So, if I wanted to get set up for future mods while increasing my power and not completely destroy my mileage... I could get tuned for 19lb injectors but install 24 lb injectors, so later on when I'm ready for a bigger cam and such I could just get retuned for the 24lb'ers?
Am I at least on the right track?

 

You are closer but still a little bit off.

You do not get tunes for the injector, period. If you want to get 24lb injectors, go right ahead, there is nothing else you need to do in order to run them.

If you get a bigger camshaft, THEN you will need a tune.

I don't know how to make it any simpler than that.

I think I might make a small explanation of injectors and camshafts on my site....

 

Ok, lemme try to work this out in my head... first things first... what tells the fuel injector to fire, and how much gas to give the engine?

 

Break down of how it all works...

Computer has a set amount of info. Among that information is when to fire injector, how much fuel to give, at what time the spark plug fires, blah blah blah. The computer controls the whole car. Think of the computer as the "brain" of the car. The "brain" gives orders to other parts of the car. Other parts would be the "organs" or "limbs/muslce" or whatever. I guess the fuel pump would be the "heart".

The "brain" (computer) says to the "heart" (fuel pump), "Hey fuel pump, I need this much pressure, and this much fuel." So now the pump gives out so much pressure and so much fuel.

Then the "brain" says to the injector, "hey, I need you to fire when I tell you to." So the injector fires (opens up) when it receives the command.

The injector is like a blood vessel. A human brain (not a car brain) cannot control blood vessels can it? Blood vessels are just there and work the way they were made. Injectors (car blood vessels) are the same way. They are just there and work the way they were made.

So now if you have a "brain" (car computer now) that is tuned to tell the "heart" (fuel pump) to give more fuel, all of a sudden the injector might go, "wait, I can't fire that much fuel in one cycle!" That is when the injector is too small and cannot deliver enough fuel. That is also when you need a bigger injector so it can deliver the right amount of fuel.

BASIC EXPLANATION: (talking about the human body now) The brain (computer) tells the heart (fuel pump) to pump this much blood. Heart then pumps that amount of blood. It has to go through the vessels (injectors). Now if the brain (computer) said pump a lot more blood, the heart (fuel pump) would do that, but the vessels (injectors) might be too small to travel that much blood. That is when a bigger vessel (bigger injector) is needed so it can travel the needed amount blood (blood=fuel).

Hope that makes sense.

Computer = controls everything
Fuel pump = pumps amount of fuel told by computer
injectors = opens on command (that's it, they do nothing else)

 

Ok, I think I'm getting the basic understanding of it.
Now lemme ask you this, and I'll give this thread a break for a few days.
How does the cam come into play in all this? Cam controls how long the intake and exhaust valves are open right? ... ooh wait, if you put bigger injectors, the car will run rich becaus it has more fuel than air, if you cam without bigger injectors, the car runs lean because more air than furl, so they go hand in hand?
Bigger cam = more air for more fuel from bigger injectors = bigger boom = go faster?
Hope I'm not being too much of a pain in the ***. Just tryin' to learn so I can come up with a better plan of attack.
Thanks for all the explanations.

 

Yes!

Just a few minor errors.

Not quite. Injectors do not deliver more fuel, the pump does that. If you cranked up the pump's pressure/rate of delivery, then yes you would run rich. Injectors alone do not cause cars to run rich.

To a point. If you run a cam without injectors it might be fine. The injectors might be able to give enough fuel without a problem. It will run lean if you run a cam, without a tune (if the cam is big enough).

Do not worry about too many questions, I like helping people.

Wow...I just re-read my posts and I can see they are not very good explanations. One last shot at this...

Do not worry about the specs here, just look at how close they are.

LT1 camshaft
intake lift: .447
exhaust lift : .459
duration
intake: 279
exhaust: 276

LT4 camshaft
intake lift: .476
exhaust lift: .479
duration
intake: 282
exhaust: 277

The LT4 cam is so close in duration to the LT1 that it will not make that much more power.
Not too much more power = not too much more air
Not too much more air = not too much more fuel
Which means the stock injectors would be fine. As far as a tune goes, the stock tune would also be fine since it does not need too much more fuel. Is it starting to click yet?

Computer tells pump, engine needs more fuel. Pump delivers fuel. Computer tells injector to open. Injector opens. Now if that injector cannot deliver enough fuel that is needed in that opening, that is when a bigger injector is needed.

Oh wow...I'm going to make a graph, I have an idea...

 

lol... ok that's what I wasn't getting. The pump does NOT deliver a constant amount of fuel... it's governed by the computer?
And the injectors only ALLOW the fuel from the pump to get into the cylinder when prompted by the computer?
And tuning = the computer telling the injector when to fire and how long?
So, 19lb injectors have the capacity of delivering 19lbs/hr of fuel, but only as long as the computer is telling the pump to deliver that much to the injectors?

 

So close!

No, it DOES deliver constant fuel. The injectors basically make the fuel wait till the computer says open. Yes it is governed by the computer, in a sense.

Yes. Injectors get told when to open by the computer

No, tuning tells the pump how much fuel to send. That is all tuning is. It is the injectors job to have the ability to flow the needed amount of fuel.

Yes, and no. Yes the injectors can only deliver 19lbs/hr AT MAX. No the computer does not need to constantly tell the pump to send 19lbs/hr. It can send less. If the engine needs more than 19lbs/hr, than you need a bigger injector.

Here is a very quick graph I made to show the relationship between injectors and horsepower. Notice how the more the horsepower goes up, the shorter the horsepower span is for the injector. Means; more horsepower = more fuel.

