?s On Raising the Fuel Pressure...

[johnnyballs180]

First: Me babbling. Farther down: My real questions.

First...I've just started reading up on and learning about upgrading fuel systems and providing adequate fuel to a motor.

There's a lot of info out there, and I've spent a couple days trying to sift through all the irrelevant stuff. Finally, I've decided to just go ahead and ask...

Are there any negative side-effects to consider/expect if one were to raise the factory fuel pressure (with an adjustable FPR)?

From what I've read (Not SR20 specific), causing (or increasing) leaks, wearing down of or a failing fuel pump, and the injector's inability to open against the high fuel pressure were some pretty common problems.

In my case, I have the factory 370cc injectors on my SR20DEt, Sard 265 lp/h fuel pump, Nismo adj. FPR, factory ECU, new narrow-band o2, and I replaced all the rubber fuel lines. I need more fuel, and I will upgrade the injectors, wide-band o2, ecu, and then a tune (...oh jesus...) a while from now... but in the meantime, if the negatives don't out-weigh the pros, I'd like to increase the fuel pressure.

There's a few cool online calculators that give an estimate of what the end-result of raising the fuel pressure would be, and other sites that describe what size injectors a given motor needs for a certain HP and BSFC.

Farther down...1) Is BSFC (Brake Specific Fuel Consuption) specific to every car (case-by-case), or is it generic between the same type of car?

2) With an un-programable ECU, will raising the fuel pressure cause the computer to attempt to compensate [anything]?

3) Is the duty cycle pre-determined by the computer based off of the TPS? And what is the max duty cycle?

4) And, y'know, what other bad stuff and all that...

I've read 60psi max, 70psi max, no more than 15% increase max, etc. I haven't read anything negative on anything set below 60psi.

I know there's a lot going on in this post, but I think this is all really interesting, and I would HATE to do something wrong when fuel comes into question.

Im not wearing my flame retardant pants today, so please don't flame me.

[del82]

Christ...ok, well lets try to answer a few of these...

Firstly, and foremost, if you've done nothing and/or your engine is getting enough fuel, and particularly maintains stoichometric AFR while cruising, you don't want to fiddle with it. Adding more fuel only equates to more power if you have a fuel map problemb: you can get more air in too

That said, moving on to some questions.1. BSFC: never heard of this term. either its a nerd-level technical aspect of performance tuning, that's beyond me, or someone's BSing you.

2. Yes, the computer will compensate with shorter duty cycles, eventually. OBDI is kind of stupid about this, though, and tends to just run off its tables instead of the actual numbers coming in from the engine. Turning up the fuel pressure in this case just tends to result in bad gas mileage. This is also why so many OBDI cars (particularly Ford engines, actually) start idling/cruising like **** after a few performance mods.

3. Actually, the ECU stores a fuel table for a baseline in OBDII, and then uses the TPS, MAF, and O2 sensor (while cruising) to make adjustments as necessary. Changing any of these sensors (except the TPS) tends to require reflashing the PROM to change the fuel tables around to compensate.

4. As for your concerns on raising the pressure...to be honest, flow is the more important factor. Make sure you can feed your engine properly, then get your fuel pressure where you want it. So long as the flow is good, you can make minor adjustments to fuel pressure to get better atomization, and make very fine-tune adjustments to the fuel curve under WOT, which can help with flat spots in the curve, but you usually need a dyno to set all that up properly anyway, and most dyno shops can assist you with all this stuff

Forewarning though: fuel maps aren't really my specialty. Sure, it's important and all, but whats above pretty much exhausts my knowledge of the subject, heh. I'd always been more concerned with flow rates over pressure. I suppose there's some science to it though, the Honda guys are all about it, and god knows they need every extra HP they can get

[usmctankmech]

So let me get this str8..... your running a upgraded fuel pump, and stock injectors on a SR20, and your running 60 psi fuel Pressure? Crazy Talk! lolWhat cams are you running and how much boost?

[johnnyballs180]

lolSome of the smarter guys I've talked to moved over from the Honda scene.... hahaha. I get tossed around by this one Civic here.. and I'm okay with that, because he's just, flat-out, a good driver. Not to mention his car keeps up with mine in a straight.

My biggest problem (other than money?) is the lack of readily-available resources. I'd LOVE to spend a day or two on a dyno, but for right now, I have to hold off.

http://autospeed.com/cms/A_110216/article.html..kind of answered one of my own questions.

