Jump to content


Welcome to Ultimate Subaru Message Board, my lurker friend!

Welcome to Ultimate Subaru Message Board, an unparalleled Subaru community full of the greatest Subaru gurus and modders on the planet! We offer technical information and discussion about all things Subaru, the best and most popular all wheel drive vehicles ever created.

We offer all this information for free to everyone, even lurkers like you! All we ask in return is that you sign up and give back some of what you get out - without our awesome registered users none of this would be possible! Plus, you get way more great stuff as a member! Lurk to lose, participate to WIN*!
  • Say hello and join the conversation
  • Subscribe to topics and forums to get automatic updates
  • Get your own profile and make new friends
  • Classifieds with all sorts of Subaru goodies
  • Photo hosting in our gallery
  • Meet other cool people with cool cars
Seriously, what are you waiting for? Make your life more fulfilling and join today! You and your Subaru won't regret it, we guarantee** it.

* The joy of participation and being generally awesome constitutes winning
** Not an actual guarantee, but seriously, you probably won't regret it!

Serving the Subaru Community since May 18th, 1998!

Guest Message by DevFuse
 

Photo
- - - - -

How to increase fuel pressure?


  • Please log in to reply
36 replies to this topic

#1 whiplash-smile

whiplash-smile

    USMB Regular

  • Members
  • PipPipPip
  • 35 posts
  • Colorado

Posted 10 November 2003 - 09:31 PM

I have a 1988 turbo fulltime 4 wheel drive with the 4 speed auto. I would like to increase my fuel pressure to my injectors. Can someone save me from reinventing the wheel?

#2 calebz

calebz

    Andys Coupe killed my cat

  • Administrator
  • 7,547 posts
  • Tacoma

Posted 10 November 2003 - 09:37 PM

You can increase the fuel pressure to your injectors all you want.. Thats easily acomplished by removal of FPR and/or installation of a higher output pump. But the injectors themselves are limited to how much fuel they can spray with each pulse.. If your goal is to raise the amount of fuel your injectors are putting out, its time to hunt for larger injectors.. maybe injectors off an older Z-car?.. seems I heard somewhere that they might work.

Are you running higher than stock boost?

#3 whiplash-smile

whiplash-smile

    USMB Regular

  • Members
  • PipPipPip
  • 35 posts
  • Colorado

Posted 10 November 2003 - 10:00 PM

Originally posted by calebz
You can increase the fuel pressure to your injectors all you want.. Thats easily acomplished by removal of FPR and/or installation of a higher output pump. But the injectors themselves are limited to how much fuel they can spray with each pulse.. If your goal is to raise the amount of fuel your injectors are putting out, its time to hunt for larger injectors.. maybe injectors off an older Z-car?.. seems I heard somewhere that they might work.

Are you running higher than stock boost?



Thanks for the response! But... It sounds like you think that if our stock fuel pressure to the injector is 25 psi, and we double it(for arguments sake) and the bandwidth of each pulse stays the same, that more fuel won't be discharged from the pintle on each pulse?
Most car manufacturers size their injectors to a certain percentage of the maxium duty cycle for the size of a motor and its volumetric efficiency. Typically 60-80%, I am hoping Subaru's engineers think similarly to other M.E.'s.
Can we adjust our FPR's?
And yes I have increased my boost.

#4 electryc_monk

electryc_monk

    Air-ride Airehead

  • Members
  • 1,581 posts
  • Denton, Tx

Posted 10 November 2003 - 10:49 PM

a newbie to the board with some mechnaical errm, electrical mechanical knowledge.

For the record so your up to speed, ummm we have a few folks that are already aware of this which your speaking and that they are / were trying to squeek a few more PSI or converting to the higher non EA82 turbo fuel pumps.

SPFI and MPFI non-turbo PSI is about 35-40 PSI
Turbo MPFI is a whopping 67 PSI IIRC.


now on to more fun...

again welcome dude.

#5 calebz

calebz

    Andys Coupe killed my cat

  • Administrator
  • 7,547 posts
  • Tacoma

Posted 10 November 2003 - 11:27 PM

Originally posted by whiplash-smile
Thanks for the response! But... It sounds like you think that if our stock fuel pressure to the injector is 25 psi, and we double it(for arguments sake) and the bandwidth of each pulse stays the same, that more fuel won't be discharged from the pintle on each pulse?
Most car manufacturers size their injectors to a certain percentage of the maxium duty cycle for the size of a motor and its volumetric efficiency. Typically 60-80%, I am hoping Subaru's engineers think similarly to other M.E.'s.
Can we adjust our FPR's?
And yes I have increased my boost.