Here is the graph

Fairly accurate and easy equation for finding the correct injector size is;

flywheel horsepower x .073

400 x .073 = 29.2

29 injector is good to 420 horsepower.

EDIT: Check here for my very general description. Maybe it is better than everything I have given so far.

ShibbyZ

 

Ok, so I can see from your graph that:
1. My injectors are crap
2. 19lb injectors from a 3.8 are not too bad for an everyday driver with a little pep.

So, maybe this will help me understand a little better if we go to the other end of the spectrum... with a stock fuel pump, how would it affect my car if (hypothetically) I put 34lb injectors in it with the stock tuning? And then with it tuned for the 34lb injectors?
And since we're on the subject, could you do a semi in-depth explanation of what tuning is?
Man, I think I've learned as much about engines these last couple of days than I did all year!
Thanks alot.

 

You've just touch the tip of the ice berg. There is so much to the physics, math, geometery, and science of engines. But anywho...

Installing 34 injectors and getting them tuned for the engine, without doing a cam or anything, will not do anything. They will not add power, they will not make it faster, and the only thing it will do is make the injectors work less since they can flow more than 19# with the same opening.

Camshaft determines EVERYTHING! The bigger the camshaft the more gas it needs, along with more air. Bigger the cam = the more air, more gas, bigger stall, bigger injectors, more power, better tune, everything.

Ok, new approach. Think of the injector as a hose with your thumb over it. If you move your thumb back and forth covering the hose, it is like an injector. It is going to spray water out the hose when you let your thumb off. Now if the pump is told to send more fuel (by the computer), you are going to need to keep your thumb off the hose longer to get that extra fuel. That is called duty cycle, if you don't know what that is I'll explain that too. Now if the needed amount of fuel is so great you need to keep your thumb off the hose completely to get the needed fuel, that is 100% duty cycle. That is when you switch to a bigger injector, or a bigger hose. The bigger hose (injector) will flow more water (fuel) without having to keep your thumb off the hose as long.

tune explanation
Tuning is adjusting the air to fuel ratio. INJECTORS DO NOT DETERMINE A TUNE. Just need to make that clear. The camshaft determines the injector. Now say I go and get a monter of a cam, just the biggest one I can safely run on the street. That cam is going to need a lot of air to feed it, along with a lot of fuel. The tune is in changing the computer. You change the computer so now it realizes, "hey, I have one huge camshaft in me, that thing is going to need a lot of gas!" Well you measure how much air is coming in, then get it on the right ratio of air:gas. It is usually around 13:1. Now that the computer knows it needs more gas, it goes, "hey fuel pump, I need this much gas". Fuel pump pumps the fuel. Fuel arrives at the injector and the injector goes "hold up, I need to be open all the time to supply that much fuel!" (like keeping your thumb off the garden hose) Now you switch to a bigger injector that does not need to work as hard for the same amount of fuel (bigger hose). Now you have the ability to have the right air:fuel ratio.

Tuning is plugging into the computer, giving it new information on the changes made to the car, and adjusting it to optimum performance.

 

Man my posts are huge. Maybe some actual examples would do a better job. These are examples, not really hard fact!

Say I have a 245/255 duration camshaft (which is big). Now say it needs 100 cubic feet of air per cylinder (that is also a lot). It would need roughly 7.7 or so amount of gas per cubic foot. So the 100:7.7 = 13:1

Now say I have a tiny camshaft, 200/210 duration (close to stock LT1). Say that cam needs 60 cubic feet of air per cylinder. That's 4.61 for every cubic foot of air. 60:4.61 = 13:1.

Notice how the ratios are the same but the amount of fuel is different?

Now say 19lb injectors can flow up to 5.5 on the 13:1 ratio, so 19lb injectors are obviously not enough for the huge cam, but are enough for the small one. Now say I get 24lb which can flow up to 8. That would be big enough for the huge camshaft, and more than plenty for the small one. Since the 24lbs are bigger, they can supply more fuel. Basically the bigger injector has a bigger opening allowing more fuel in.

More clearification: the 5.5 would be a 71.5:5.5 ratio, 8 would be 104:8 ratio. So if the engine does not need more than 71.5 cubic feet of air, the 5.5 19lbs would be ok. If it didn't flow more than 104, 8 24lbs would be ok.

Again, those are examples, not real. I don't know how much certain injectors flow on a 13:1 ratio.

 

Ok, as an example, since I'm not real sure on my car... Now remember these are not even estimates, but numbers pulled outta my ***. These numbers dont even mean anything, just a quantitative measurement that my brain is happy with. I understand duty cycle, so in relation to that I'm going with the injectors flow as a measurement of time. (in seconds) Where 1.0 is maximum flow for the injector.
RPM / Fuel Flow with stock injectors:
1000 - .2
2000 - .4
3000 - .6
4000 - .8
5000 - 1.0
6000 - 1.0
7000 - 1.0
etc

Now with 19lb injectors
1000 - .2
2000 - .3
3000 - .4
4000 - .5
5000 - .6
6000 - .7
7000 - .8
etc

So with stock injectors I reach maximum fuel flow at 5000, but the 19lb'ers are easily able to accomodate for the demand.
Maybe?
And if you're worried about going over my head when speaking technically and scientifically, I understand techie. So no problems there.
Thanks again for bearing with me. I'm thinking that I just didn't realize there were that many variables when diving into this topic.

 

EURIKA! That's how it is, if you are refering to the first set being 16lb. But still,

 

Woo Hooooo!!!
Thanks for grinding it out with me man!