I'll be re-working and re-tuning my fuel system tomorrow.

I'll be using 400cc (38.1 LB) injectors and a Vortech S-FMU only and tuning for 15 psi.

I've read through all of Corbin's stuff and other sites on the web, but I want to get some more input from you guys.

Has anyone used these injectors? What are your static & idle fuel pressures? I need something to compare my numbers with to see if I'm close. I need a good starting point. The car is WAY out of tune now with my idle pressure at under 10 psi and using the 2.72" disc/dark spring combo in the S-FMU.

youll need about 14psi of idle pressure... at 15lbs of boost.. youll need about 95psi of fuel pressure at wot. use the 2nd largest disk/ring combo.

James

Here's what I had in mind.

The 235cc stock injectors supply ~252cc @ 50psi (stock fuel pressure)and ~276cc @ 60psi. HRC recommends 60psi static fuel pressure with the stock injectors... being turbo, I believe this slightly increased pressure is an acceptable number. Using these numbers, I can solve for the new calculated fuel pressure.

staticFP = ((Old / New)^2 * Rated)
staticFP = ((276 / 400)^2 * 43.5)
staticFP = 20.71 psi

My 400cc injectors will supply 276cc @ 20.71psi. So that's what I'll set my static fuel pressure to. Idle fuel pressure will take care of itself.

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My approximate Max HP, I'm guessing is 300. I'll need ~413.44cc per injector using a BSFC of 0.525 That's my approx. injector size @ 100% duty cycle (no S-AFC). Using Corbin's equation, I can solve for max fuel pressure.

maxFP = ((approx / actual)^2 * rated) + maxBoost
maxFP = ((413.44 / 400)^2 * 43.5) + 15
maxFP = 61.47 psi

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riseRatio = (maxFP - staticFP) / maxBoost
riseRatio = (61.47 - 20.71 ) / 15
riseRatio = 2.7173

The 2.47 disk with soft spring at 15psi should provide 67psi of fuel pressure. I can use the boost & bleed valves from there to get it perfect.



Am I on the right track here guys?

67 psi? at what boost level>?

use the hard, dark srping.. not the soft

15 psi manifold pressure

Use the long silver spring(it helps you to run a real low idle fuel pressure. 67 psi of fuel at 15 psi isnt going to be enough,even though the numbers might say so. As an example, my 310's, I run 20 psi at idle, with stock fuel trims, and at 13 psi boost, i'm well over 100 psi. Adding 90 cc's of fuel with the 400's wont be that much where you can run that little fuel pressure. Start off with long silver spring, at least the 2.72" disk/ring( I personally would use the largest disk, and open the bleed valve to tune down to the 2.72" disk rise rate, just so you know you have plenty of fuel availavle), and to run 15 psi, your fuel pressrue will prob be in the 90's somewhere. Run 15 psi at fully warmed up idle. Dont play with the static, it just makes it more complicated. Siueclipse is just about right on the money

actually dude.. its the dark harder spring that gives you the lower idle fuel pressure.

James

Ok... I'm currently using the dark spring and 2.72" disc... and I am able to get super low idle fuel pressures... so I'll leave that combo in.

Guys, I trust your word about the 95psi @ 15psi, but how the hell are you getting this number? Just telling me that I need ~95 max at 15 psi doesn't help me a whole lot when it comes to tuning becuase I need to know exactly what's going on here to make adjustments. Are you just guessing based on your experiences with other injectors, or are you calculating it? I need the theory man!

experience with injectors

at 16lbs of boost, i hit 90psi of fuel.. at 15, you will need aeound 95 with 400s. we are only telling you these numbers to get you started.. you have to fine tune from there

James

Okay... I've been studying up on rising rate fuel pressure regulators and tuning procedures & calculations. Corky Bell's web sites have helped clear up why my calculations are off. Here's what is suggested for fuel pressure tuning when turbocharging of an N/A engine-

"The fuel pressure required increases with the square of the boost pressure ratio".

Needed fuel pressure = ((Pressure Ratio ^ 2) x Base Fuel Pressure) + Boost

PR = 1 + bar
PR = 1 + 1.034
PR = 2.034

maxFP = (PR^2 * staticFP) + maxBoost

maxFP = (2.034^2 * 20.71) + 15
maxFP = 100.68


These calculations seem to make perfectly good sense to me and are close to what you guys have suggested to me as an INITIAL STARTING POINT. What do you think?

yep, thats more like it. I dont use the mathmatical formulas, I go by experience and playing around with fuel pressures, and tuning. What we have suggested is a great starting poing,and even if you are too rich, its always easy to tune it down, rather than flooring it wot adn be too lean..And about the spring, I tried using the short dark spring, and it would not let me go low enough..the adjustment screw was almost all the way out!:o Also, the short dark spring is supposed to have a slightly higher rate of gain in fuel pressure, according to Vortech directly..

i almost have your exact same setup. i have the vortech S-FMU and 415 cc/min injectors. i have the dark spring, the 2.72" disk, i run about 11-12 psi of fuel at idle, about 25 psi at static, and just below 100 psi of fuel around 15 psi of boost. i also have modified my vacuum restrictor. the hole in it is about twice the diameter than it was when it was unmodified.

why did you modify that restrictor ner?

I am surprised you guys can run that 2.72" disc with such big injectors. I have to use that one for my 310cc injectors. The 3" disc is just pig rich and the car studders at 7 psi of boost. The 2.72" disc fixed that, and the EGT's haven't climbed past 1550.

1996 Eclipse RS / 5-Speed / Body Components by Aerogear / Coated in Magnetic Red Metallic v2 - More at http://home.insightbb.com/~mgalyan/
Mark Galyan - Greenwood, Indiana

Nevermind, sorry. I forgot that I expected to be rich based on everyone else's numbers. I ran fatter fuel lines all the way from the fuel pump to a brand new high-flow fuel rail, and fat braided lines. I should need less fp than stock fuel guys with simply bigger injectors.


1996 Eclipse RS / 5-Speed / Body Components by Aerogear / Coated in Magnetic Red Metallic v2 - More at http://home.insightbb.com/~mgalyan/
Mark Galyan - Greenwood, Indiana