So I had an issue with an injector during my cam swap. While I was installing my pump and lines, I stripped out an injector body...

While being an annoyance, that isnt the point of this thread, the stripped threads have nothing to do with the function of the injector... However, I had to pull apart the injector to swap bodies with all the "working" parts...

First thing I noticed after pulling the injector out, was the carbon build-up on the tip, and its corresponding pattern... It wasnt even around the orifice... Now at first I thought that it might be because of the swirl in the Pre-chamber, but as I thought about it, I dont think with all the turbulance in the chamber, that carbon could build like that in that spot, it has to be because of spray pattern... (I wont know until I test them on a pop tester)... So I pulled the injector apart. I was suprised to see what the pintle looked like... It was almost like it was burned, or got "hot"... Only explaination I can come up with, other than it being screwed to begin with, was 6.5* of timing and 150cc's or fuel, and the cylinder pressure pushing the combustion back into the injector, because of too low of a pop pressure......dunno... However, Im pretty sure that the stg 1 injectors ken sold, were not a precision product, and that the pintles were probably not cut properly... Probably most likely on a bench grinder. As a machinist, I know that this can lead to a non-perpendicular tip, and probably why Kens injectors are so hit and miss... I like the idea of the DPS injectors, because it does make sense, however, A) the pump is going to get whatever amount of fuel it pumps past the injector no matter what, and B) if you dont have the right machining practices, its going to result in poor performance... I think that DPS injectors could be done the right way, and I just might experiment with that here... Well see.

Anyway... Here is some pics...

 

Wow that is a lot of carbon! You should make your own injectors. That would be cool to see. At a minimum, would you increase the pop pressure?

 

Yeah after only ~20K....

I think pop pressure is really setup determinant... So yes, as long as it was needed...

 

I'm with you on that it is based on the setup. I do think with the Db4, it is definitely beneficial to increase the pop though. Just more based on the fact that a Db4 pushes fuel in at a higher psi.

 

So what did you do, take parts off and old injector to repair that injector? I'll have to look at my old injectors to see if the tops are interchangeable. I'm thinking thats what you did?

Chet

 

injector internals...



racin you need to build a pop tester

 

that build up is nuts. Mine were not like that.

As for the bluing on the pintle, all I can think of is that it was either sticking open, or pop pressure was low enough that it was allowing combustion pressure to open it up. Maybe both.

 

Yeah, I cant wait to open the rest of them up...

 

Man those things look quite simple! I thought there was more to them. Guess not!

 

just grab some new quality stanadyne G codes like i did.dang nice injector.
dunno anything about them other than they sure work much better than the current NFL replacement refs lol.

 

Ya those refs are horrible. Lol.

A friend of mine actually talked to an injection shop guy who swears that G codes are the best. Especially when run with an IDI turbo pump. But I still believe that there is power to be had with modded injectors, especially at the power levels both Racin and NMB2 are at.

 

This is what you get when "Every one gets a fair shot and pays there fair share"

 

This is how I feel about injectors. Simply, the only way you are going to improve any code injector, is to open the orifice to flow more fuel, or cut the pintle out of the way. The stroke, without seriously modding things, is constant depending on shim stack and volume the pump is putting out at any given time. Now with that being said, you simply dont need to increase the flow because the fuel is getting through anyway, even with stock pintles... When we start breaking input shafts because the pump is flowing beyond what the injector will in the same amount of time, then its time to open up the orifice/cut the pintle, until then, it makes no difference, except for atomization, which is moot in an IDI anyway. Atomization for combustion, the part that makes the engine run happens post pre-chamber, and all atomization does within the pre-chamber, is either light the mix faster (more atomization) or slower (less atomization), both of which can be controlled by timing the pump accordingly. There is no proof that atomization from the injector itself does anything, there is a lot of people that say "YA, its SO much better" but I have a feeling that the plecebo effect is alive and well... There is no dyno numbers that prove anything, but I do see a lot of similar setups with different injectors making all about the same power... If you think about it, the IDI engine was developed because of this reason, low injection pressures and un-precise spray patterns could be used effectively... Thats why atomization makes such little difference...

XLT, my next set of injectors will be just as you say, a new set of G-codes... Maybe a set of BB's... Either way, they will get a decent pop, and thats it...

 

I know even a 12v Cummins is DI but why do they gain power from extrude honed injectors? I would think we gain the same benefit. I have started looking for some info on modded idi injectors but that type of info is few and far between. If I find any info I will share what I found.

 

Specifically because it is DI. They have to have a perfect spray pattern for complete combustion, not only that, but injector depth has to be set according to the advance, and all sorts of little tweaks... We all know DI is superior, but its all a give and take, you have much more precise fuel events to deal with...