hahn stage 2 fuel pressure and turnin up the boost

[lilbayz311]

Q#1:i got my kit and its all installed its pretty quik. my only problem is i cant get the fuel pressure to run higher than 90 psi at high rpms. i am buying a boost controller to turn up the boost to 10 at least until i rebuild my engine and 90 psi fuel pressure is only good for the boost its runnin now. the kit included a high flow fuel pump, higher flow injectors, and a fuel pressure regulator. with all those extra fuel mods you would think i could drown the mofo if i wanted with fuel but i turn the valve more open and it still stays the same 90psi. i tried turning up the idle to 60psi but at high rpms, it was the same 90. would this mean i have a leak somwhere or what?

Q#2:i am just wondering what all i have to do to turn up the boost on my hahn kit besides get a boost controller and up the fuel? am i able to just install a boost controller and turn up the boost a couple notches and have everything work with it in this kit? all i would be turning it up to at most is 10psi

any help from people who have actually had experience with this kit and know what they are talking about would be appreciated

 

[BigRand]

Personally, I wouldn't turn your boost up till summer time, I don't know how cold it gets in utah (not very much I assume) but with an internal gate and cold weather that spells boost spike in certin situations, hence I would turn it up not past 8psi on that turbo unless you are ready to pull apart the motor and do a rebuild in a week or two.


As for the fuel pressure issues, I would first, scrap the accel intank fuel pump, and just go for the walbro 255 (your gonna need it when you turn up the boost later as well), also the Cartech fmu that is provided from hahn we all know is pretty much crap, see if you can't find a 12:1 vortec in the classifieds, I bet that is your problem right there. (p.s. turn your idle fuel pressure back to stock)


Now wait a sec as I'm writing this I just realized something big here, how are you adjusting your idle fuel presssure using an fmu. It shouldn't do anything unless boost is present.

It should be
boost pressure = fuel pressure
0psi = 43.5psi
1psi = 55.5psi
2psi = 67.5psi
3psi = 79.5psi
4psi = 91.5psi
5psi = 103.5psi
6psi = 115.5psi
7psi = 127.5psi
8psi = 139.5psi
9psi = 151.5psi
10psi = 163.5psi

Now I'm pretty sure the stock injectors and upgraded fuel pump dont' really go past 8psi (possibly 9, depending on airflow from turbo) on this setup.

If you do want to run more fuel, your gonna have to upgrade the injectors, get rid of the fmu setup and go with an SFMU that you CAN adjust idle fuel presssure with, so you can go with smaller size injectors ie 270cc or 310cc. Or you can go with bigger injectors and a 1:1 fuel pressure regulator, and go with injectors that will take you upwards of 20psi starting around 440cc


Either way get the walbro fuel pump in, and be prepared to scrap the cartech fmu once you decide to raise the boost pressure. P.S. 10psi on a stock block untuned usually spells "boom"

 

[lilbayz311]

its crazy different people opinions on different things. ive heard i could turn up my boost pretty much safely to 12 psi on a stock block at least for racing then run constantly on 10 psi besides that if i had adequate fuel. the main reason i wanna turn up my boost a little is ### i have only seen tops about 6psi and the stage 2 is supposed to be runnin on 8psi. i can adjust me fuel pressure regulator idle by turning an allan screw in or out and top end by openning or closing this valve on the regulator. but oh well i guess

 

[FORMONTOYA]

It should be
boost pressure = fuel pressure
0psi = 43.5psi
1psi = 55.5psi
2psi = 67.5psi
3psi = 79.5psi
4psi = 91.5psi
5psi = 103.5psi
6psi = 115.5psi
7psi = 127.5psi
8psi = 139.5psi
9psi = 151.5psi
10psi = 163.5psi

Of course I'm a 4G63 guy, however, I believe this to be wrong...............

Your base pressure = XX.
Once you apply boost a true 1:1 FPR should add 1PSI of fuel pressure to every 1PSI of boost.....ie:
1PSI boost = XX + 1PSI FP
2PSI boost = XX + 2PSI FP and so on........

For me running 43.5PSI base FP it would equal 53.5PSI fuel pressure running 10PSI of boost (43.5BFP + 10PSI boost = 53.5RFP). I can imagine that it's any different for you guys.

I just can't imagine running 163.5PSI fuel pressure..........I would hate to see what the equation would be if I tried to run 20PSI, what's that work out to............250+PSI fuel pressure...........things would start to fly apart.


Please correct me if I'm wrong.

 

[VelocitàPaola]

Please correct me if I'm wrong.

Nope, you're right on the money! I made a graph once of the approximate fuel pressures with an FMU under boost, but I suppose it got lost after that server transfer.

 

[cs82685]

Of course I'm a 4G63 guy, however, I believe this to be wrong...............

Your base pressure = XX.
Once you apply boost a true 1:1 FPR should add 1PSI of fuel pressure to every 1PSI of boost.....ie:
1PSI boost = XX + 1PSI FP
2PSI boost = XX + 2PSI FP and so on........

