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Discussion Starter · #1 ·
I have been trying for a couple of days to test the Bosch FPR with the stock injectors to see how the fuel pressure reacts with increasing boost. I was running 95% duty cycle and the primary goal of the test was to raise the fuel pressure to see if the duty cycle would go down, allowing me to raise the boost.

We have had a drought here in Central Florida with some forest fires starting up again. Now our prayers for rain have been answered, but just as I am trying to test the FPR. Drought, test the Z, drought, test the Z, hmmmmm. Anyways, its raining again, but like the man in "Dirty Harry" said "...I gots to know". I dont have a fuel pressure gauge installed but I did borrow a Snap-on Fuel Injection pressure gauge which I taped to the windshield. Crude but effective. In between showers but on wet roads, any hint of boost produced ugly wheelpsin but I did manage to boldly push it to 5psi and..........it works as advertised, albeit a very limited test. I had the FPR adjusted to 38psi at idle with no vacuum and saw 43-44psi on the gauge at 5psi or thereabouts, trying to keep the car and me in one piece. There was no fluctuation or flickering so I suspect that the fuel pressure would continue to increase at the rate of 1psi per each psi of boost.

TIM, I apologize if I kept referring to this FPR as a rising rate FPR, but I think you can understand why.

Since it appears to be working as advertised, I can only assume that the claim of increasing an injector's flow rate by 20% is also correct since I do not have a way to prove that. Next test is to remap the SDS as if the injectors flow rate is 310cc instead of 260cc, run it up to 8.5psi boost and check the duty cycle. If it did come down, that screeching sound you hear is 245 tires fighting for grip.

More details as I find out.

Scottie
 

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You can increase the flow of the injectors by raising your base fuel pressure. If the Bosch is adjustable you turn up the pressure to increase the flow. Set base pressure with the vacuum line off the regulator so you get a nice steady reading. Pressure should be like 45PSI with the car running and the vacuum line off. You keep bumping up the base fuel pressure to increase the flow out of the injectors. as long as your pump can handle it and you don't try to push it too much this works great. it's practically the only way to tune a car with a stock fuel injection system. Running too lean on the tope end? Bump the pressure up a few pounds at a time. Too rich? Go the other way. On programmable systems the pressure is only upped when you run out of injector, like you are doing Scottie. Try to keep the pressure under 70 psi at full boost (about 50PSI base) for best injector performance. You should not need a rising rate regulator for any car with a programmable system. Rising rates are the type that can be set to give 2, 3,4, etc extra pounds of fuel pressure for every pound of boost. keep the bosch if it is adjustable, Scottie. If not get an adjustable one. Down and dirty way is to take your stock regulator and squeeze it in a vise to make it 1/16 of an inch shorter. 0ld tech way to do it, but it works. I'd spend the money to get an adjustable one, bosch or otherwise.
greg
71 240z
 

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Discussion Starter · #3 ·
Thanks, Greg. Great advice for everyone. The Bosch is adjustable and I set it to 38psi anticipating 50psi with 12psi of boost. I anticipate I will be at max duty cycle by then, but the way the car is running now, I will be tickled at 12psi. Then I will try the DSM injectors.

The pump is a Bosch off a Porsche and I checked and that is the same FPR that the Porsche uses. Now if I could figure how to get those brakes.....
 

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By DSM are you referring to Diamond Star Motors injectors? Can you tell me the OD or do you know if they'll fit into the stock bosses?
 

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Scottie wrote:
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<snip> There was no fluctuation or flickering so I suspect that the fuel pressure would continue to increase at the rate of 1psi per each psi of boost.

Since it appears to be working as advertised, I can only assume that the claim of increasing an injector's flow rate by 20% is also correct since I do not have a way to prove that. Next test is to remap the SDS as if the injectors flow rate is 310cc instead of 260cc, run it up to 8.5psi boost and check the duty cycle. If it did come down, that screeching sound you hear is 245 tires fighting for grip.

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Scottie...
I just checked my service manual, and the stock pressure regulator was set at 36.3psi with zero manifold vacuum. From this, my calculations show that you should see a flow increase of about 2%. It doesn't matter that you go to higher rail pressures when you are on boost. The pressure across the injector is always 38psi. If anyone told you that this regulator, set to 38psi, would increase your fuel flow by 20%, they are just plain wrong.

Greg's post was correct. If your regulator is adjustable, the only way you are going to get increased flow is by increasing the base fuel pressure.

In order to get an increase of 20%, you will have to be running about 52psi at zero vacuum. Then, of course, you will need to be sure that the pump will flow enough for you at 64psi (the rail pressure) when you are making 12psi boost. Fun, isn't it?
 

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Discussion Starter · #6 ·
Bernard wrote:
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By DSM are you referring to Diamond Star Motors injectors? Can you tell me the OD or do you know if they'll fit into the stock bosses?


Bernard, the DSM injector is on the 90-94 Eclipse/Talon/Laser turbo and is physically the same as the Bosch. Both o-rings fit and it fits in the stock boss. Only difference is that the DSM inlet is not barbed and the inlet o.d. is slightly wider, but you might be able to get the hose over it. I have one but have not tried it yet..

TIM, you are right, this is fun. If the duty cycle did not come down with the FPR at 38psi, then I will start turning it up. What is a safe upper limit for the stock injectors? If it is set to 50psi at idle then I should theorethically see 62psi at 12psi of boost.

Scottie
 

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Scottie wrote:

TIM, you are right, this is fun. If the duty cycle did not come down with the FPR at 38psi, then I will start turning it up. What is a safe upper limit for the stock injectors? If it is set to 50psi at idle then I should theorethically see 62psi at 12psi of boost.

I don't have any experience in running the stock injectors at higher pressures, but I doubt that 62psi would present a problem - really, it's still just 50psi to the injector. The Bell rising rate FPR goes considerably higher than that, and apparently the injectors are holding up.

The fuel hoses will see the full 62psi, though.

I'd be more concerned about the capabilities of the fuel pump. What are you running?
 
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