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Old 11-29-2001, 01:35 AM   #1
Midwayman
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Exclamation Fuel correction for high output NA(long)

I have been doing quite a bit of research on high output NA ej engines.

Specifically the ej25 putting out about and in excess of 200hp (That magical number... )

Thing is if you've been following the thread you know that the stock fuel system isnt upto the challenge of 200hp without going static. My car is exhibiting signs that its hitting the static limit. It acceration smoothly, stutters then as rpms climb it smooths out again ( fitting in line with the idea that the fuel system is okay, suddenly goes static resulting in a very rich condition, then leans out as the rpms climb again)

So what is the best way to fix this?

Start with the basics... 43psi stock fuel pressure with 280cc injectors. This gives us enough fuel for maybe the low-mid 190's before going static.

Running the BSFC calcs I found that 55psi fuel pressure will supply 200hp with a bit of room to spare (infact 50psi would probably do it)

Ive heard rumors that the ECU can compensate for upto about 25% more fuel pressure. Can anyone comfirm? This would be good for the closed loop mode at least. Open loop mode would be okay, but probably a bit rich.

First lets address with issue of raise fuel pressure on a NA car. Does anyone know if rrfpr's would work? I know the stock fuel pressure is referenced to the manifold pressure, but it seems that even the mildest ramp rate on the RRFPR would create a run rich condition. So what is the solution to raise fuel pressure in a NA car?

Ive read up on the Weapon R FPR.... reports are the gauge is inaccurate, and that they leak (apparently based on 6 units JC sports received a year or more ago.... only reference I could find)
$165 or so...

The Paxton FPR.... one mention on the boards, found the paxton site, but no mention of the fpr, the price or what it does. Saw a pic and it looks like the weapon R, gauge attached.

ISR carries a FPR for $199, functionality unknown.

Vortech make the s-fmu (that right?) for $300 (on site) that is a rrfpr with changeable plates. They have a fpr with only one plate that is considerably cheaper that still appears to be a rrfpr?

Cartech has several good rrfpr's for about $200. They also make a static FPR that appears to be more like what a NA car would need for $150ish. No real info on it though.

Seems a direct replacement for the stock FPR is what is needed. Any leads on the right equipment, or what works? (turbo guys??? you know fpr's!)

Can the ecu compensate the the extra fuel in closed loop, and what is the highest safe pressure to run the stock injectors? Ive heard stories about injectors sticking open above a certain pressure.

So Say we have the fuel pressure worked out. We need to tune the high end. S-AFC or hyper field fuel controlers seems to be the tickets. SAFC Ive found for $300 shipped. (groupbuycenter) and the hyper field... I know is cheaper, but with less adjustment.

Both of these should work fine in open loop.... exactly where they are needed.

Other questions. What fuel pressure is the stock fuel pump good to? Upgraded fuel pumps have a reputation for increasing idle fuel pressure to 50psi or so (up from 36ish) will a replacement FPR fix this?

Hopefully someone knowledgeable with exceeding the stock fuel system limits in a NA car can help out. Oh, and yes Ive searched extensively.
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Old 11-29-2001, 10:35 AM   #2
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Anyone? I'm looking for suggestions as well! Thanks!
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Old 11-29-2001, 10:40 AM   #3
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As you've seen from my last post here.. I am also very interested in the answers.

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Old 11-29-2001, 10:50 AM   #4
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Me four!

Midwayman - that's some good initial research
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Old 11-29-2001, 01:16 PM   #5
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Not a whole lot to contribute, but I'll at least add something..

A FPR should do the trick, rumour has it that they were running lean on a 2000 with a header back brullen system.. then Shiv was misquoted as saying the stock injectors can only hold 170hp..

I would think that if you maxed out everything.. cam, heads, headers, exhaust, intake.. etc.. you may need some more fuel pressure..

It wouldn't be much, and the guys at COBB tuning may be able to give a yay or nay, but I would think a RRFPR or just an FPR would do it.

