Originally posted by mbtoloczko


I checked this out on NASIOC, and people use the SVX fpr because it can handle the hi flow rates of large aftermarket fuel pumps. The fprs in the 2.5 machines cannot.

So with the larger fuel pump and the stock 2.5 FPR the fuel rail pressure is too high. Hence the need for the higher flow SVX FPR.

[svx_commuter]

Ques>1
So how does the stock SVX control the WOT a/f mixture?
Ques>2
Does the TPS setting effect the WOT a/f mixture??? Resetting the closed throttle position to a higher or lower voltage.
Ques>3
Can a resistor or something else be added to the O2 sensors to improve gas cruising mileage? Make the ECU think it's rich when it's not.

[mbtoloczko]

Originally posted by svx_commuter


So with the larger fuel pump and the stock 2.5 FPR the fuel rail pressure is too high. Hence the need for the higher flow SVX FPR.

Yes, it seems that the SVX fpr can maintain its design pressure at very high flow rates. The 2.5 fprs create higher pressures than their design pressure. Lots of people where seeing idle pressures of over 50 psi when using a hi flow fuel pump and a stock 2.5 fpr.

[svx_commuter]

Originally posted by mbtoloczko


Yes, it seems that the SVX fpr can maintain its design pressure at very high flow rates. The 2.5 fprs create higher pressures than their design pressure. Lots of people where seeing idle pressures of over 50 psi when using a hi flow fuel pump and a stock 2.5 fpr.

From what was said earlier, about the svx ejector being maxed out, a new larger SVX fuel pump would be required for any turbo or other mod that would require more fuel.

It seems that a differential gauge between the fuel rail and the manifold would be required to sort it all out.

[oab_au]

Originally posted by want-a-fast-svx
Out of curiosity then will the HKS Fpr I bought during the engine swap work in conjunction with the stock regulator or am i going to have to disconnect the stock one once i hook the HKS up???Thanks for any info
-derek

If you are going to fit a better one, then replace the standard one with the new.

Harvey. ;)

[mbtoloczko]

Originally posted by svx_commuter


From what was said earlier, about the svx ejector being maxed out, a new larger SVX fuel pump would be required for any turbo or other mod that would require more fuel.

It seems that a differential gauge between the fuel rail and the manifold would be required to sort it all out.

In the now famous SVX FAQ, the guy says the the SVX fuel pump has more than enough flow to provide enough fuel for a higher horsepower motor, but it would be a good idea to get confirmation on this from least one other source.

[oab_au]

Originally posted by svx_commuter
Does a leaner engine run hotter? Maybe that's why FHI likes the rich mix. It would be more reliable?

Yes John, a lean mixture will run hotter to the point of burning a hole in the piston, which tends to cure the problem.:D

Harvey.;)

[oab_au]

Originally posted by svx_commuter
Ques>1
So how does the stock SVX control the WOT a/f mixture?
Ques>2
Does the TPS setting effect the WOT a/f mixture??? Resetting the closed throttle position to a higher or lower voltage.
Ques>3
Can a resistor or something else be added to the O2 sensors to improve gas cruising mileage? Make the ECU think it's rich when it's not.

Qust1. The WOT mixture is a make up of the base fuel map setting,that is modified by the operational sensors. Battery voltage, air temp, engine temp, Mass Air flow, torque control, etc.

Qust 2. No this signal is secondary to the Mass Air Flow reading. This is the amount of air the cylinder is inducting and sets the amount of fuel injected. The TPS is used mainly for the gear box. Supplies the Throttle pressure.

Qust 3. Yes it could but why?. When cruising the air fuel ratio is as lean as they can get it, around 15:1 Some cars as low as 16:1 using a stratified charge.

Harvey.;)

[Trevor]

Originally posted by oab_au


Qust1. The WOT mixture is a make up of the base fuel map setting,that is modified by the operational sensors. Battery voltage, air temp, engine temp, Mass Air flow, torque control, etc.

Qust 2. No this signal is secondary to the Mass Air Flow reading. This is the amount of air the cylinder is inducting and sets the amount of fuel injected. The TPS is used mainly for the gear box. Supplies the Throttle pressure.

Qust 3. Yes it could but why?. When cruising the air fuel ratio is as lean as they can get it, around 15:1 Some cars as low as 16:1 using a stratified charge.

Harvey.;)

From a previous post queried but without a reply : -

Ò The other point is that the ECU uses the Oxygen sensors to correct the air fuel ratio to 14.7:1 ONLY at cruse. At full throttle the amount of fuel injected is set by the data that is written in the ECUs fuel map memory. This ratio would be around 12:1 fuel air for power and is not altered by the Oxygen sensors, which would take too long to react.

Altering the regulator pressure to 43psi WOULD GIVE A 19% INCREASE IN FUEL AT IDLE AND WOT. Ò

Ò Qust1. The WOT mixture is a make up of the base fuel map setting,that is MODIFIED by the OPERATIONAL SENSORS. Battery voltage, air temp, engine temp, Mass Air flow, torque control, ETC. Ò

The text is quite clear but there appears to be some confusion here.

[AFBeefcake]

Would bigger fuel injectors be a better mod then upping the fuel presser?
Like injectors from a 92 turbo legacy.

[Myxalplyx]

Originally posted by mbtoloczko

and in the first worksheet use 230 HP, 6 injectors, a BSFC of 0.5, a duty cycle of 0.8, and a max fuel pressure of 36 PSI, then the worksheet spits out that 277 cc/min fuel injectors are needed for these conditions. That means that any aftermarket mods which improve airflow are going to be pushing the fuel delivery system beyond its limits. This would explain why svxfiles has been seeing improvements in power when he installed a 2000 Legacy 2.5 fuel pressure regulator which is good for 43 psi in his mildly modified SVX. Food for thought folks.

