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Injector Nozzles

buddy said:
I really think of the problem being that you inject into higher pressure
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Injection pressure should be much higher than your cylinder pressure. I know mine is. The issue I see if you are right, is that it could hang the pintle up from closing all the way, causing fuel dribble/early pop.
 
nmb2 said:
Injection pressure should be much higher than your cylinder pressure. I know mine is. The issue I see if you are right, is that it could hang the pintle up from closing all the way, causing fuel dribble/early pop.
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But if the injector pops at 2100psi, then regardless, the first fuel coming out (or not if cylinder pressure is higher) is at 2100psi, even if the plunger pushing behind it will push it to 5000psi or higher. So what if youre running 40psi of boost with a 21:1 CR, at what point does your injection get over the 3500psi cylinder pressure while the pintle is opened at 2100psi not able to push the fuel out yet? I see this as quite an issue and fuel might heat up and want to burn at the tip. The injection event may only be 20ms, but that fuel pressure will have to ramp from pop pressure to final pressure. And what is that final pressure at what rpm and fuel rate? What if at 2500rpm and 100mm^3 it usually only hits 5000psi, then your fuel pressure to cylinder pressure ratio is still way lower than it would have been in a stock system that was never meant to go over the pop pressure. Its no wonder that GM increased the pop pressure from 1800psi on NA engines to 2100psi on turbo trucks. Because an NA truck will see 1000psi air pressure max at TDC, but with 15psi of boost youre looking at 2000psi, or under stock conditions of about 8psi of max boost, there would be a 600psi margin over pop pressure, just like NA had 800psi margin.

No one thought about maintaining that margin, except the guys that decided to go common rail so that fuel comes out at more pressure than youd ever have to worry about with even 100psi of boost.

Although I'd be willing to accept its a problem on the back end of injection as well.
 
Injection events are closer to 3-5ms depending on output and if you're using a DB2 or 4. I get what you're saying, and I'm not brushing it off my shoulder... I'm really thinking hard about it because its something I never thought about. Because of this, I intend on taking my stage-1's up from 2100psi to 2700psi and seeing if it makes any difference. I will certainly report back.

Also, since I've been so adamant about IH not doing pre-cups like GM did, therefore I don't think its an issue... here is something they both did. N/A trucks were 1800psi, and the turbo trucks were 2100psi.... so on that I can agree there is something to be said for that.
 
You'll notice one thing for sure, more diesel clatter at idle if you like that. And hopefully better combustion efficiency under load, less haze/smoke, lower EGT, better power, more mpg. Although its likely most noteable for towing, where youre loaded for long periods of time, especially on grades. Something a dyno might not show much difference, but real world use significantly impacted.
 
Got my marine nozzles ready to go back in. Only one was stuck. Psi is set at 3850. I used atf to pop test,less leaks,and lubes every thing real nice.
 
20 years ago, I used to add a gallon of ATF to the tanks of the old Mack once a week. The injection shop recommended it, plus its cheap.
 
Test drove with the 3850 psi Bosch marine injectors. It sounds and runs so much better. I could listen to it idle all day. Even starts hot.
 
buddy said:
But if the injector pops at 2100psi, then regardless, the first fuel coming out (or not if cylinder pressure is higher) is at 2100psi, even if the plunger pushing behind it will push it to 5000psi or higher. So what if youre running 40psi of boost with a 21:1 CR, at what point does your injection get over the 3500psi cylinder pressure while the pintle is opened at 2100psi not able to push the fuel out yet? I see this as quite an issue and fuel might heat up and want to burn at the tip. The injection event may only be 20ms, but that fuel pressure will have to ramp from pop pressure to final pressure. And what is that final pressure at what rpm and fuel rate? What if at 2500rpm and 100mm^3 it usually only hits 5000psi, then your fuel pressure to cylinder pressure ratio is still way lower than it would have been in a stock system that was never meant to go over the pop pressure. Its no wonder that GM increased the pop pressure from 1800psi on NA engines to 2100psi on turbo trucks. Because an NA truck will see 1000psi air pressure max at TDC, but with 15psi of boost youre looking at 2000psi, or under stock conditions of about 8psi of max boost, there would be a 600psi margin over pop pressure, just like NA had 800psi margin.