For me running 43.5PSI base FP it would equal 53.5PSI fuel pressure running 10PSI of boost (43.5BFP + 10PSI boost = 53.5RFP). I can imagine that it's any different for you guys.

I just can't imagine running 163.5PSI fuel pressure..........I would hate to see what the equation would be if I tried to run 20PSI, what's that work out to............250+PSI fuel pressure...........things would start to fly apart.


Please correct me if I'm wrong.

You're right about the 1:1 however, the fpr's we use are 12:1, so 1psi adds 12psi.... you know the deal you're a wiseman, , this is what we need for our puny stock injectors. Usually the 420a's aren't using 1:1 fprs unless if their on an 8-injector setup such as the portfueler, or MSnS.

To the OP, I noticed, my stock injectors would not flow anymore than about 110psi. Yeah, you may need more fuel, but if the injectors are at 100% duty cycle before this, it's not gonna happen, you're just not gonna get the desired amount of fuel needed without upgrading injectors. You might want to do as said above, swap out the fuel pump to start, supposedly the new cartech is better than the older one, but eventually, you'll probably swap it out for something better.

As for idle fuel pressure, I believe hahn says 47-55psi which would put your static above and beyond that (probably around 60-70psi) Not to disagree with bigrand b/c I know he know's his stuff, but this is what I have learned and remember from researching

lilbayz, don't run 12psi, if you wanna go ahead and get a boost controller so after the pressure drop you see 8psi, go ahead, but don't push past that if your not ready to rebuild.

Paul, Randy correct me if I'm wrong, I don't want to be giving him any wrong info.

Now to the wisemen and mods, is the maximum fuel pressure going to change with injectors. I feel like it wouldn't, so if he can only see 90psi and a walbro doesn't help, wouldn't he then need to upgrade injectors so that his fp's needed are not over that 90psi. Or, would using larger fuel lines just allow more fuel to pass at the same psi?

 

[FORMONTOYA]

First off I want to clarify that I don't know "squat" about the 420A, hence the stupid question above. It just seems weird to me that someone would build a kit that puts 163.5PSI to an injector, it just seems like it would blow apart, IDK.

It would seem a better idea to increase the injector size in stead of increasing fuel pressure (that much) to achieve the desired fuel flow.

This really shows the difference between how one goes about turbo-ing their car.

 

[VelocitàPaola]

First off I want to clarify that I don't know "squat" about the 420A, hence the stupid question above. It just seems weird to me that someone would build a kit that puts 163.5PSI to an injector, it just seems like it would blow apart, IDK.

It would seem a better idea to increase the injector size in stead of increasing fuel pressure (that much) to achieve the desired fuel flow.

This really shows the difference between how one goes about turbo-ing their car.

Corey, you're right about the 12:1 thing. I didn't even catch that in Jim's first post... so, good job.

Jim, the reason we increase fuel pressure so much, is two-fold. For one, it's easy and cheap. No other method allows us to "control" our fuel flow under boost like an FMU. Second, the stock FPR and ECU can't really handle larger injectors. The AFR would be sky high with anything larger than the stockers... and to compensate, we have to replace the stock FPR with an S-FMU and/or an S-AFC just to get the car to idle correctly.

 

[VelocitàPaola]

Now to the wisemen and mods, is the maximum fuel pressure going to change with injectors. I feel like it wouldn't, so if he can only see 90psi and a walbro doesn't help, wouldn't he then need to upgrade injectors so that his fp's needed are not over that 90psi. Or, would using larger fuel lines just allow more fuel to pass at the same psi?

Fuel lines don't really need to be upgraded unless the total flow rate of the injectors becomes larger than the flow rate of the fuel lines. It can happen, but you'll probably need more than 800cc/min injectors when it does. You have to think of it in terms of "bottlenecks;" "which component in my fuel system can flow the least?" In most correctly operating systems, that bottleneck is the fuel injectors. That's a good thing. Adding larger lines to a fuel system that doesn't need them won't help at all, because the injectors are still going to flow the same amount based on fuel pressure and the PWM they're receiving from the ECU.

Like you said, the maximum fuel pressure doesn't really change between injectors... in fact, you ideally want to keep it as low as possible. Why? Well, you're sort of choosing between mechanical (S-FMU, FMU, etc.) and electronic (MS, 034EIC, Portfueler, etc.) means to control your fuel flow. With large injectors and some sort of electronic method, you have complete control over your fuel because whatever electronic system you're using can adjust fuel flow by adjusting the electronic pulses going to the injector.

Whereas, if you were using an FMU/S-FMU to control fuel and the stock ECU, even with larger injectors, you'll need to increase fuel pressure to effectively add more fuel. Because of your ML/FCD, your stock ECU is still sending pulses thinking it's at 0inHg vacuum; thus, the FMU/S-FMU is solely responsible for adding the needed fuel under boost.

