So I have noticed more of an interest in IDI injectors recently, and addressing the basics of them is starting to be a bit of a task.... So here goes...

Ive spent a decent amount of time trying to understand the IDI aspect of diesel engines, and specifically spent a bunch of time trying to figure out our injectors as they are...

I want to start a thread on all things IDI injector...

Our Particular Injectors came in the form of Stanadyne A, B, D, E, And G codes...

The Aftermarket comes in the form of G, BB, and (?)Blank codes...

In all of my testing, I haven't come across a code of injector that pops different from one another (Stock range being 1750-1900), Contrary to the popular belief that the G-codes pop higher.

Our injectors have a nozzle area similar to a "Direct Injection" injector with 5x.018" Orifices... And those are capable of flowing enough fuel for 800+whp...

This thread is meant to be the go to for all injector questions... If you have a question, ask away, and maybe we can get the info straightened out on these things...

 

Good info there, thanks!

 

So, if I understand you correctly, the injectors are the same on both NA and turbo engines?

Do any of the injectors have different fittings? X code only fits on Y year engines, etc?

 

I would really like to see what the spray pattern looks like on stock injectors and on higher pop pressure rebuilt injectors. From what I understand some things can be done to the pintle to get a more desirable spray pattern, what is done to the pintle?

 

I will get some pictures of the different parts of the different injectors. As soon as I find my charger for my Camera, I will get some video of different injectors, spray patterns, pop-pressures, etc.

 

Why are these injectors so "overbuilt" i guess i wanna say? Basically why did they put an injector capable of that much power in from the factory and then have such a limited IP?

 

I hope you find that charger, I am pretty interested to see the differences.



Hey, how exactly is a rainbow made?
How exactly does the sun set?
How exactly does the posi-trac rear end on a Plymouth work!?
It just does.

Just kidding, I don't know.

 

Hey i ain't complaining that our injectors can flow enough for 800+whp, don't get me wrong lol

 

I would like to know more on how pop pressure effects injection events, spray pattern and hot starting performance.

I know the nozzles on G code injectors are bigger as the protective caps from my G codes are too big for the BB code injectors.

 

ok i pulled injectors from 6.9/7.3 idi yesterday. 7 of them are marked cav england. anyone have any info on these?

 

Considering the small space of the prechambers and the method of combustion the IDI uses is spray pattern that much of a concern in comparison to direct injection?

 

IDI was partially developed so that lighter duty pumps could be used, lesser injection pressures, lesser loads on the system. This was the way to do it, by using a bigger injection nozzle, the whole system see's a lot less peak pressure. Because IDI uses a hot precup to blast fuel against to vaporize it, it doesn't need a finely atomized spray, and therefore can run a lot bigger nozzle.

 

As far as pop pressure effecting injection events...

Here is a Very Crude Ms paint drawing I did to show how it works...



Basically, you have a fixed frequency of events determined by the lobes on the cam ring. The shape of the event changes with the volume of fuel pumped, but the frequency stays the same. The drawing is showing a constant volume of fuel and what affect pop pressure has on its delivery. The incline of the cam lobe builds pressure in either sense, and that pressure is exerted on the fuel lines. If anybody has ever wondered why they are all the same length, this is why, they need to have the same internal surface area, so that there is an equal amount of expansion (and therefore consistent timing) between the lines. The fuel lines act as a cushion until pop pressure is achieved, and the injector opens. When the injector opens, the metered volume of fuel displaced by the plunger is injected (Grey Shade). Now you can see that Pop "b" is happening a lot closer to the bottom of the ramp of the cam lobe, as well as operating at a lower pressure. This means that the volume of fuel is injected over a longer period of time (Duration "A"). If you take a look at Pop "a", the pressure is raised, and the injector is opening closer to the top of the cam lobe, resulting in a much quicker injection rate, because the same volume of fuel is being injected in a shorter amount of (Duration "B"), under higher pressure. The difference in duration equates to a higher peak injection pressure as well (Peaks of the curves).

The idea is to tune the rate of injection (Depending on fuel volume at a certain "sweet" spot where you want your engine to operate at) for the most cylinder pressure over a given crankshaft angle. This is how we tune our timing.

Im not smart enough to figure out all the equations and tell you exactly where the best pop pressure for a certain amount of fuel at a certain RPM at a certain point of base timing is, this is where tuning comes in. However, I will say that our stock injectors are tuned for a very low fuel output, to inject over a certain crank angle and achieve full burn before the piston reaches BDC, That is why they burn so clean. But that is also why my stroked G-codes with a 2500 pop run like a stock IDI driving around town off boost.

Now that being said, I don't know if my injectors are set to their optimal spot, I need to tune it and see what different pop pressures do with the amount of fuel I have, but for the vast majority of us, a simple bump in pop pressure when running more fuel, keeps the burn ratio in check.

As far as Spray pattern goes, As I said above, we are blasting diesel into a Hot Inconel cup at a very fast rate, as long as the spray pattern doesn't effect rate of flow from the injector nozzle, it shouldn't effect burn rate... The exception would be too much of a stream in which the fuel couldn't be broken as effectively by the force against the hot pre-cup. The situation required for this to happen is almost non-existent, and if it did, you have bigger issues with the injector anyway.

As far as hot starting condition goes, yes, increased pressures can have a negative effect on it, which is the normal reason people start to have issues with a new set of injectors on a ragged old pump. Chances are though, if you have an old pump, and are having a hot start issue with it, its probably time to upgrade if you want to run more fuel warranting higher pop injectors.

And finally... No the nozzle area between the two different brands is for all intensive purposes, the same. You can actually run parts from either brand in either injector, that's how close these things are made to each other.

 

Delphi bought Lucas/CAV.... Those are just early BB code injectors. All the parts are the same as current Delphi injectors.

 

This.

As I said above, the fuel is atomized against the hot pre-cup--->fuel starts to burn and expand---->expanding gases push fuel out of chamber as it continues to burn, increasing velocity----->Chain reaction until all fuel is burned at the right moment, achieving the most pressure on a certain crank angle...

By the time the fuel exits the Pre-cup, it is completely atomized and vaporized... This is why IDI's run a bunch quieter than 12v's, consequently, while the start of burn is slower, the burn rate catches up, forming a more complete burn, which is why we can get away with a lot less total timing than a direct injected engine.