Fuel Pressure

[svxfiles]

mbtoloczko,#22670aa221 is the part # for a 2000 2.5 with manual transmission. please check a subaru shop manual to be sure the pressure is 45.4 or so.
want-a-fast-svx, i have a similar set up on my 92, hooked into the return line on the drivers side intake manifold, im not going to do this to my sons svx, or my girlfriends svx, because their cars will have very few engine mods. k+n drop in air filter, better flowing exhaust system. unless you turbo or supercharge,there is no need for bigger fuel injectors. but venom has some that flow 10% more than stock for $43.3 each thru NOPI
phast svx, you are right saying more fuel does not equal more power,but,if they have modified their svx with a drop in filter, or a cone filter, or an intake tube, or changed the exhaust with something free flowing then their cars will benefit from a f/p increase. i do have a road that i allways run to see if my modification have helped or hurt. for instance, running over 48psi on my car does not make it any faster, but at least i have the option of up or down for later

[mbtoloczko]

Originally posted by Phast SVX
you cant make power from nothing. Just adding an FPR will not do anything, i can garuntee it. You may think youfeel something from it but you cant dump more fuel in and expect to have more power. You have to be able to add air, then add fuel. Remeber fuel is added according to the amount of AIR that is being put into the the engine, not vice versa.
phil

I was thinking the same thing. I asked, and he answered. See above. The answer seems reasonable to me. I doubt there will be much of a HP gain, but it sounds interesting.

[mbtoloczko]

Originally posted by svxfiles
mbtoloczko,#22670aa221 is the part # for a 2000 2.5 with manual transmission. please check a subaru shop manual to be sure the pressure is 45.4 or so.

Thanks!

[elninoalex]

I thought that raising the fuel pressure slightly, to help simple intake and exhaust mods, only helps on a speed air density type of intake and not on mass airflow. On mass airflow, the MAF sensor reads the amount of airflow and adjusts fuel accordingly. Speed air density works off of a map and has to be remapped, or have the fuel pressure raised to compensate for increased airflow. At least that is what I remember reading in my textbook.

Stephen

[Phast SVX]

that is my undrestanding as well, i dont think you will gain anything at all
phil

[svxfiles]

eleninoalex, yes, a mass air flow adjusts the fuel injection to suit the air flow, but with anything, there are limits. since i didnt want to spend the money for bigger fuel injectors if i diddnt have to, this method will allow the injectors to preform like bigger jets when called upon. check out the other import racers. or try it yourself

[elninoalex]

I have read that Infiniti Q45 injectors are a bolt in replacement.
How much more fuel are you needing to flow? I have run 100 hp more than stock with a dry nitrous system realizing all of the power. Of course that's once in awhile, but I still don't think the stock injectors get the credit they deserve.

Stephen

[mbtoloczko]

Originally posted by svxfiles
eleninoalex, yes, a mass air flow adjusts the fuel injection to suit the air flow, but with anything, there are limits. since i didnt want to spend the money for bigger fuel injectors if i diddnt have to, this method will allow the injectors to preform like bigger jets when called upon. check out the other import racers. or try it yourself

So now I'm curious; do both the signal from the MAF and the signal from the O2 sensors control the amount of fuel dumped into the engine?

I just thought I'd mention that svxfiles theory behind improved performance has nothing to do with air/fuel ratio. Its just better atomization through higher fuel pressure.

[svxfiles]

mbtoloczko, yes, the maf tells the computer how much air the engine is using, and the o2 sensor tries to heep it at an efficiently lean ratio. but at wide open throttle the o2 is out of the loop, if its been modded for improved air flow then it will run leaner. since i installed my adjustable fpr ive learned from consistant speed runs, that is slower at 37psi than 42psi, and fastest at 48psi with my set up. ie headers, true duals, cone k+n inside the right fender, maf relocated to the right inner fender, tripple gaskets between the upper manifold and the lower,etc.

[want-a-fast-svx]

Svxfiles, where did you get your header made at???and how much was it??if you dont mind me asking...Also what did the triple gaskets do inbetween the upper and lower intake manifold???Thanks for any and all help...

[svxfiles]

want-a-fast-svx, i fabricated the headers myself, with our shop tubing bender, it took probably 30 hours and $100.00 for aluminized 1.5 id tubing, and $20.00 for 1/4 plate. the theory behind the tripple gaskets is to lessen the heat transfer from the engine into the upper manifold.

[mbtoloczko]

Originally posted by svxfiles
want-a-fast-svx, i fabricated the headers myself, with our shop tubing bender, it took probably 30 hours and $100.00 for aluminized 1.5 id tubing, and $20.00 for 1/4 plate. the theory behind the tripple gaskets is to lessen the heat transfer from the engine into the upper manifold.

Any increase in performance with the headers? Do the headers have equal length pipes to the collector? What is the distance from the manifold to the collector? Did you pick a particular distance based on desired peak torque/HP location in the powerband?

[svxfiles]

mbtoloczko, it does pull harder from 4500 rpm on, but below that its about the same ( mabey less ) this was my first set of self fabricated headers, so i was more concerned with ground clearance than equal length. 30 to44 inches using the old school log type hot rodders used in the 50s. if i make another set, it will be 1.5 id x 40.42 ( or as close as i can get )with a 2.5 collector for non supercharged or non nitrous. if i can ever go with a supercharger or dicide to go with nitrous, then id use 1.75 id x 29 inches with a 2.75 collector. i got my new specs using racers math

[mbtoloczko]

Originally posted by svxfiles
mbtoloczko,#22670aa221 is the part # for a 2000 2.5 with manual transmission. please check a subaru shop manual to be sure the pressure is 45.4 or so.
...

For anyone still following this thread, the correct part number for an fpr for a 2000 Impreza RS 2.5L is 22670AA240. The 221 fpr is for the 2.2L motor.

[svx_commuter]

I hope it's okay with everyone to have a link here to a MOD Mania thread on the fpr and a/f thread. It just sort of ties things together.