IceY2K1

iTrader: (3)

Boost--OEM--------FMU------
PSI---- FPR--4:1---6:1---8:1
0--------43----43----43----43
1--------44----44----44----44
2--------45----45----45----45
3--------46----46----46----46
4--------47----47----47----49
5--------48----48----48----57
6--------49----49----53----65
7--------50----50----59----73
8--------51----51----65----81
9--------52----53----71----89
10-------53----57----77----97

Now, correct me if I'm wrong PLEASE. I used the FMU equation 1/2(static fuel pressure at idle) + (Boost PSI x FMU ratio). BOLD pressures are where the FMU ratio "kicks in" and increases the fuel pressure above what the OEM FPR does.

Assumptions: static fuel pressure at idle of 34psi and the OEM FPR will increase pressure at a 1:1 ratio until the FMU surpasses it.

Here's some MAX bhp calcs for 80% and 100% Duty Cycle with 370s using a recommended BSFC=0.60:
www.doubleshotsindustries.com/max/370s.PDF

Here's some MAX bhp calcs for 80% and 100% Duty Cycle with 550s using a recommended BSFC=0.60:
www.doubleshotsindustries.com/max/550s.PDF

Stephen Max

iTrader: (59)

That is how I understand it.

slimer

iTrader: (13)

that helps.

steve

and isn't it hook 'em horns?

IceY2K1

iTrader: (3)

I'm not done yet...focking server won't let me attach.

IceY2K1

iTrader: (3)

MAX bhp calcs for 370s using a recommended BSFC=0.60:

http://us.f1f.yahoofs.com/bc/36b49ea...rJjPABkdlkm7xb

IceY2K1

iTrader: (3)

If anybody wants any other cc/min injector, I can do it no sweat.

Bags

iTrader: (3)

555's and the stock 4th gens


BTW When I click the links, I get an error message

IceY2K1

iTrader: (3)

Okay, it's yahoo then.

I'll have to have somebody host it then, since the .orgy attach feature isn't working...at least on PDFs.

JeffesonM

iTrader: (5)

icy... email me at jmerchan@hcsus.jnj.com if you want me to host some stuff

IceY2K1

iTrader: (3)

JeffesonM - YGM!

Thanks.

Bags

iTrader: (3)

Keep bags533@aol.com on file, I'll host ANYTHING from you

IceY2K1

iTrader: (3)

Sent them to both of you. Hopefully, one of you can get them up for me.

Thanks!

IceY2K1

iTrader: (3)

Alright...quit hogging them and post them up guys.

BigDogJonx

iTrader: (7)

Alright as stupid as this sounds, Im totally lost on how the 4:1 6:1 and 8:1 chart you have works. I understand the 1:1 since its raises 1psi per pound of boost. But the others, im lost. I dont get how you got the FP's at certain PSI. This whole FMU calculation has been boggling me from day one and im sure others.

Lets say I plan on running 5lbs of boost with a 4:1 disc. Well according to the calc 1/2(34)+5x4=37. So I only need 37psi of Fuel Pressure? That dont make sense. And then also dont understand the whole concept of when it kicks in. I thought standard vortech fmu kicks in when it see's boost?

Dont ask me how I dont know this, i just never could grasp it. I always went by what Ive heard in that if Im doing about 10psi boost i want to be around 80-90psi FP if Im on stock injectors.

Dixit

Stephen Max

iTrader: (59)

I'm going to avoid the question of what you need at 5 psi of boost. But what fuel pressure you get at 5 psi is going to depend on which fuel pressure regulating device produces the higher pressure. With a 4:1 disk, the fmu will only produce 37 psi at 5 psi of boost, like you say, but the oem fpr will produce 48 psi (43 + 5). Therefore the fpr will determine what your fuel pressure is. What this says is that it is pointless to have a 4:1 disk if your only boosting to 5 psi. The fmu will never enter into play. Like Icey's table shows, you need at least an 8:1 disk before you get any effect from the fmu. In low boost cases, it is sufficient to tune with an SAFC based on the fuel pressure the fpr provides at a 1:1 rate.

JeffesonM

iTrader: (5)

Okay, they're up.

