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Injector Nozzles

Mercedes sets them to 135 bar,which I think is 1950 psi. I still didn't decide what psi to set them too. I might be able to get a little more fuel from the fairly stock ip at a low pop psi. GM went from 1600 psi na to 1950 psi turbo. So if I'm running 40 psi boost I should have 3200 psi injectors ?
 
Just dawned on me the nozzles in question are from the 5 cylinder motor, duh. I have 3 of those in the family, sister has two and her eldest has one. But any hoo.
I am thinking out loud that a longer opening time indicated by the pop test combined with the greater output per cylinder of the 6.5 has me wondering if the engine will be rpm limited any more than it is now. Since you have a limited amount of time to get all the fuel in there. I know with gas engines some at high rpm start injection before the intake valve opens .

But the longer opening time could also mean lower peak combustion pressures, quieter and easier on the parts. Can't wait for the test run results. :drama:
 
Also thinking outloud and correct me if I'm wrong (sure of that), but if your dumping 100 psi vs 50 psi of fuel, with a stockish pop pressure, how would that affect engine rpms? Do you mean like a torque band, so to speak? Or top end rpm being reduced? Definately sounds like if you squirt 2X the amount of fuel, regardless of pop pressure, you should get more HP. And if you increase the pop pressure, wouldn't that force a finer mist (right term?) which would promote more HP and efficiency?

Then again, I've been known to mis-interpret what others have said before
 
I decided too drive the vehicle with stock injectors first,that way I can compare. We had it running tonight,but not driving. The injectors seem to be in average condition. It sure starts hard though.
 
The used injectors started knocking pretty bad,and getting a random missfire when cold. I built the Monarks tonight with 2400 psi pop pressure,hopefully will get them installed tomorrow.
 
Bump that pop pressure to 3000. I can only say this- more power, less smoke, and LOUD exhaust.
Oh, and over 20mpg with 4.10 gears on strait wmo!
 
Starts better than ANY other 6.5 I ever saw. Hot or cold. Has a rattle similar to a cummins. A beautiful sound!
My next set is set at 3200. Going for max atomization. My experience has been- less smoke, more power, and obvious fuel mileage improvement. This is a db2 with the screw turned in, on a 94, with a gm8. Otherwise it is stock.
 
Got the injectors in. It runs smoother,and idles without shaking. Power seems the same,but less snappy . A little more timing should help. Kinda wish I would have left the pop pressure at 1600 psi.
 
ak diesel driver said:
I would think it would be more fuel
Click to expand...

Wouldnt that depend on the nozzle design and how much pulse width there is per injection? My understanding is that the lower the pop pressure is on the injector the faster the injector "opens" and starts spraying the fuel because it spends less time building pressure to open. Am i wrong?
 
Woody35 said:
Wouldnt that depend on the nozzle design and how much pulse width there is per injection? My understanding is that the lower the pop pressure is on the injector the faster the injector "opens" and starts spraying the fuel because it spends less time building pressure to open. Am i wrong?
Click to expand...

Sounds logical enough.

My bigger concern would be the effect the lower pressure has on the "coarseness" of the injection event and the ability of the "swirl" in the precombustion chamber to expose sufficient amount of fuel surface area to available oxygen. Basically, bigger "droplets" = less surface area.

I would also be concerned that if the fuel pattern it too coarse, a greater quantity of it may impact the precombustion chamber wall and also not be properly exposed to the mixing process. It may be fine because of the temperatures the precup operates at (vaporize the droplets) or it could possibly "quench" the precup and reduce the operating temperature thus impeding it's intended function. There's also a concern of increased localized quench effect on cracking o the precup itself. They all seem to crack anyways, I would be concerned about it exceeding the oe in service crack limit prematurely.

While I have not tried it myself, I would guess that probable events of too low an injection pressure could be inefficient burning, increased smoke and decreased power in addition to a possible unknown advance in injection timing ( as small as it might be).

With the nozzle open sooner, you may potentially end up with more fuel in the chamber but the inability to burn it efficiently.

My concern with significantly higher pop pressures would be potential wear on the ip components. Although, I don't have sufficient knowledge of the internal operation of the pump to say if that is a valid concern.

Just a few of my musings on the subject...

:)
 
Woody35 said:
Wouldnt that depend on the nozzle design and how much pulse width there is per injection? My understanding is that the lower the pop pressure is on the injector the faster the injector "opens" and starts spraying the fuel because it spends less time building pressure to open. Am i wrong?
Click to expand...

One thing to keep in mind is the inj is purely mech and doesn't care about pulse widths and such. If it opens sooner and closes later that has to translate to more fuel. It maybe only a minor amount but should still flow more. I've heard of guys lowering the pop pressure in their 1/4 mile trucks. All the issues GW talked about must certainly be considered when doing this
 
ak diesel driver said:
One thing to keep in mind is the inj is purely mech and doesn't care about pulse widths and such. If it opens sooner and closes later that has to translate to more fuel. It maybe only a minor amount but should still flow more. I've heard of guys lowering the pop pressure in their 1/4 mile trucks. All the issues GW talked about must certainly be considered when doing this
Click to expand...

AK makes a good point.

Pulse width on the ds4 is determined by the PCM and actuated through the fuel solenoid.

Timing may be slightly advanced, but I have no idea if the amount of advance due to lower pressures would be of any practical significance.

I change these things through a PCM reflash...
 
The more i think about it the more that does make sense. Im very curious about these different nozzle designs and if they would produceany significant power than stock nozzles.
 
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