As far as the computer reverting to tables, I thought that until WOT, the computer goes off of its' sensors?

http://www.deatschwerks.com/ca...s.phph ... c.htmlThat a couple of the websites I was talking about.

I think it's nearly impossible to know exactly how much fuel I'm needing unless I have a wideband. What I do know, is that suddenly I've introduced a lot more air into the motor, and it can't be happy about that. I did a few mods without a real clear understanding of proper fueling. Air+fuel=power. More air with the same amount of fuel=...lean.

Regardless of what I should have done or should do, I'd still like to know exactly how a car would react to an increase in fuel pressure. Apparently, a lot of people use it to add just a pinch of richness.

Since I can't feed my engine "properly" just yet, higher pressure would be an interem thing.

usmctankmech, no I'm not running 60psi fuel. I was saying that I've read that 60psi is what most people recommend max psi, though I did see a few tests between some factory Nissan injectors and a few Bosch injectors, taken up to 80psi... they recorded no problems whatsoever.And stock cams.

I know what I want to do with the motor, but I also know how much money I make.:P

[usmctankmech]

ok well i just kno you can get better resultsif you lean it out a lil. I mean i got HKS 264 cams , FMIC, 15 Psi boost, 300zx fuel filter, stock injectors and mine likes it better at like 42-50psi, but that may be just cuz im cammed idk.

[johnnyballs180]

why would you get better resuilts if you lean it out? are you using your original turbo, or did you upgrade? there's no way in hell leaning-out is going to do anything good for me; gt28 from a t25, 370cc injectors are already maxed out.

[del82]

Lean air = hotter burn = more power. You can see this from anyone that uses an acetylene torch, they turn up the oxygen, not the fuel, to power up the torch

The only reason not to do this in the automotive world is, well, the heat part. Running lean tends to cook valves and rings very quickly, or even soften the pistons enough that the next combustion cycle could blow a hole in the crown of it. Fun stuff. Next time you watch top fuel drag racing (if you do), look closely as the cars near the end of the track, at the exhaust pipes. Those little sparks coming out are pieces of molten piston and rings and such. Top fuel is currently held up by metallurgy, rather than any actual engine technology. Oh, and then by the limit of Gs that can be sustained by the human body Hows that for going off-topic?

[johnnyballs180]

hahahah

i've always though it was cool that they could still go faster. i understand what you're saying about increasing the air.. but in my car, THAT'S the problem i'm faced with. the whole point is to get more fuel, not air, because i already have more air than the car's ever seen before....and so far, i've probably lucked out more than anything.

if usmctankmech is right, then wonderful, but i don't understand how going lean in this application is anything near good..?

[usmctankmech]

Im running the stock T25 on the 13 red top. Im running 264 cams, an fmic, etc. My fuel pressure is set in the 45-50 psi range. And at 15 pounds of boost it likes it snappy. but those r just my results.

[johnnyballs180]

you're running 15 psi on your stock turbo..? and what do cams have to do with fuel requirements? if you've turned the boost up that much, i imagine a little more fuel would help, but i don't see what 264 cams have to do with anything.and what does "snappy" mean,

mine likes it better at like 42-50psi

...what. what likes what better, why, and how do you know? i'm sorry, but i've become really lost.

[del82]

Oh, the Honda guys are good to talk to about fuel maps and such because they have to slave over them and every other dinky thing to squeeze every last bit of power from their anemic grocery-getter econobox engines.

Then there's the theatrics when they're driving around corners, their race cars lift a tire off the ground like a dog taking a leak, and for the same reason: both of em can't do it right without lifting a leg.

I may be a bit biased.

Off topic again, heh heh...but anyway, again lean means more power, at the expense of the engine's survivability. You can get away with a little bit, but you do have to be careful when leaning out the fuel map.

[johnnyballs180]

which is kind of the point i was getting at... i feel dangerous pushing one ata of boost (dropped it down to about .75). i think the turbo will last, but i'm worried about the pistons and cylinders.

i guess the best solution is a total engine management system and bigger (based off of those sites i posted previously, i'm looking at 740cc injectors. if i don't need them now, i [hopefully] soon will).. and then of course, a tune.

thanks for your input though, dude.

[usmctankmech]

Snappy as in Crisper Throttle Response thats just what i run with my setup . The cams dont realy apply but it was just an example.