I believe that the Fuel pressure going in to the fuel rail is right around 35-37 PSI. My Factory Service Manuals are out on loan at the moment, so I can't look that up. The FPR in our cars isn't adjustable to my knowledge, but installing an adjustable FPR wouldn't be any problem I wouldn't think. However the fuel system is built with a return line, and if my understanding of its operation is correct, any fuel above the injectors pressure rating is sent back to the tank via that return line. If your idea holds true, and we can increase fuel pressure 20-40%, that could be very helpful at higher boost levels. Would running the injectors at/near maximum possible output all the time shorten their lifespan? Its possible that the pulse pressures are limited by the ECU, inwhich case an aftermarket fuel management system would be the way to go.

Perhaps Skip could chime in with some info here. I know he has a better understanding of the fuel system than I do.

How high is your boost?
Are you running an Intercooler?

Oh yeah, and welcome to the board
:D

#6 Do It Sidewayz

Do It Sidewayz

    Subaru Fanatic!

  • Members
  • 464 posts
  • Toronto, Ontario

Posted 11 November 2003 - 01:45 AM

you can actually make your own adjustable fuel pressure regulator. You just need to modify the stock one.

What you do is remove it from the car.

Drill a 1/4 inch whole int he top

Solder/braze on a 1/4 nut inline with the hole

screw in a bolt

Install a fuel pressure gauge

and screw in the bolt until you get the pressure you want, then lock the bolt with another nut.

We have done this to ALL of our EA82T race car motors. You do get more fuel into the combustion chamber, because for the same pulse, more fuel is forced through the injector.

I have a feeling we are running about 45-50 PSI now.

#7 electryc_monk

electryc_monk

    Air-ride Airehead

  • Members
  • 1,581 posts
  • Denton, Tx

Posted 11 November 2003 - 02:31 AM

and picture and written data documentation would be supremely benefitial and worthwhil sticking in the USRM too!

#8 Free Range

Free Range

    Chicken or the egg, hmm?

  • Members
  • 215 posts
  • Missoula, MT

Posted 11 November 2003 - 12:39 PM

I'm running a mazda RX-7 FPR, its good to 150 psi, fully adjustable, and chrome too, definitly made a difference, ~$120 new, I think I'm set at 42psi, up from 35? I'll have to check when I get home. Makes the car run a little rich at low rpm, but perfect for 10-11psi boost, Soon to come is the RX7 fuel pump:cool:

#9 Dennis ex24

Dennis ex24

    Subaru Disaster

  • Members
  • 2,683 posts
  • Phila, Pa

Posted 11 November 2003 - 02:20 PM

ive been sourcing some units for mustangs that are for sale on ebay for pretty cheap.

this is something im definatley going to need to do like soon foir the XT, ill post updates when i get around to doing it.

#10 whiplash-smile

whiplash-smile

    USMB Regular

  • Members
  • PipPipPip
  • 35 posts
  • Colorado

Posted 11 November 2003 - 07:58 PM

Do It Sidewayz that is a great idea! I have access to several of those FPR's.. so amodifying I go! Hey what do you mean by the "Top"?

#11 whiplash-smile

whiplash-smile

    USMB Regular

  • Members
  • PipPipPip
  • 35 posts
  • Colorado

Posted 11 November 2003 - 08:05 PM

Free Range, what year RX-7 did you get yours from?

#12 whiplash-smile

whiplash-smile

    USMB Regular

  • Members
  • PipPipPip
  • 35 posts
  • Colorado

Posted 11 November 2003 - 08:07 PM

Caleb, man I just read my response to your initial post and....(hanging my head) sorry man! I didn't mean to disregard your input! And thanks for giving it.

Sam

#13 subarubrat

subarubrat

    Duty Honor Country

  • Members
  • 1,185 posts
  • Bealeton, VA

Posted 11 November 2003 - 09:13 PM

On my Impreza with aftermarket turbo I use larger injectors and a RRFPR (rising rate fuel pressure regulator) this increases the fuel pressure in relation to boost. It would be a good solution on it's own for the EA82T.

#14 electryc_monk

electryc_monk

    Air-ride Airehead

  • Members
  • 1,581 posts
  • Denton, Tx

Posted 11 November 2003 - 11:50 PM

so what is stopping us from adding to this thread a list of injectors and their flow rates?

you know something simple:
injector name/ engine from/ flow rate
FHI / EA81/ 450 GPS (or some other format?)

is that too much to ask for - for us visual thinkers?