With that explanation, I hope you can now understand why you don't really need an FMU/S-FMU with MS (that wasn't directed at anyone, but I've heard the question come up before). In fact, the only reason you need a 1:1 AFPR is because fuel injectors have a maximum duty cycle (amount of time open vs. amount of time closed per unit of time), which is usually around 80%. In order to not hit this maximum duty cycle in an attempt to provide adequate amounts of fuel throughout the whole vac/boost range, you need to vary the fuel pressure a little.

Beyond that, you don't need any adjustment in fuel pressure at all; and those astronomical fuel pressures FMUs create are simply not needed with a stand-alone system. FMUs add fuel in a rather sloppy and imprecise manner, too. They basically add fuel according to a linear algorithm, whereas the changes required to maintain a stoichiometric AFR are not. However, the fact remains that it's cheap and easy, so it is also ideal for the beginner not going past 8psi of boost.

 

[lilbayz311]

just fyi, the kit did include 26 lbs/hr fuel injectors im not sure exactly how much bigger those are than the stock ones. but so you guys are saying i can turn up the boost just to 8 psi entering the engine to be safe? ok im cool with that for the winter til i rebuild my engine and get some $ again. will i need to add any more fuel for the increase to 8 psi? if so, what would be the most efficient way? or would an s-afc be ideal even right now?

 

[DSMcrazy3]

SAFC will never be ideal, honestly. Stock injectors are 190cc which equals about 18lb/hr. 26lb/hr = 270cc.

A common set-up people run is 30lb injectors and an SFMU.

I currently have stock injectors, walbro 255 and 12:1 FMU and I lean out under boost in 3rd, 4th and 5th gears. So whether or not that set-up will work is based on the current condition of your stock injectors.

 

[BigRand]

just to clarify about my thread, and the fuel pressure numbers I posted, I was posting them hypothetically, but as it was stated earlier our stock injectors can't barely flow over 110psi, thus making the rest of the numbers useless, but I posted them none the less to get my point across.

Now I'm sorry if I posted this incorrectly about what our stock fuel presssure is but I was under the impression it was 43.5psi (however I forget if that is static or idle so I would like this one answered).

I would also like to know from the original poster is how he had adjusted his stock fuel pressure using the current setup from hahn>? because I dont' think you can, so I"m looking for clarification or a current modlist.

 

[DSMcrazy3]

Stock - 47-50 psi

Static - 60 psi

 

[FORMONTOYA]

I must say that after reading this post (and a couple of others) I have a new respect for the 420A guys. Ya'll have quite a few more "hoops" to jump through than I imagined in order to get the turbo functioning properly.

 

[totaleclipse_05]

So theoretically, we should only boost to 6 psi max on 12:1 FMU, Walbro 255lph HP, and stock injectors? That 255lph HP maxes out at 120 psi I read. Why has everyone always said that 8 psi on that setup is the max and not 6?

 

[lilbayz311]

k i got a question.. my setup hits 6psi boost in first gear tops, about 7psi goin from 2nd to 3rd, and now that i adjust the actuater arm 1 turn shorter, about 8 psi in 3rd gear. so now im confused man. i want 8 psi at least in 1st and 2nd gears ### that when its the most beneficial. but if i get it to be 8 psi in 1st, its only logical that it would be pushin 9-10psi in 3rd? so should i keep it where it is, or adjust to be at 8psi in first gear?

 

[lilbayz311]

and to bigrand.. ill try my best to show you how hahn manages it. first i had to take out the stock fuel pressure regulater, flip the fitting upside down and cap the old outlet like so:

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next we ran a braided steel fuel line from the out side of the fuel rail that is originally capped off, to the new fuel pressure regulator

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after that we had to run a new fuel return line back to the fuel pump from the engine compartment. the allen scew adjusts the idle, the little valve adjust the static. i hope this answers or makes you better understand what i was talking about when i say i adjust the pressure. i know the pics are small

 

[lilbayz311]

and since ive heard so much negativity about the safc used on our cars and how it doesnt work as well as on other cars, could somebody please point me in the right direction for precise fuel management in the future that is affordable? wouldnt the safc get the job done tho?

 

[BigRand]

Makes sense to me about the hahn fuel setup.

I think the boost "problems" you are experiencing have to do with the internal wastegate opening early, boost pressure isn't exactly accurate. Someone else feel free to elaborate on that if they feel that is the problem.

Try your test again, but in 2nd gear don't floor it, just ease into it and go to about 90-95% of full throttle, and see if the results are the same.

I don't know too much about internal gates since I've been using external ones only.

 

[DSMcrazy3]

My car boosts higher in 2nd and 3rd than first. But since first goes by so quickly, I really don't care.

 

[lilbayz311]

ya i understand that. all im asking is should i have it boost 6psi in 1st gear or 8psi? i guess ill just call tech support and ask them

 

[totaleclipse_05]

Leave it so it only boosts to 6 psi in first gear. Like you said, it boosts higher in 2nd and 3rd gear than first. If you adjust the wastegate for 8 psi for first gear, you will get higher boost levels in 2nd and 3rd and that won't be good.

Like Josh said, 1st goes by fast enough anyways that the extra 2 psi won't be noticed by much.