Injector Duration vs Fuel Pressure.

[HighMileage]

Hey gang,

Someone told me that increasing injector duration can be done instead of increasing fuel pressure.

From what I’ve always read here,1 pound of boost must be met with 1 pound of fuel press.

Is he right?

Thx.

 

[85tr]

Fuel pressure will be raised 1 to 1 by the fuel pressure regulator if not you will run lean and pop something.

 

[HighMileage]

Fuel pressure will be raised 1 to 1 by the fuel pressure regulator if not you will run lean and pop something.

I know,but he sez it can be done by increasing injector duration.

 

[85tr]

If you mean base fuel pressure then it may help but why not just turn fuel pressure up or get bigger injectors?

 

[ScottHeidinger]

Possible yes. Many N/A fuel injected cars don’t have adjustable FPR today probably to save on costs. They use no return line and regulate fuel pressure to a set PSI that doesn’t change. I think this is where your Turbo Tweak chip is also able to help save your engine from a certain death when fuel pumps crap out or can’t provide enough fuel the chip will provide more fuel in this manner to help keep it from leaning out but I’m not a chip programmer or tuner so I’m not sure. In my opinion I wouldn’t try to change the way our cars at set up with the adjustable FPR, if it was beneficial someone would have done it by now and we would all not have the adjustable FPR.


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[Nigel]

You would have to add a pressure correction to the injector pulse width, so for a given airflow you would now have different pulse width calculations based on pressure across the injector which could be all over the place. Having the regulator correct for pressure, now you only have to take into account airflow and injector flow calibrated to a base fuel pressure. You would also need a bigger injector to compensate for the boost then with the pressure regulated fuel system.

 

[HighMileage]

You would have to add a pressure correction to the injector pulse width, so for a given airflow you would now have different pulse width calculations based on pressure across the injector which could be all over the place. Having the regulator correct for pressure, now you only have to take into account airflow and injector flow calibrated to a base fuel pressure. You would also need a bigger injector to compensate for the boost then with the pressure regulated fuel system.

Hey Nigel.. Long time no hear from.

What’s going on here is some wisea** who has a turbo Saab sez he can easily just “chip his ECM and increase injector duration” if he wants to run more boost.

I told him he’s got to match FP to boost. He sez no. I’m thinking he’s full of sh*t,but want to ask here before I make an a** out of myself.

I’ve got to *represent* ya know...

 

[Nigel]

Hey Steve, just working on getting the car back together, no real new or change here. Hoping to be able to make it up to the valley come spring. I am guessing with a good fuel management system and programming you could compensate, but I think it may be easier with a fuel pressure regulator. I would not want to try on a factory ECM with a chip, not that I could burn a chip anyway.

 

[Jerryl]

It *can* work. Now . . . . . Captain obvious here . . .
If FP is constant at 45 psi and boost is 50, there is no fuel flow regardless of injector size or correction. It's the hard way of doing things on a car not designed to operate that way.

 

[Nigel]

It *can* work. Now . . . . . Captain obvious here . . .
If FP is constant at 45 psi and boost is 50, there is no fuel flow regardless of injector size or correction. It's the hard way of doing things on a car not designed to operate that way.

Good point.

 

[HighMileage]

Ok,so I’ll tell the guy that it can work,but it’s really not the correct way.

As for me,I’ve got an Accufab FP reg,a chip burned by Eric and his 60lb injectors and a DW301 pump and Alky. I was actually one of the first “guinnea pigs” to install the DW pump when it first came out. So,I’m good.


I’ve just never heard of increasing inj duration to substitute rising fuel pressure for increased boost.

 

[ScottHeidinger]

On the Saab they remap the ECU to increase boost. Some of the newer ones have software that will only allow more boost this way. They can’t just mess with the wastegate like we can so his story is a little twisted.


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[Jerryl]

It's pretty easy to test if you run an ECU with FP correction and loggimg. Tell him to test it and report back.

 

[HighMileage]

Hey Steve, just working on getting the car back together, no real new or change here. Hoping to be able to make it up to the valley come spring. I am guessing with a good fuel management system and programming you could compensate, but I think it may be easier with a fuel pressure regulator. I would not want to try on a factory ECM with a chip, not that I could burn a chip anyway.

Nothing is new here either. I did manage to replace the stock converter with a higher stall unit. I couldn’t build boost with the 60mm turbo at the line and had a 2.6 60ft with a 12.8@108mph.

Now I’ve got a Lonnie-Extreme Stage 2 with his 3,000 stall converter. ...and a Transbrake.

I’m hoping to get over there during a track rental if my work schedule permits.

 

[RmvBfrFlght]

Hey gang,

Someone told me that increasing injector duration can be done instead of increasing fuel pressure.

Is he right?

Thx.

Only up to the point that the injector duty cycle (DC%) is over 85. Once 100% is reached, that's it, no more fuel can be added. Inbetween 85% and 100% the injectors can get erratic in fuel delivery.

RemoveBeforeFlight

 

[NY Twin Turbo]

Ok,so I’ll tell the guy that it can work,but it’s really not the correct way.

As for me,I’ve got an Accufab FP reg,a chip burned by Eric and his 60lb injectors and a DW301 pump and Alky. I was actually one of the first “guinnea pigs” to install the DW pump when it first came out. So,I’m good.


I’ve just never heard of increasing inj duration to substitute rising fuel pressure for increased boost.

So why don't you tell your friend this:

It's a shame that Saab in their effort to reduce cost by leaving out a fuel pressure regulator has made it so difficult for you guys. Now you Saab guys have to re-vamp your entire maps and tunes to compensate for the absence of a fuel pressure regulator. And when you run boost way up you may even run out of injector pulse width to supply adequate fuel and even worse the equalization of fuel pressure and map may stop your injectors from flowing anything at all. If only you guys were as lucky as us and were just able to use a smaller injector that was easier to control during idle and cruise and not have to over size them. But then again you Saab guys shouldn't have to worry often about running out of injector because you need to make a lot of power in order to need more fuel and this isn't normally a concern for Saabs in general.

 

[HighMileage]

It's pretty easy to test if you run an ECU with FP correction and loggimg. Tell him to test it and report back.

My guess is there won’t be much left to test very soon. He just bought it and is on a quick quest for more boost.

 

[ScottHeidinger]

It's pretty easy to test if you run an ECU with FP correction and loggimg. Tell him to test it and report back.

My guess is there won’t be much left to test very soon. He just bought it and is on a quick quest for more boost.

He should leave it alone and enjoy it for what it is or sell it and buy something else, parts for those cars are expensive and their head gaskets will not take the added boost. The engine didn’t have any balls so they added a turbo to give it a little bump but it’s not designed for much boost at all. Many of them had issues with their fuel pumps so he should look into upgrading the fuel pump first if he plans to do any performance upgrades as we all know what happens when we run a turbo car without enough fuel. Even with a turbo they are very slow and the money spent getting the ECU modification might give him 20-30 HP and it will still be extremely slow.


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[HighMileage]

I sent him an email mentioning all input here on this thread.

I believe it was more than he bargained for.

He really should just keep it stock.

Thanks everyone for your input.

 

[Turbo6inKY]

I'm baffled by this entire thread.

This is basic physics.

Things move from areas of high pressure to areas of low pressure.
The rail must be pressurized to a point higher than the manifold or nothing will move when the injector opens.
For flow to to be predictable, the delta between the rail and the manifold must be the same at all times. That's why we have a pressure referenced regulator on the fuel rail. So that every time that injector opens, there's 43.5psi of pressure forcing fuel into the manifold.

There has to be a fantastic amount of bullshit out there for somebody to even consider what the OP is asking about.