#15 78TurboBrat

78TurboBrat

    USMB is life!

  • Members
  • 191 posts
  • Frisco Texas

Posted 12 November 2003 - 10:57 PM

ok welcome to the board, and im sorry but i couldnt resist,
for those who like to run higher boost, why not make an inlet with a nice big hole in it, and hook a tube to it, and just run a fuel pump wide open into the intake. i think you could run as much boost as you would want :banana: :banana:

Ok on the serious note now , yeah you can modify the FPR but it will only do so much for you if you dont have the head pressure from a good pump behind it. i am running a 81 Fiat Fuel pump, and i noticed a difference after changing the pump, and of course the FPR. Using the stock injectors. seems somewhere i read that the Lexus v-6 from a 97 model , injectors are suppose to be like 750 or something. cant rememeber numbers, but i used a set of them in a 89 Toy Supra running 19 psi of boost. fast car, but kept eating bearings and cranks. so we dropped the boost fixed the car and sold it to get rid of it. got rid of that head ache.

#16 whiplash-smile

whiplash-smile

    USMB Regular

  • Members
  • PipPipPip
  • 35 posts
  • Colorado

Posted 12 November 2003 - 11:24 PM

78Turbobrat, this would kind of fall under the same tone of response I gave to Caleb earlier... The stock Suburu pump will flow more fuel and build more pressure than what it is currently doing. At the level (boost wise) I am at, I don't need an exotic or p.i.t.a. setup, the stock stuff will work fine, if I convince it to do the extra work. My initial post was for someone who actually had already done this, so I could be lazy and use HIS(or hers) wheel. I wasn't debating the feasibilty of this modification, as I KNOW it can be done. I do appreciate what you and everyoneelse has to say. I will be hooking up a FPR and fuel pressure guage with an air/fuel ratio meter in the next week and I will let everyone know the results of the small changes you can make to our stock parts and the results that are obtained.

Sam

#17 calebz

calebz

    Andys Coupe killed my cat

  • Administrator
  • 7,547 posts
  • Tacoma

Posted 12 November 2003 - 11:51 PM

Right on! let us know how it comes out.. I'm interested in how much you can sqeeze out of a stock setup

#18 MaroonDuneDoom

MaroonDuneDoom

    Stick It To The Man!!!

  • Members
  • 604 posts
  • Casper,Wy

Posted 13 November 2003 - 12:12 AM

i'm interested in how the HELL you do this fuel pressure boosting pump mod or whatever. definitely let us know when your all done

best wishes

#19 78TurboBrat

78TurboBrat

    USMB is life!

  • Members
  • 191 posts
  • Frisco Texas

Posted 13 November 2003 - 12:23 AM

whiplash , it seems like you asked for advice on how to do something, and then gripe about how to do something we tell you how to do it. maybe i am the only one who sees it that way. but then again maybe i am seeing it all wrong, and not answering what you are after.

But yeah i am with calebez on this on, let me know how you plan on pushing more flow out of the stock pump, it can only pump so much till it peters out with enough flow. i only used the fiat pump cause i knoew it would work, and i had one new laying around.
besides the 78 turbo brat is a work of parts put together to make a fun ad fast car, but yet very respectable to the neighborhood ricers running around along with the mustangs who dont laugh at the car anymore.


but yeah let us know what you find out. and let us know how much more you can squeeze out of the stock parts.:banghead: :banghead:

#20 Do It Sidewayz

Do It Sidewayz

    Subaru Fanatic!

  • Members
  • 464 posts
  • Toronto, Ontario

Posted 13 November 2003 - 12:36 AM

the stock pump is rated to produce something like 70 PSI all the time. Meaning in stock configuation the pump sends back almost half the pressure to the tank.

You have MORE than enough fuel to run 45-50 PSI with the stock pump. Trust me. We've done it for liek 3 years.

#21 Free Range

Free Range

    Chicken or the egg, hmm?

  • Members
  • 215 posts
  • Missoula, MT

Posted 13 November 2003 - 12:05 PM

I'm going to sit on the fence with do it sideways, you can do his cheep mod, or go the spendy route with any aftermarket RRFPR(what I did), either way, until the fuel pump takes a dump on you(by all means put a bigger pump on there if you have it lying around) you should have plenty of fuel to stock injectors. oh I'm running ~44psi, turned it to 48 once and car was way rich, hard to start, but at boost was yet again more peppy... I'll leave it at 44, for now.

the RRFPR also helped with the 9psi boost fuel cut issue, now at ~12 psi boost the car won't usually cut out until WOT in 3rd pulling up a hill, when it used to do it at 5000RPM, BLOODY FUEL CUT, grrrr

I too would like to see what bigger injectors will fit on these motors.