370cc map

550cc map

IceY2K1

iTrader: (3)

Thanks........

I need to do the same for stock injectors...what are they? I've read 240, 250, 260 for you 4th geners...

Stephen Max

iTrader: (59)

When looking at those charts to determine what fuel pressure you need to obtain a particular power level, keep in mind:

The boost pressure in the intake manifold acts against the fuel pressure in the injector. So if you have 5 psi boost pressure, and your 1:1 fpr is giving you 48 psi of fuel pressure, the fuel delivery rate should be based on an actual pressure of 48 - 5 = 43 psi. Don't make the mistake of thinking you have 48 psi fuel pressure and therefore according to the chart your 370 cc/min injectors are good for 297 hp at 80% duty cycle.

Stephen Max

iTrader: (59)

Well, I measured 270 cc/min at 43 psi with my homemade injector flow tester. But when I tested one of my 370 cc/min injectors, I got 386 cc/min. So I'm totally perplexed. Interestingly, 270 X 370/386 = 259 cc/min.

So take your pick: 240, 259, 270 cc/min.

IceY2K1

iTrader: (3)

SOOOoooo back when Mardi called 'duh' or was it 'durrr', he was mistaken.

If that's true, my .xls should hold the cc/min and bhp constant from 43psi up for the FPR chart.

I have a feeling this is where the "1/2(static)" part of the FMU equation comes from.

IceY2K1

iTrader: (3)

Stephen,

It's not that I don't believe you, just not sure about this.

Is there anyway you can use one of your stock injectors and fuel test setup to verify this?

Basically, what I'm thinking is to take a sealed jar with a lid, mount a valve stem and the injector to the lid. Then pressurize the jar using the valve stem with 5psi and perform your measurement test with 48psig. Then release the pressure and perform the measurement again, but with 43psig. If they are the same, you're correct.

If it's not worth your time, that's fine, I'll talk with RC Engineering to see what they say.

Stephen Max

iTrader: (59)

I basically restated what I read in one of Corky Bell's books. I probably should have given a reference.

But here's another thought experiment for you. Take an empty balloon and inflate it with a straw at whatever psi you can generate. Let's say 10 psi. So the straw is the injector, the balloon is the intake plenum and your lungs are the fuel pump. Now try to inflate a balloon that is already pressurized to 15 psi, and again all you can generate is 10 psi. I think you'll find the balloon will inflate you rather than the other way around. The same has to hold true with fuel injectors, that is, it is the pressure differential that determines flow, not just the pressure in the fuel line.

That is also why the oem fuel injection system is designed with a 1:1 fpr - so that at idle, when manifold vacuum is at about -9 psig, the fuel pressure is 34 psi, and at WOT (unboosted) the fuel pressure is 43 psi. The fpr ensures that the pressure differential remains constant so that fuel delivery is dependent only on injector pulse width and not on fuel pressure variations.

Stephen Max

iTrader: (59)

P.S. It don't hurt my feelins' none if you don't believe me. I'm here to learn as well as help out, so if I need the BS flag raised on me, don't hesitate. Differences of opinion are welcome.

IceY2K1

iTrader: (3)

That's what I meant...*I* just don't "see" how that works, but your example is helping. Except that the injector is only open for a limited time, not constant, so it acts more like a check valve and *MIGHT* not be a 1:1 ratio. I'd definitely accept a % of reverse pressure, but not 100%. Kind of like how increasing the pressure to the injector is not a 1:1 ratio on output flow. This would explain some of that loss in flow, but not 1:1. I guess that's why you're the mechanical engineer though and I'm not.

Still pondering how, why, etc.....I'll get it eventually.

ilumo

Thanks stephen,
So this essentially means, at every boost level, you have to subtract the pressure from boost from the pressure of the injector.
So for example, using his 'chart', at 12 PSI of boost, using the 6:1 ratio disk, the PSIG would be 89 psi. But then it would have to fight against 12 PSI in the intake plnum coming in, so the effective pressure would be 89 -12 psi = 77 psi. and that equates to around 377 BHP.

