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Old 08-26-2007, 06:08 PM   #1
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Default setting the 0~ fuel pressure

I cant figure out how to do it. Can someone help me?
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Old 08-26-2007, 07:42 PM   #2
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Dude, go to the Begi website and read the instructions.
Basically, you just remove the boost line and then turn the adjustment post... the one on top of the regulator (it uses an allen wrench and is secured in place by a small nut).
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Old 08-26-2007, 10:29 PM   #3
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I followed these instruction posted by Braineack with no problem.

"First off you want to make sure you adjust the top adjustment screw. So turn on the car and watch the gauge at idle. It should be at 35psi. Remove the vacuum line from the FMU (kink the line so there is no leak) and watch the fuel pressure increase. It should jump up. Turn the screw to tune. you'll want it somewhere inbetween 50-60psi. Closer to 60psi if no o2 clamp is being used on your system."

In this post- https://www.miataturbo.net/showthrea...ight=begi+afpr


Fuel pressure at 6 psi is right around 75psi. Is that good?
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Old 08-26-2007, 10:31 PM   #4
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stock injectors?

if so there's a formula for that.


(pressure ratio ^2 x 35psi) + boost....

so

6 + 14.7 / 14.7 = 1.408PR = 1.982PR2

(1.982 x 35) + 6 = 75psi of fuel....sounds like you are golden.
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Old 08-26-2007, 10:32 PM   #5
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Quote:
Originally Posted by Braineack View Post
stock injectors?

if so there's a formula for that.


(pressure ratio ^2 x 35psi) + boost....

so

6 + 14.7 / 14.7 = 1.408PR = 1.982PR2

(1.982 x 35) + 6 = 75psi of fuel....sounds like you are golden.


1.8L injectors.

Now tell me, with the 1.8l injectors stock fuel pump and the begi afpr, what should be the max pressure available. The adjustment screw in the AFPR is all the way in.

and

Do I need a 190 LPH HP pump with bigger injectors to run more boost?
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Old 08-26-2007, 11:51 PM   #6
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The max pressure available is not a function of the AFPR... it's of the fuel pump. The AFPR just regulates the starting fuel pressure at ~0 and then controls the rate of rise of fuel pressure above that at a PsiFuel:PsiBoost ratio. For example, the when the adjustment screw on the Begi is all the way in, you might be getting a 15:1 rate of rise. You get 15psi of extra fuel pressure on top of the ~0 amount for every psi of boost. If you back the screw all the way out, you might be down to just 2:1 or 3:1... at least I think that's how it works. (somebody back me up on this)

It's generally accepted that the stock fuel pump maxes out at 80psi. If you've got the adjustment screw all the way in the Begi will try to give you 15:1 until it reaches the max pressure the pump will handle and then it just won't be able to rise anymore. Fuel pumps do lose a little bit of their muscle with age... it's a good idea to test it... just completely clamp off the return line and the pressure will rise to max. It probably won't idle all that well, but shouldn't stall.

Brain's math says that you need 75psi of fuel at 6psi boost on stock injectors. You're running 1.8's, so you've got a little bit more fueling room... but I like a large margin of safety when it comes to mechanical fuel control. A boost spike or something unexpected might put you dangerously lean.

I wouldn't run any more boost until you can fuel more with a acceptable margin of error for your personal taste. A set of 305/310/330cc injectors is only about $50, and/or a Walbro190 is less than $100. It's cheap insurance.

PS, somebody back me up on how the Begi works or correct me, please.
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Old 09-05-2007, 01:17 PM   #7
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I have noticed lately that at 6-7 psi my fuel pressure will not read anymore than 70psi, Im affraid that I may be running a little lean at full boost. Do I need the 190 hp pump, bigger injectors or both?

Thanx
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Old 09-05-2007, 02:34 PM   #8
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i wouldn't boost anymore than 7psi with your injectors. but as of now you've reached the limits of your stock pump. tham same injectors at 100psi should prove to fuel around 190rwhp, where ever that may be.
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Old 09-05-2007, 02:46 PM   #9
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I have no plans on increasing boost until I get a wideband, but should I replace the pump just to be safe? Now when you say my injectors at 100psi should fuel around 190rwhp, woudnt I need to up the boost for that?

Is the general rule 10psi of fuel for 1 psi of boost?
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Old 09-05-2007, 03:17 PM   #10
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nope no general rule. strictly depends on the size of the injectors.
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Old 09-05-2007, 03:23 PM   #11
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Oh boy. I have never felt so confused. Being a newb sucks! As of now am I ok with 70 psi at 7psi on my 1.8 injectors? If i wanted to increase boost to say 10 psi what bandaids do I need?


Could you explain this to me in dummy terms?

stock injectors?

if so there's a formula for that.


(pressure ratio ^2 x 35psi) + boost....

so

6 + 14.7 / 14.7 = 1.408PR = 1.982PR2

(1.982 x 35) + 6 = 75psi of fuel....sounds like you are golden.
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Old 09-05-2007, 03:25 PM   #12
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It's all bullshit.

You want to tune the car? Get a wb and turn the adjusters on the FMU until the WB is happy. Nothing else matters.
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Old 09-05-2007, 03:48 PM   #13
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Quote:
Originally Posted by levnubhin View Post
Could you explain this to me in dummy terms?
If you have stock injectors then we can take into consideration that the car is perfectly fueled from the factory. So we can assume at a certain atmosphere if one set of fuleing works, then at higher atmosphere the same should apply.

The formula (pressure ratio^2 x base pressure) is the formula used for adding fuel to support boost with stock injectors.

think in stock fueling. (1PR x 35 ) = 35psi

For boost it requires the square of the pressure ratio.
6psi = (1.408PR)^2 = 1.982PR2

so likewise for stock fuel, we'd multiple the PR x the base pressure and get 70psi, we then add 1 psi of fuel per boost level for good measure, as the stock FPR is a 1:1 device so we mantain the rise.

When you add larger injectors, we cannt assume the fueling will be the same. so we have to estimate your BHP and then see what fuel pressure will best support the BHP level with the size of injectors you currently use.



or simply get a WB and turn the **** untill you have enough fuel.
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Old 09-05-2007, 04:20 PM   #14
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Quote:
Originally Posted by Braineack View Post

When you add larger injectors, we cannt assume the fueling will be the same. so we have to estimate your BHP and then see what fuel pressure will best support the BHP level with the size of injectors you currently use.



or simply get a WB and turn the **** untill you have enough fuel.

Ok, now I understand the formula for stock injectors. How do I fure out fuel for larger injectors?
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Old 09-05-2007, 04:38 PM   #15
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gotta estimate your horsepower...it's in my FAQ.

or simply use the calculator at Rc eng.
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