Korey
..oh and a bit of a bump too..
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Old 11-29-2001, 02:13 PM   #6
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Probably came from the fact that the formula for injectors calculates 170hp.

Inj. Size(lbs/hr) X Duty Cycle / BSFC = HP per injector.

280cc / 10.5 = 26.6 lbs/hr

26.6(lbs/hr) X .80(80%dutycycle) / .50 (b.s.f.c) = 42.6(hp per injector)

42.6 X 4(number of inj) = 170.6hp



Ow. I think I hurt myself.
Of course I'm just repeating information I've found. I personally don't know what I'm talking about.
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Old 11-29-2001, 02:16 PM   #7
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Do you have a means of checking you're A/F ratio? Sometimes a stutter or buck could be the car running VERY lean. I'm not sure of your setup, so I don't know.

Yes, you could raise fuel pressure, however, the car won't properly compensate at idle, and the car will run rich. RRFPR's can raise pressure as revs increase (vacuum decreases) and Cartech does make such a thing, so idle will not be affected.
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Old 11-29-2001, 02:28 PM   #8
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Well I am not really sure what you have done to your car in the way of mods. Simply in any case with more fuel you need more air so that you can make a bigger bang. You need to keep the air and fuel mixture realitively stoich for the most pure power.

So in any case if you getting more air into the engine then you want to run more fuel. Depending on how much air is flowing into the engine you should be able to figure out how much fuel you are going to need to make a nice stoich reading at WOT. Just get a S-AFC and you can use that to set your Air/Fuel Ratio and it has volt indicator you can use as a guage to set it correctly.

Finally if you want more HP NA, then get NA cams to draw in more air. There a million other things you can do to draw in more air, of course a new filter will work quite well, as well as ram air. Anything that makes it easier for the engine to draw more air in will allow you to add more fuel. As for running a high flow fuel pump, you can easily do it with a good aftermarket FPR. That is what I am doing on a Turbo setup and it works well.


Calculations:
You can set the duty cycle higher but that is not recommended. Since then the injectors are basicly stuck open.

Inj. Size(lbs/hr) X Duty Cycle / BSFC = HP per injector.

280cc / 10.5 = 26.6 lbs/hr

26.6(lbs/hr) X .95(95%dutycycle) / .50 (b.s.f.c) = 50.54(hp per injector)

50.54X 4(number of inj) = 202.16hp

But there are other key factors that can change the output, these things are Fuel Pressure and BSFC (Better the fuel the lower the number)

One good cheap mod to do is the Parallel Fuel Line Conversion that way all your injectors get a more equal amount of fuel, where as stock they do not.

Last edited by skywalker; 11-29-2001 at 02:52 PM.
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Old 11-29-2001, 03:49 PM   #9
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Brian - Get your hands on a Walbro fuel pump. It'll raise your pressure all around and you shouldn't have that much trouble then. If you want, I have a source to get S-AFC's for around $200 used.

FYI, I believe Brian has intake, exhaust, and NA cams.
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Old 11-29-2001, 04:05 PM   #10
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Does the stuttering happen in the 3500 - 4000 rpm range? Might be the dreaded over sensitive knock sensor..
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Old 11-29-2001, 04:28 PM   #11
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RRFPR increase fuel preasure as manifold preasure increases. I would think that these only work properly with forced induction. Infact, they may not increase fp until they see postive manifold preasure which you will never have with an NA engine.
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Old 11-29-2001, 04:45 PM   #12
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Like 8 said... I have intake, catback, and cams. I am very likely pushing the static limit. Cams along bring it upto 179 hp. Plus intake and catback I more than likely into the 190's somewhere. If I had headers (let alone heads) I expect to be clearly over the static limit.

FWIW the 170 hp limit is very very conservative. Im making calcs with .475 BSFC (smack inthe middle) and 85% duty.

8- I know the the fuel pump will raise the pressure, trouble is it raises the idle pressure too much.

I know a FPR would be good, better than a RRFPR, but which one? Im especially interested in experiences with the paxton unit.