No one thought about maintaining that margin, except the guys that decided to go common rail so that fuel comes out at more pressure than youd ever have to worry about with even 100psi of boost.

Although I'd be willing to accept its a problem on the back end of injection as well.
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By the time cylinder pressure has gotten to 2000 psi you will be at full throttle and your injector pump will be making a lot more than 2100 psi!!! I'm not exactly sure what pressures these pumps are capable of but it's going to be quite a bit higher than 2000. So the pump has more than enuff pressure to push fuel out no matter what pop pressure is or what cylinder pressure is.....Even if pop pressure is 1800 and cylinder pressure is 2000 the pump is gonna force fuel out because it can make more pressure to overcome cylinder pressure. If i remember correctly max pump pressure is somewhere around 9,000 psi....
 
You will be at 2000psi from air pressure alone at TDC from just 15psi of boost and a 21:1 CR. Dont need to be at full throttle. The point is that yes we know the IP can push it out, but if it pops below the cylinder pressure is it going to be coming out clean or start melting injector tips. It just sounds really silly to have an injector pop at a lower pressure than the cylinder. If the injector pops at 2100psi then it pops when fuel pressure is 2100psi, which that pressure has to build from a plunger pushing it, and the first bit is still going to be coming at 2100psi. If it didnt make any difference then these guys wouldnt be noticing a difference, but it does.
 
I think the difference they notice is what it does to your injection duration. A faster cycle will help with higher RPM.

That being said, I pop tested my DPS stage-1's which were supposed to be 2100psi. 6 of the 8 were leaking internally, not causing performance issues I don't think, but enough to push it out of the fine threads... and my pop pressures were all between 1600-1700. I'm going to have the discs lapped back in to stop the leaking, and bring the pop up to 2300psi.

http://www.youtube.com/watch?v=sXW7vx0vgcg&feature=youtu.be
 
nmb2 said:
I think the difference they notice is what it does to your injection duration. A faster cycle will help with higher RPM.

That being said, I pop tested my DPS stage-1's which were supposed to be 2100psi. 6 of the 8 were leaking internally, not causing performance issues I don't think, but enough to push it out of the fine threads... and my pop pressures were all between 1600-1700. I'm going to have the discs lapped back in to stop the leaking, and bring the pop up to 2300psi.
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It could be that subjecting them to high cylinder pressure at low pop pressure contributed to the issue, if they were up to snuff to start with.
 
buddy said:
It could be that subjecting them to high cylinder pressure at low pop pressure contributed to the issue, if they were up to snuff to start with.
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highly unlikely. Its Ken being a con-artist, just like everything else he sold me, I have to fix it.
 
6.2, are those bosch's drilled to .042?

Side note, I was driving through IN last night past a Bosch plant. Got me thinking about seeing if they would custom set up a set of injectors, or would it be better, cheaper, wiser to just have a machine shop do the customizing instead.
 
I didn't drill these. I was drilling stock ones. Now that I know what psi to set them at I will try it again sometime. But for now the marine nozzles beat everything else I ever tried.
 
Ah, ok. Thanks. Do you think that the 3850 psi setting would be the optimal for most set UPS, or just yours with your timing and such?
 
If you idle and cruise at low RPM a lot, then excessive pop pressure could wear out the IP faster, so it might be a tradeoff. The IP wont build more than pop pressure at idle, because it so low of a volume that it doesnt necessitate more pressure, it just need to get it to pop. So by making it pop higher at idle and cruising around under 2000rpm at low fuel rates when it also may not ever reach 3000psi, there is more stress than normal. That, idle clatter, and similar systems is why I had recommended 2700psi max, and typically not more than 2500psi, 2300psi standard. If it turns out not to make a durability difference, after there are 50,000 miles on IPs with 3000+ pop injectors then I will absolutely reconsider my own recommendations. Its just an unkown.
 
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