Hello mbtoloczko,

You calculations seem sound from rceng but I'm commenting on the last part of your post about svxfiles. When you stated svxfiles has been seeing improvements in power when installing the 2000 Legacy 2.5 fuel pressure regulator, were you referring to this thread (http://www.subaru-svx.net/forum/showthread.php?s=&threadid=11789&perpage=15&pagenumber=1) ?
If so, svxfiles didn't provide any 1/4 mile runs, G-tech, or dyno data to support the feeling of more power. The 'butt-dyno' isn't accurate all the time. In fact, power could possibly be being lost rather than gained, like running higher octane can increase throttle response in some cars but the car actually lose hp/torque (XT6 for instance in my case).

A dyno plot or some 1/4 mile runs with before and after comparisons should put some of the assumptions to rest. Also, has anyone actually hooked up an air/fuel ratio and/or EGT (Exhaust Gas Temperature) gauge up to monitor just how rich or lean their SVX is running yet? I've read about Porter being interested in it but nothing concrete. I could've just over-read it somewhere in this thread or another one.

It just seems that most people are assuming more power is to be had with increased fuel pressure without proof although the calculations seem sound.

[AFBeefcake]

I have a air/fuel gauge in my car.
I never have had my gauge go more then 3 bars to the rich side.

[svxfiles]

i use a marked streach of road, drive at exactly 25 mph,ac off, windows and stereo off, when i get to the 50 mph sign i drop the hammer, wide open throttle. i hold it down until i go past the speed zone ahead sign on the opposite side of the narrow 2 lane road. this is how i can say there has been some improvement or not.

[mbtoloczko]

No one seems to have tested it on a dyno or on the track, but svxfiles' approach seems to be reasonable. I've got an a/f meter sitting on the table next to me. I plan to install it as soon as I figure out the ECU lead wire for the O2 sensor on the side of the motor that is furthest downstream from the fuel pump.

Hey svxfiles, what brand and model of adjustable fpr are you using? What it much work to install it?

[Szalkerous]

with all this talk and hashing out, it almost seems like a worthwhile venture to make this fuel delivery discussion an open source project....

can we reasonably combine resources to provide us with an accurate aftermarket setup to support higher HP? Aftermarket pump, FPR, injectors? Can we put together a system that we know works with p/n's? Anyone wanna try to research available options?

Fuel delivery is a good starting place for creating and balancing a higher-HP H-6.

I suggest to those interested we...

1. Research and crunch numbers to justify the requirements and potential of the aftermarket setup (MSD has a good array of resources including injector matching software at http://www.msdignition.com/fuel_intro.htm )

2. Check resources to find available parts options, be it aftermarket companies or parts swaps from other cars.

3. Combine it as a potential kit?

I would love to have a known setup that has been agreed upon by the various minds here that we can apply to our cars :D

(This could also be a base accomplishment for other projects down the road, such as a potential TT setup....???)

-Sz

[mbtoloczko]

Check out this thread for another possible reason why svxfiles is seeing better performance with a higher pressure fpr:

http://www.subaru-svx.net/forum/showthread.php?threadid=13612

Read up to at least this post:

http://www.subaru-svx.net/forum/showthread.php?threadid=13612#post149184

[BackWoodsBob]

So, is the FPR from a 2.5 a good choice to raise the fuel rail pressure at WOT to bring the a/f below 14.5 and keep the power going?

Bottom line here, I've read this thread, but it seems to be going back and forth. Who has done this mod, recorded data, and can say one way or another that the engine runs better or not?

I have a CAI with a 4in primary splitter at the throttle body with a 3" duct to the fender. I imagine I'm on the lean side of things?

[SVXRide]

Bob,

A lot of folks are running the higher pressure fpr. Easy to install. I'd only recommend it if you aren't going to run one of LAN's ECUtune chips.

Bill

[svxfiles]

Bob,

A lot of folks are running the higher pressure fpr. Easy to install. I'd only recommend it if you aren't going to run one of LAN's ECUtune chips.

Bill
LANs chip does a better job than the higher pressure FPR.

However LANs chip will work with the higher pressure FPR as well.;)

[Huskymaniac]

Am I calculating this correctly...stock injectors with the higher pressure fpr will deliver up to about 275HP worth of fuel.

[svxfiles]

Am I calculating this correctly...stock injectors with the higher pressure fpr will deliver up to about 275HP worth of fuel.

Thats pretty close to what I have found.

What are you using for B.S.F.C.?

[Huskymaniac]

Thats pretty close to what I have found.

What are you using for B.S.F.C.?

What is B.S.F.C.?

[svxfiles]

Brake
Specific
Fuel
Consumption

From Wikipedia, the free encyclopedia
Brake Specific Fuel Consumption (BSFC) is a measure of fuel efficiency within a shaft reciprocating engine. It is the rate of fuel consumption divided by the power produced. It may also be thought of as power-specific fuel consumption, for this reason. BSFC allows the fuel efficiency of different reciprocating engines to be directly compared.

[BackWoodsBob]

Bob,

A lot of folks are running the higher pressure fpr. Easy to install. I'd only recommend it if you aren't going to run one of LAN's ECUtune chips.

Bill

Thank you Bill. I did what I had to during my engine swap, and didn't realize how starved the EG was already. :lol: oops. So now I have a super free flowing EG, that doesn't pull in the upper RPM's.

I have a line on a used FPR from an 01 impreza, going to install that and see how things go. Eventually I plan on a mild boost 5-8psi with stock internals so I'll be running ECUtunes stage 2 chip with the 2 map jumper.

LANs chip does a better job than the higher pressure FPR.

However LANs chip will work with the higher pressure FPR as well.;)

Didn't know that, thank you much!