Id love a A/F gauge, but at this point unless I go whole-hog its not worth it. I have a my00 so I cant use the front o2 sensor and the rear is worthless. A gauge plus a normal o2 sensor runs near $200.

As for more air easier than more fuel.... yah I know that. Tough bit is I think Im getting to the limit of what I can do and be in good tune. (I know others have done more, but I want to do it right and not rely on static injectors for extra fuel)
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Old 11-29-2001, 05:07 PM   #13
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Allwheeldrift,

RFPR increase pressure with and increase in pressure, this is correct. But remember your manifold pressure is below atmospheric at idle (vacuum), and it INCREASES as power increases (ie, the throttle plate opens, and pressure increases to higher absolute pressures.... ie lower vacuum). So RFPR do work for NA engines, you just have to source them correctly (I've used one on a 600 cc na cycle engine).

Also, I've read several papers that state that maximum power is obtain at slightly rich (or lean) conditions, not stoichiometric. Can't remember if it's rich or lean, though (most people will say lean.... that's what I'd guess, too).

--Roy
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Old 11-29-2001, 05:10 PM   #14
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Midwayman - you and I are on the same brain wave! It's like I'm asking the questions and starting this thread.. but it's not me... hrmm..(btw thanks for the info in the thread I DID start.. )

I feel the exact same. I want to get the NA cams.. but I want to do it right and not just 'get by'. (Use a bandaid here and a piece of gum and viola!) I am eagerly awaiting answers to your questions and if you can get this straightened out.. I will probably be following in your footsteps..

I might just have to break down and contact Cobb for answers on this since I will be going through them for the cams and install. Only problem is, I feel guilty calling the with questions. Especially, since I haven't commited to buying the cams yet... just another newbie calling and probably asking the same questions everyone else is... hehe.

"I pity the foo!"



p.s. Don't mean to derail this thread.. but what's the difference between FPR and RRFPR? FPR is a constant pressure increase while an RRFPR increases pressure in relation to a change in vacuum pressure?

Last edited by RigdenZW; 11-29-2001 at 05:21 PM.
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Old 11-29-2001, 05:17 PM   #15
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Let me say that the car isnt running badly. I just feel that its not running at its full potential, and especially in the light of me planning on doing more, I want to know where I go next.

Please dont take this as a indication that you *need* to do all this to run the street cams. By all means get them. You'll love em. Just asking, what next?
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Old 11-29-2001, 05:25 PM   #16
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I know.. it's just that right now all I have is the ganz CAI and a slightly bigger than stock midpipe and muffler. When I get the cams I will eventually look into headers and a better cat back system. Maybe even go with a new CAI like cobbs.

Like you said.. that's borderline limit for a 280cc injector system.. if not over.

Just planning for the future right the first time.

Anyways.. enough of my situation.. back to Midwayman's questions!

<-- shuts up.
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Old 11-29-2001, 06:25 PM   #17
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... as I'm running on stock fuel system, I only did few aggressive runs after Brullen header installed, no CE problem so far & the car runs good. My setup including Brullen header/catback, street cams, PRM intake, UOR Pulley.
Parallel Fuel Line sounds good, I'm also considering Larry's chip.
Midwayman, Brullen header is sweet, don't miss it!
Benjamin
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Old 11-29-2001, 11:28 PM   #18
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Default Godamn! Midwayman's a mind reader,,

Count me in also,,,,My mods are Cobb intake,U/O pulley,Magnecors,Random Tech cat and Stromung catback,,my cams arrived yest. from Cobb(Tues. install I hope).Headers are next come Spring.
Lets keep this alive ,seems like alot of interest.
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Old 11-30-2001, 12:08 AM   #19
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Brian, you need to install some guages so we can find out what is going on in there!

You also know my notes on this as well. Ever since the weather got colder, I've been running lean at over 5000 rpm at WOT. Even with using 35% enrichment using an SAFC its still running lean. I'm actualy afraid to run any more correction for fear that I may lock up the injectors. I've also had to enrich the entire rev band from 5 to 20% just to stay out of the lean side of the a/f meter.

