why you should install a higher pressure fpr - Page 4

AFBeefcake · #46 10-05-2003, 11:30 AM

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

Myxalplyx · #47 10-06-2003, 06:50 AM

Quote:

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 ?
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 · #48 10-06-2003, 07:08 AM

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 · #49 10-06-2003, 07:29 AM

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 · #50 10-06-2003, 09:09 AM

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 · #51 10-08-2003, 10:32 AM

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

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

-Sz

mbtoloczko · #52 10-08-2003, 12:36 PM

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/show...threadid=13612

Read up to at least this post:

http://www.subaru-svx.net/forum/show...612#post149184

BackWoodsBob · #53 09-25-2012, 12:16 PM

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 · #54 09-25-2012, 12:21 PM

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 · #55 09-25-2012, 12:56 PM

Quote:

Originally Posted by 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

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

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

Huskymaniac · #56 09-25-2012, 01:39 PM

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

svxfiles · #57 09-25-2012, 04:39 PM

Quote:

Originally Posted by Huskymaniac

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 · #58 09-25-2012, 06:43 PM

Quote:

Originally Posted by svxfiles

Thats pretty close to what I have found.

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

What is B.S.F.C.?

svxfiles · #59 09-25-2012, 07:06 PM

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 · #60 09-26-2012, 10:16 AM

Quote:

Originally Posted by 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

Thank you Bill. I did what I had to during my engine swap, and didn't realize how starved the EG was already.

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.

Quote:

Originally Posted by svxfiles

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!