On a side note, run some Lucas injector cleaner, and a new fuel filter just in case.

Injoy!

#22 whiplash-smile

whiplash-smile

    USMB Regular

  • Members
  • PipPipPip
  • 35 posts
  • Colorado

Posted 13 November 2003 - 10:02 PM

Originally posted by calebz
Right on! let us know how it comes out.. I'm interested in how much you can sqeeze out of a stock setup



I will post bio of the car and some pics of it and the mods I have made in the next couple of days as well as the future stuff for it.

#23 whiplash-smile

whiplash-smile

    USMB Regular

  • Members
  • PipPipPip
  • 35 posts
  • Colorado

Posted 13 November 2003 - 10:07 PM

Originally posted by MaroonDuneDoom
i'm interested in how the HELL you do this fuel pressure boosting pump mod or whatever. definitely let us know when your all done

best wishes



Thanks man! But for the record there is no "Boosting" of the fuel pump... it will be doing it's every day ho-hum job... we will just be taking better advantage of this work it has been doing... it looks like a number of this boards regulars are already aware of what i speak of and are taking advantage of it... some are not. I will do my best to give the correct information so any mods people make in the future will be somewhat educated guesses.

#24 Adam N.D.J.

Adam N.D.J.

    Quite Rusty, but working.

  • Members
  • 3,238 posts
  • Medford, Oregon

Posted 13 November 2003 - 10:17 PM

The stock fuel pump is good for about 80psi, (least the one in the Brat is, it's off an EA82T). So thats good there. As for putting in an adjustable FPR, that isn't a problem either. Just grab a JEGG's, J.C. Whitney, Summit or racing supply mag of your choice and look for an FI adjustable FPR, they can be had for as little as 10 buck. Then your take your shiney new FPR and plumb it into your existing lines on the RETURN hose. Remove the vacume line from the stock unit (which is built into the fuel rail anyways, not much you can do with it without any work), and plug in the new FPR. The other one will over ride the stock one. Since the restriction is downstream of the old FPR the new one will work the way you want it. I've done this for many years on many different rigs, this is how I'm pushing 12psi into an EA81T without any problems. And if you spend the cash and get a Rising Rate one, you won't have to worry about the rich idle syndrome that I've got right now. The stock injectors will handle 80psi without any problems, least on mine none of the hoses burst or anything. If your going to go much higher than that though, I would build a new fuel rail and use injectors that don't have the rubber hose connection. Also make sure you don't have one of those el' cheapo plastic fuel filters (like from autozone), get a good quality all metal one (I got mine from napa). I had a plastic one, and at 45psi the entire end of it burst, really really bad thing.

#25 whiplash-smile

whiplash-smile

    USMB Regular

  • Members
  • PipPipPip
  • 35 posts
  • Colorado

Posted 13 November 2003 - 11:08 PM

Originally posted by 78TurboBrat
whiplash , it seems like you asked for advice on how to do something, and then gripe about how to do something we tell you how to do it. maybe i am the only one who sees it that way. but then again maybe i am seeing it all wrong, and not answering what you are after.

I know that it seems like I am dismissing your input, I am not, however. I have looked at and evaluated your responses to my question, and responded a little bluntly, but hopefully you have an idea what I am trying to accomplish now.

But yeah i am with calebez on this on, let me know how you plan on pushing more flow out of the stock pump, it can only pump so much till it peters out with enough flow. i only used the fiat pump cause i knoew it would work, and i had one new laying around.
besides the 78 turbo brat is a work of parts put together to make a fun ad fast car, but yet very respectable to the neighborhood ricers running around along with the mustangs who dont laugh at the car anymore.

Actually I am not trying to get anymore flow out of the stock pump, just utilize a little more of its potential. Likewisw the the stock injectors will stay in place and I will use some of their untapped potential as well. I think it is great that you managed to make your vehicle work with parts from different manufacturers, more power to you.

but yeah let us know what you find out. and let us know how much more you can squeeze out of the stock parts.:banghead: :banghead:



I will let you know what works and what doesn't, and if I hit my head on any walls.

Sam




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users