Now, will the pressure at the fuel injector still be the 89 PSI, or will it see 77 psi. Probably the latter? hmmmm..

ilumo

I think I see how that works too... When NA, the pressure will remain constant, but the DC% will just go up if needed.

Ramius83

F*ck, that means my 370cc's are already maxed out.......shiat......

ilumo

unless you wanna try triple digit pressure on the INJECTORS... but then ... could the Fuel pump handle that?

Stephen Max

iTrader: (59)

I don't think so. If you graph the fuel delivery capacity vs fuel pressure for Walbro pumps you get the graph below. I've added a line that represents power producing capacity versus gallons of fuel delivered, assuming .6 brake specific fuel consumption (lb/hr-hp). So with the Walbro 255 lph high pressure pump, at 100 psi it is limited to about 27 gallons an hour. (27 gallons/hr X 7 lb/gal)/.6 lb/hr-hp = 315 hp. That is a surprisingly low number. If you are actually burning fuel at a rate corresponding to .5, the power goes up to 375 hp. The actual numbers people are getting vs fuel pressure may vary quite a bit depending on how they are tuned, but the general trend is correct: fuel delivery suffers a very severe drop off once you get above ~90 psi.

slimer

iTrader: (13)

What is the difference with adding the in-line fuel pump to those measurements?

Stephen Max

iTrader: (59)

Good question. I don't have any data for the Vortech aux pump.

slimer

iTrader: (13)

i was just asking to see if delivery efficiency would be higher if you added more fuel with the aux pump.

Bags

iTrader: (3)

Icy here you go..another resource.. I just post the direct pics

IceY2K1

iTrader: (3)

The inline pumps can only supply what the in-tank pump can feed it.

The reason the fuel pressure takes a nose dive after 80psi typically on most aftermarket in-tank pumps(90psi on HP models) is that the bypass safety valve begins to open. Your stock pumps opens far sooner. This bypass valve is not present in the inline pumps, since it would change fuel volume.

The secret to getting consistent fuel volume even at higher pressures is to have a constant or for more fuel volume is to increase in supply voltage/amps to the pump. As you add more electrical accessories or lose voltage as the alternator ages, your fuel pump loses output capacity.

I have some RC Engineering data found running pumps at 13.5 vs. 16.5 volts and where the bypass valve begins to open in my latest Turbo&High-Tech Performance magazine. Basically, after 80psi of fuel pressure, you're at risk even with a Walbro 255lph HP. 90+psi is very bad. Guys here who run 90+psi with the Walbro *THINK* just because they have the pressure, they have enough fuel. However, as RC Engineering showed, just because you have enough pressure, that doesn't mean you have the VOLUME of fuel required to keep the LEAN demons away.

Bags

iTrader: (3)

I am so lost, it's not funny.

I think I learn and I don't. I may need to buy a book.

I was with dixit on the FMU pressure thing. Stephen's example of the balloon made perfect sense to me.

I need to do more reading. The minute I think I am making forward progress, I trip into a thread like this and think once again, I don't know jack.

Keep it coming fellas. I will keep reading and re-reading and searching the internet for foolow up articles.


And I am not embarassed to say it, this made my head hurt. Excuse me while I go put on my helmet.

IceY2K1

iTrader: (3)

I have them for the inline MSD, some OEMs, Walbro GSS341, etc. at different input voltages.

I've been trying to figure out a way to summarize the data withOUT typing it all in. Hopefully, by tomorrow I can figure something out.

slimer

iTrader: (13)

bags--thats why i cant wait till i visit my sister in Austin next month.

I can actually sit down with Stephen and pick his brain in person.

Stephen Max

iTrader: (59)

That's not going to hurt, is it?

slimer

iTrader: (13)

not too much

IceY2K1

iTrader: (3)

Stephen,

So, what would be a better assumption?

The fuel pressure rises from 43psi-to-XXpsi, but the bhp stays constant at whatever 43psi supported?

If so, that would mean my "fmu kick-in" point would be lower to whenever the ratio, 1/2(SFP)+(psi*fmu), exceeds 43psi, correct?

I DO NOT want to mislead anybody, so please help me fix my chart to be more accurate.

Thanks.