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Discussion Starter · #1 ·
Do you still have to use a boost dependent fuel regulator on the SDS? I had it in my mind that the digital systems would fix what some call the "band-aid" Bell rising rate regs that I have to run on my stock turbo car. I saw that you were installing a Bosch reg; or was that just a normal type of regualtor? This would make the digital FI systems less attractive to me if I still have to run the Bell. Thanks guy.
 

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Discussion Starter · #2 ·
The stock FPR is fixed at 35-36psi and I dont know that Haltech or any of the other systems can eliminate the need or compensate for an adjustable/rising rate FPR. Maybe 240z turbo or someone else can answer that.

Scottie
 

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Discussion Starter · #3 ·
RE: How about it Tech II, Haltech users???

What fuel pressure regulators are you using? Also, Scottie how have you got that fuel rail mounted? It looks good and clean on your car. Is it an affordable piece?
 

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RE: How about it Tech II, Haltech users (long)

I'm using a TEC-II, and I have a bosch 45psi standard regulator, and 50lb/hr injectors. BTW, the standard regulator's job is not to keep the fuel rail at a constant pressure. It is supposed to keep the difference between the fuel rail pressure and the manifold pressure at a constant value. This is done so that a given injector pulsewidth always delivers the same amount of fuel, regardless of the manifold pressure.

The only reason that you would have to use the rising rate regulator would be if you had injectors that were too small for the amount of power that you desire, and for whatever reason, you did not want to change the injectors. In this case, the rising rate regulator is used to make the injector 'look bigger', by raising the fuel pressure when you are on boost.

One nice thing about the rising rate regulator is that it allows better injector pulsewidth resolution near idle, which should help off-boost driveability. Also, it's what you need to use if you plan to keep the stock FI system.

One bad thing about the rising rate FPR (from annecdotal accounts only - I haven't used one) is that the pressure regulation is less repeatable when in the rising rate mode, which can lead to inconsistent performance. This is probably a big part of the bad reputation this thing has gotten.

Another thing is that the rising rate regulator generally has a fairly steep rising rate curve - say, from 36psi at zero boost to 100psi at 10psi boost, or on that order. It's like that because fuel flow increases with the square root of fuel pressure, so to double the fuel flow, you have to quadruple the pressure.

Because of this, you need to be _really_ careful with your selection of fuel pumps. The stock turbo pump is internally pressure relieved at 65psi, as I recall, so it would be less than ideal for a rising rate FPR application.
All pumps tend to have decreasing flow capacity as the pressure goes up, so you need to be absolutely sure that your pump can flow the amount of fuel that you require at the pressure you require. I suspect that this might be another aspect of the rising rate FPR's bad rep - poor fuel pump selection.

As an example, let's say that you want to get 300hp out of your stock 19lb/hr injectors. For simplicity, let's assume that you don't mind going all the way to 100% duty cycle (i.e., you have no headroom - 300 hp is all you will ever get), and that your FI system can do 100% duty cycle.

The injectors at the stock 36psi can deliver 114lbs/hr, which is enough for roughly 228hp (again, at 100% duty cycle). To get 300hp, you will need to flow about 150lb/hr, which is an increase of 150/114 = 1.316, or about 32%. Since the fuel flow varies with the square root of pressure, you will have to increase the pressure across the injector by (1.316**2), or about 73%.

This equates to roughly 62psi across the injector. I'm also going to guess that you needed about 12psi of manifold pressure to get to that horsepower level, so the pump will have to able to supply at least 150lb/hr of fuel at a pressure of 62+12=74psi.

Okay... probably more info than you were looking for, but this question comes up alot. Hope it helps...
 

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RE: Thanks TimZ

That's about what I was going to say, but man I didn't want to write it all out!! I also don't like to trick injectors by running excessive fuel pressure. Anything above about 65 PSI can cause the injectors to have fits and not perform correctly. Hard for them to recover correctly when dealing with 100PSI. Rising rates are a must when dealing with stock systems that can't compensate for boost correctly, but when you go to a programmable sytem you need to ditch the rising rate and get the right injectors.
grerg
71 240z
 

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Discussion Starter · #6 ·
RE: Thanks TimZ

I have the Bosch FPR installed and set at 38 psi (w/o vacuum) at idle. The info I have on the Bosch is that it has a steady rising rate of 1 psi of fuel pressure for each psi of boost. So I expect to see 50 psi on the pressure gauge at 12 psi of boost. I should have the halfshaft in tonight. However, I do not have a fuel pressure gauge installed so I need to figure out how to read the EFI pressure gauge tool that is connected inline under the hood, while I am driving. Will have to try and tape the gauge to the windshield or something. Since the Bosch is supposed to let the stock injectors flow +20%, I will have to remap the fuel in the SDS as if the sock injectors actually have a flow rate of 310cc.

I will post my results as soon as I have them.
 

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Discussion Starter · #7 ·
RE: TimZ that was not 2 much info THANKS!

Just right for now. Gives me plenty to digest and plan for when I raise the bar for my car. I got a file of stuff like this gem I print out and revisit when I need it.
 

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Discussion Starter · #8 ·
RE: Anyone attempting the Talon inj yet?

The one's Scottie mentioned. I would like to find some that cost less than 100 each. I can't see spending 600 on MY car for these things. I'm sure others have asked about the 300 ZXT or TT injectors working, but will they fit and flow more?
 

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Scottie...please read....

Scottie wrote:
-------------------------------
I have the Bosch FPR installed and set at 38 psi (w/o vacuum) at idle. The info I have on the Bosch is that it has a steady rising rate of 1 psi of fuel pressure for each psi of boost. So I expect to see 50 psi on the pressure gauge at 12 psi of boost. I should have the halfshaft in tonight. However, I do not have a fuel pressure gauge installed so I need to figure out how to read the EFI pressure gauge tool that is connected inline under the hood, while I am driving. Will have to try and tape the gauge to the windshield or something. Since the Bosch is supposed to let the stock injectors flow +20%, I will have to remap the fuel in the SDS as if the sock injectors actually have a flow rate of 310cc.

Scottie...
Maybe I misread this, but the Bosch regulator as you described it is _not_ a rising rate FPR. It is maintaining a constant 38psi pressure differential across the injector. Because of this, it will not cause your injectors to have _any_ additional flow capacity, it will only allow them to maintain their rated flow while you are on boost. If you remap to compensate for higher flowing injectors, you will actually be mapping yourself 20% lean. Be careful - this could get costly...
 
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