Injectors

**Phlash_riot** · 10-22-2006, 09:17 PM

So what all the hub bub about fuel injectors. from what little i know there are no performance gains form them if you upgrade. From my point of view all i can tell is that you only need to get "bigger" injectors if your set-up is in need of a larger fuel supply.

At what point do you need to start looking at injectors? Can anyone make a small chart or something showing injector size next to max rated HP output?
When do you need to start looking at bigger fuel rails? Fuel pump?

What is up with secondary fuel pumps? Why have one at all. if you have them on the same fuel tubing going from tank to rails a secondary is going to be restricted by the limited flow of the in-tank version right?

What is a good pump to get (in tank replacement)?

Do the stock fuel pump "boosters" (all they do is up the voltage to the pump so it overdrives itself? ... ... killing its lifespan and reliability?) work OK?

Or does someone have a good site to recommend and i will do the reading.

**Killer_bluebird** · 11-04-2006, 07:59 PM

Basically as your engines power output it increases so will your fuel demands. Usually you want your injector's duty cicle to not exceed 80%. There are various calculators out there that you can use to match your injector requirement to your engines output. Most Large Cammed Cars or Head and Cams (with supporting boltons) will generally need bigger injectors to operate safely. The stock 28 # injectors support around 358rwhp @ 80% duty cycle. Where as 42 # injectors (popular size) will support around 537.6 rwhp @ 80% duty cycle. As far as fuel pumps go Walbro Fuel Pump 255L intank pump are very popular if you do a lot of racing and are putting over 450rwhp to the wheels although it will never hurt to have one if you are over 400rwhp. The stock fuel pump "boosters" all they do is provide better wire than what the stock setup had and help minimize a drop in voltage which will in turn lower the fuel preasure delivered by the stock pump. This could starve your engine of fuel while the car is in WOT (degrading performance or possibly damaging your engine). At least that is my understanding.

**Phlash_riot** · 11-04-2006, 11:21 PM

So can i have bigger injectors without needing them?

Could i put the 42# injectors on a stock engine and not have any issues? I know it would be a waste but will they consume more fuel? I wouldn't suspect to see a increase in HP just wondering if you could do it in theory.

**shady milkman** · 11-05-2006, 02:19 PM

Originally Posted by Phlash_riot

So can i have bigger injectors without needing them?

Could i put the 42# injectors on a stock engine and not have any issues? I know it would be a waste but will they consume more fuel? I wouldn't suspect to see a increase in HP just wondering if you could do it in theory.

its all electronic fuel ingect. so no it wouldnt hurt anything and the injectors would just be running at a lower percentage..so i assume if you get larger inject. you'll need to adjust something in the pcm telling it it has larger inject. but i could be wrong about that, i just know it wont be shooting out more gas/aka consuming more gas.

**ericwilloughby** · 11-05-2006, 07:54 PM

The pump boosters don't just have better wires. They step up the voltage to 17 or so driving the pump harder and faster. It works great but is about the same price as a bigger pump.

If you double the size of your injectors they will put out double the fuel if the pulse to them stays the same. Across the entire RPM and at every throttle position. The O2 sensor will see this as too rich and try to adjust it back down but the PCM can only compensate for about %15 or so which is pretty good actually.

A programmer like the Diablosport I bought last week will have a function for injector slope if it is worth a damn. You figure the % you increased your injectors and enter that into the program. The program then decreases the pulse to the injector so you get the correct amount of fuel at part throttle. I don't know what happens at WOT. But the programmer has separate fuel adjustments for WOT so either way you are good to go.

**ericwilloughby** · 11-05-2006, 08:13 PM

Originally Posted by Phlash_riot

So what all the hub bub about fuel injectors. from what little i know there are no performance gains form them if you upgrade. From my point of view all i can tell is that you only need to get "bigger" injectors if your set-up is in need of a larger fuel supply.

At what point do you need to start looking at injectors? Can anyone make a small chart or something showing injector size next to max rated HP output?
When do you need to start looking at bigger fuel rails? Fuel pump?