The only plus side is the extra gob of power from idle to 5000 rpm. Then the power drops off.
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Old 11-30-2001, 03:01 AM   #20
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Shiv was not misquoted

http://www.i-club.com/forums/showthr...+specific+fuel

[quote]...Using the same math, stock 280cc injectors would support approx 170 horsepower...[/qoute]

[edit - fixed URL to work]

Last edited by ImprezaRS dot com; 12-01-2001 at 02:22 PM.
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Old 11-30-2001, 03:53 AM   #21
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Default Walbro Fuel Pump

Quote:
Originally posted by 8Complex
Brian - Get your hands on a Walbro fuel pump. It'll raise your pressure all around and you shouldn't have that much trouble then. If you want, I have a source to get S-AFC's for around $200 used.

FYI, I believe Brian has intake, exhaust, and NA cams.
Hey 8Complex,

Where can I get a Walbro fuel pump from? I am looking for one for my XT6 which is running into a really really LEAN condition between 5k-6k rpm. I was thinking about getting a FPR but why when I can just get an upgrade fuel pump and kill 2 birds with one stone? I already have an A-SAFC installed. Thanks!
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Old 11-30-2001, 06:13 AM   #22
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2 birds, 1 stone.

Brian - Get the same one that comes in the Ludespeed stage III kit, I ran fine at idle with it, though it was slightly high, the ECU compensated for it pretty well and I didn't have any stalling problems of anything.

Kevin Thomas - Are you running the stock pump now without any mods on the car? That sounds just like a weak pump. Honestly if you're planning on going FI with that XT6, I would consider a fuel pump that would be an upgrade for a TT Supra or RX-7 turbo. The pump you have would be about the pump you'd upgrade to with one of the Walbro's that most of us RS-T's are using, so you'd need to go even bigger to get even more out of it. Truely, you should consider larger injectors if you're running out of fuel... not sure there are hacks for the XT-6 quite as easy to come by as the hacks for the RS-T's.
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Old 11-30-2001, 08:10 AM   #23
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Good post Brian. I have much the same problem. It's not so much a shudder or anything violent, it feels more like there is a bubble of air not getting through the system. My other thoughts besides fuel pressure were 1)high flow cat, 2)I need to have my valve lash set. I know my roommates Integra had a similar problem before he got his JUN headers and the problem was solved. I'm still leaning towards the fuel issue also though.

Tim Albert
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Old 11-30-2001, 08:28 AM   #24
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Default Re: Walbro Fuel Pump

Quote:
Originally posted by Kevin Thomas
Where can I get a Walbro fuel pump from? I am looking for one for my XT6 which is running into a really really LEAN condition between 5k-6k rpm. I was thinking about getting a FPR but why when I can just get an upgrade fuel pump and kill 2 birds with one stone? I already have an A-SAFC installed. Thanks!

Try here. Walbro Mustang 255 Hi-pressure pump GSS340 $105.00.

http://www.jdsperformance.com/index....=245&fcmd=item



Charlie
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Old 11-30-2001, 09:22 AM   #25
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[quote]Originally posted by ImprezaRS dot com
Shiv was not misquoted

http://www.i-club.com/forums/showth...e+specific+fuel

Quote:
...Using the same math, stock 280cc injectors would support approx 170 horsepower...[/qoute]
Quote:
Originally posted by shiv
Larry-- those statements represent a rule of thumb when it comes to proper injector sizing. I never said that the stock injectors couldn't support more than 165-170hp. I simply said that they were sized (by the powertrain engineers) for those hp levels. A few months ago, I wrote a story in SCC describing how these rules of thumbs can "disproven" by nothing more than reducing BSFC and increasing max. desired duty cycle. Both variables are multipliers so small tweaks impact calculated hp levels dramatically. This was described quite comprehensively in a number of my SCC project stories (Miata, 2.5RS and RX-7).

Now quite misquoting me

Shiv
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