jimbo1111

Many venders now sell chips that allow you to run with different injectors using the fqs. The way I understand it is that when you scale back the fuel with the fqs your scaling back the whole fuel curve. Wouldn't that just make the 55 lb injector look like a stock 36 lb injector or not? I can see how this would help with part throttle but when wot you wouldn't have the fuel you need. I have run 55lb injectors with afm chips and have seen the 02 sensor compensate for part throttle on it's own. Can someone shed some light. Thanks

mark944turbo

I dont think you understand the advantage of larger injectors. They are to increase the effective range of power that can be made with an engine. For example a stock injector will be open for 100% of the time when the car is using a certain amount of air, where a 55lb injector might only be open for 75% of the time with this same amount of airflow.

All the chips do is tell the injector how long to be open. The fqs does change the entire range, it lowers all the times equally. And this is what you want. It is not the same as a stock injector, because at a high hex value in the chip, the stock injector will out of its effective range, but the 55lb injector with the scaled back rating will be still be able to open and close safely.

Allowing the 02 sensor to accomodate for bigger injectors is not a good idea! You will surely be running too rich in open loop, no matter what boost you run if you are using 55lb injectors with stock chips.

jimbo1111

What your saying does not make sense to me. If the injectors are scaled back they will perform like 36lb injectors. If your looking for more fuel you won't get it. So what is the purpose of scaling back? It's good if your running stock fuel needs but if you need the fuel they will not deliver the fuel you need when scaled back.

OriginalSterm

they are not scaled to work like stock injectors as far as flow, they are scaled to work like stock for idle quality, yet still have the limit up top for more flow.

at idle with a stock injector you may be running a duty cycle of 10%, with 55 lbers you may idle at 7% with the same idle quality.

fast951

Jimbo, Running large injectors allows you to achieve 2 main things:
- Correcting AFR: Larger injectors allow you have the capability to flow more fuel. (if stock injectors are maxed out even with higher fuel pressure, this solves the problem assuming the chips are programmed correctly)
- Safety & Control: If you are running 95-100% duty cycle with the injectors, then going to larger injectors allows you will run them at a lesser %. When the injectors are at 100% duty cycle it is difficult (if not impossible) to control.

Scaling with FQS is just one method to handle different size injectors.

OriginalSterm

Dangerous too, running at 100% for extended periods of time may cause damage to the coil. The fuel flowing through the injector may not be able to cool it enough to prevent those tiny copper wires from failing and causing them to go open circuit.

jimbo1111

I understand but when you scale back using the fqs your affecting the whole range. When scaling back 55lb injectors by 37% your making them run at 36lbs through out the whole rev band. I am not adding fuel pressure control into the equation. If a chip is made specific for 55lb injectors this is a different story. The ability to run the injector correctly would require a completely different fuel scale on the main chip maps. This would be what I'm looking for.

fast951

Jimbo, it sounds that you need a chip designed to match your unique setup. Or you can get a chip with enough flexibility in it to allow you to get ideal AFR and fine tuned with a PB.

slivel

I'm sure someone elles can offer a better explanation, but try this: first you have to look at the MAP. Assuming it was designed to support higher than stock boost levels (and therefore power production), it has to increase the duty cycle of the stock injectors to an unacceptable level. By selecting a MAP for 55 lb/hr injectors the same MAP profile can be executed but the injectors run at a lower duty cycle. The critical assumption here is that the chip designer provided proper fuel and advance settings throughout the rpm and boost range to keep the mixture happy - not too lean and not too rich and not too much spark advance.

Jfrahm

What you do not understand is that the range extends farther up for the bigger injectors.
with 36 lb/hr injectors there is a point where they cannot deliver more fuel and that point is reached with larger values still in the chip programming. With 55 lb/hr injectors the lmit is not reached until the values get much higher. The trick is that the values in the software exceed the capabilities of the smaller injectors but not those of the larger injectors.

-Joel.

jimbo1111

For us to run 55lb or larger injectors correctly we need a specific chip. Scaling dose nothing because when you need more fuel up top you have to resort to increasing fuel pressure or re scaling the piggy back to a large voltage witch will shorten the maf hp potential. I have run 55 lb injectors with 36 lb maps witch seems to be the best way because the o2 helps with every situation other than wot. In this case the maf meter dose not max out prematurely. Because I'm using a load based program wot and part throttle never cross voltages. So one doesn't affect the other.

Tomas L

Jimbo, scaling fuel with the FQS or by canging the map will accomplish exactly the same thing.
It's not that easy to explain but I'll try.
Fuel amount to be injected for each revolution is a little simplyfied calulated like this.

Injection time = "measured amount of air during a revolution" x "fuel map value" x "FQS correction"
The amount of fuel injected is then:
Fuel amount= "Injection time" x "injector size"

If you have an injector that is to small then the injection time will be longer than the time for an engine revolution. The injector "bottoms out".

When you change to larger injectors you still have to inject the same amount of fuel for each pound of air. This means that you have to either lower the fuel map values (all of the have to be scaled down) or easier change the FQS correction factor. The gain with the bigger injectors is that the injection time value will be lower and will hopefully stay below the time availible during a revolution.

The point to understand is that the injection time is calculated from map+FQS values and the air flow. With to small injectors this calculated time will reach a maximum allowed value and can't get any larger after that. With larger injectors you can stay below this maximum.

Tomas

awilson40

Jimbo, what you are saying is correct...by scaling the fuel delivery back for larger injectors with the FQS you are delivering the same amount of fuel as the stock injectors at the same point in the map...be it Pt throttle, idle or WFO.
What this gives you by running the larger injectors is more 'head room' for more fuel on top if your set up requires it.
Take my car, I'm OK with stock injectors as I'm not at 100 % and I'm not lean in the upper RPM.
Now, If I were to add a MAF and/ or a larger turbo, then I would be lean on top and no amount of adjustment would help because the injectors are flowing all they can.
Hense the need for larger injectors, scaled back so I would have more head room to add fuel in the upper rpm ranges where I would need it.
So you really have to do both, scale back and adjust on top if required.

jimbo1111

awilson40 how will I get more fuel up top if my 55lb injectors are scaled back. When the duty cycle is 100% and the injectors are flowing 36lbs? With this theory I have a good part throttle but no more fuel to support the big *** turbo under the hood.

Tomas if I read you correct your saying that the fuel curve is linear. I don't buy that neither because many tuners have chips that change the fuel curve in certain areas. My ape has a different fuel curve than my stock chips.

For a chip to be 55lb injector specific It has to function like stock in the lower rpm, most part throttle and supply the proper scaling in the wot maps. Can this be done?

awilson40

the injector are not at 100 %, thats the point...If you were running stock injectors at 100%, then scaled back the overall fuel delivery to match up to the 55 lb injectors then the same fuel would require less injector time so they would be at 75% (or somewhere around there, I dont know the eact amount)
So then you could change the fuel maps to deliver more fuel. I'm not sure how it would work with a piggyback controller as I do all my tuning in the chips.