What is up with secondary fuel pumps? Why have one at all. if you have them on the same fuel tubing going from tank to rails a secondary is going to be restricted by the limited flow of the in-tank version right?

What is a good pump to get (in tank replacement)?

Do the stock fuel pump "boosters" (all they do is up the voltage to the pump so it overdrives itself? ... ... killing its lifespan and reliability?) work OK?

Or does someone have a good site to recommend and i will do the reading.

Just adding fuel does not make power. You have to have air too.
The chart would be a good thing to know but just a rule of thumb and if you are in need of injectors than you had better already have a way to richen your old setup and monitor it in the first place.
You need more fuel when the O2 voltage at WOT goes below .88
Then you richen it with a programmer or increasing fuel pressure.
Your injector gets maxed out when it is running at %100 duty cycle and to see that you also need a gauge\programmer. That is when you need larger injectors and a programmer to set the pulse to them.

Fuel pumps. The pump in the tank is not a restriction to a secondary usually. Unless the 2nd is just pushing really freakin huge amounts of fuel. I'd guess 2-3 times the amount of the one in the tank. Reason. The flow rate is rated at some GPM at some PSI. The 1 in the tank is no longer restrained by all that back pressure because the pressure is resting on the secondary pump making #1 capable of flowing much much more fuel than before. In addition to that, the sec. pump is no longer having to compress fuel from a vacuum to 50psi. The incoming fuel is being forced into the intake of #2. But instead of doing all of this buy a gauge and monitor the pressure. When it drops you know you need to do something about it. On my LT1 I took the oil sending unit off the block and put it on the end of the fuel rail. My in dash oil pressure gauge then was a fuel pressure gauge. Very neat looking and totally free. My GTO has a shitty oil light so I have no fuel pressure gauge. That bites.

The boosters are about the same price as a pump. I'd say the new pump would be better. If it fits in the bucket right. I think the stock pump is good for 500WHP though. Just gauge it.

**Phlash_riot** · 11-05-2006, 08:32 PM

Thanks for the input. Atleast now i don't need to get one if it's good to 500WHP. I am aiming for 400 RWHP so I am well under that margine then.

**ericwilloughby** · 11-05-2006, 09:18 PM

If we're talking about the fuel pump, move that oil pressure sender to the end of the fuel rail. It is too cool to turn your key on then see the fuel pressure go up on your new in dash fuel\oil pressure gauge. It's also cool to see what happens when you run out of gas. haha.. It doesn't just drop to 0 it hovers around 20 for a mile or so and you can limp to the gas station by pumping the acc. pedal. haha.

**FantaZGuy28** · 11-05-2006, 10:37 PM

Originally Posted by shady milkman

its all electronic fuel ingect. so no it wouldnt hurt anything and the injectors would just be running at a lower percentage..so i assume if you get larger inject. you'll need to adjust something in the pcm telling it it has larger inject. but i could be wrong about that, i just know it wont be shooting out more gas/aka consuming more gas.

I was talking to a guy about injectors this weekend and this is what he had to say about me and my 36LB SVO injectors. You can run bigger injectors w/o needing to tell the PCM. The computer in the car will still push out the stock injector size but if you get a h/c package or even a blower you can get it tuned for the injectors to spray more fuel. I have a s/c tune so the injectors are spraying the max amount for the injectors...but im going to delete my tune with HP tuner this weekend so the injectors shold trim down the fuel back to stock so im not running rich.

**ericwilloughby** · 11-06-2006, 03:57 AM

The injectors WILL spray more fuel. All the time, all the way through the RPM range and at all throttle settings. Until the PCM learns that it is too rich and will try to compensate. But you will run pig rich. If you change injectors you will need to tune it. Don't have too, just need to. $320 with a Predator. The computer doesn't push a injector size?? It sends a pulse and doesn't care how much gas is getting dumped in. Until the O2 is pegged on the rich side and then it tells the PCM to shorten the pulse. But it will only compensate so much.