Question on injector pop-pressure

[Jl2019]

So we’re almost done with winter here in the mitten, and over the course of a few months, my injectors have slowly deteriorated. I could just order a new set, but if I did that I’d want marine injectors which is in my future plans anyway. But in an effort to save some money, I asked around and found a couple local diesel shops that will rebuild the ones I have for a lot less than the cost of a set of marines. I could just ask them to set the pop-pressure to factory specs, but since I’ve done a few modifications to gain some power and mpgs, I thought I’d try to come up with a number that would better suit my truck and possibly up my power/efficiency a little more.

here’s my list of air/fuel upgrades

-Wicked Wheel in a factory GM-8
-turbomaster set at 15 psi
-Air Dog DF-100 100GPH lift pump
-FTB mod
-3/8” IP inlet
-1/2” fuel lines from tank to valley
-Beans Diesel Sump
-Performance tune from Quadstar

There’s not a ton of info on pop pressure other than the recommended psi. That being around 2100-2200 psi. However I did manage to find an old thread on a different page of guys testing different pressures in the name of science. One of these mad scientists said he went up to 2800 psi and didn’t have any real issues. I definitely don’t want to push my luck so I was wondering if 2300-2400psi would be an option that would benefit my truck.

Any extra information on pop-pressure such as long-term effects of running a higher-than-oem spec psi, or improvements in fuel economy would definitely help.

 

[Will L.]

Welcome. It helps to fill your signature line with all of your truck details, so those people read your different posts we can always refer back to the individual situation. Also I realize a lot of people like don’t like to announce where they are on line. But sometimes That has relevance, as in this case...

Location, pop pressure??
Most all of the United States of America has different levels of mandated ethanol or methanol in their diesel fuel. But some locations like Alaska do not. When you have a blended diesel fuel that is part bio fuel this also comes into play with pop pressure.
This is because the different liquids change the viscosity of the fuel.
It also changes the burn rate of the fuel in the cylinder. Total btu per cc, etc.

if you look around on this forum I do believe there are/were members here that went well into the 3000 psi range,3200 iirc.

really with the new fuel the best thing to do just to get a basic pop tester, or build one, get 2 sets of injectors and a bunch of shims. One set in the truck So you can drive it and put some miles on it, while working on the second set. Do your own data log of 0- 60 time, mpg, drivability, how easy it starts. Once you go through a couple tanks of fuel, swap in the next set of injectors that are 100 psi higher and redo the same tests. Continue this procedure until you have found where are you want to be. Then put your second set at the same level and verify your findings. Now you can just drive it for the next 100,000 miles, and you have your next set of injectors ready to go for when they are needed.

Obviously you will have found YOUR sweet spot rather than what works good with someone else’s set up. The difference in a turbo will make that engine perform very different then someone who had an HX 40 or ATT. Yes having reference points from other people it’s always nice but unfortunately most of the reference information you’ll find was all done back when we had real diesel fuel instead of corn juice mixed into our crude. Too many variables.

it is a lot more work and more expense, which is why most people just take their best guess and throw set in after having brought up this topic, and most of the threads never have comparison information of different pot pressures. The most you usually find is people making commentary about it getting harder to start once the pressures get too high. Also information talking about how lower pop pressure allows more overall fuel into the cylinder, and the higher pump pressure causing a better misting and more efficient burn of the fuel For hire mpg and depending on their situation better power

If by chance you scour the Internet and find threads or articles showing charted results,
Please do share a link here. I had some years ago on paper, and unfortunately lost it all. But that was with the old fuel not the modern stuff. Best of luck to you in this endeavor.

 

[MrMarty51]

Nice truck.

 

[dbrannon79]

Welcome to the forum. nice truck too! iirc marine injectors for 6.5 trubo are set at 2300 psi and standard spec is 2150. Will is right, we all have learned a lot from him.

 

[Big T]

Just replaced a set of worn out marine injectors with a new set of Bosch (India) injectors from Leroy Diesel. Seat of the pants feel says the Marine injectors had a bit more hp, but they produced a lot more black smoke. It was enough that some Volvo driver at 6,750’ elevation reported me to the CARB violator site. I’m running these with A-Team Turbo and a Heath flashed tune in the ‘99 Suburban. Have not driven it enough to tell if there is a difference in mileage.

 

[jrsavoie]

I had good luck at 2300 psi balanced injectors.

 

[Rockabillyrat]

Pump output will determine your desired pop pressure. For a tuned DS4 stick with 2200-2300psi.

 

[JMJNet]

There were a lot of discussion on marine injectors in the other forum.
First, it is very difficult to get an original Bosch nozzle for marine, if there is, probably not cheap and it should not otherwise CKO.
Second, for some reason, this engine cannot handle marine from the limitation of other parts in the truck.

IMO, if you can find a local shop that can rebuild with a genuine Bosch nozzle and up to spec, I will do that instead of hunting for marine nozzles.
A properly build injectors beats any improperly build CKO marine nozzle injector.

JMHO.

 

[Will L.]

Back years ago I used to rebuild a lot. We ran regular and marine bosch in 6.5 on the streets. We tried some of the knock offs and had bad results. Having a larger volume of fuel is obviously useable by this engine- but when the nozzle doesn’t mist the fuel properly, there is just nothing you can do with it.

When I decided I was going to run them again and they were no longer available from Germany- I just waited and kept a frequent search going. it took me a long time, then when some came up, it was actually multiple sets of nozzles at one time. Sold off the others and kept 2 sets for myself. If I were to not do the bigger turbo and all that stuff I would just sell my German nozzles and buy the India Bosch standards. Then determine best pressure for them and run those.


If a person is going to stick with a stock turbo, going marine is a mistake. But when you have a better flowing turbo with exhaust, and a tune if ds4, or db2- then a 6.2 or 6.5 has no problem with the marine nozzles from Germany. If you are putting around at 1500 rpm - marine is a mistake.
But if you accelerate by 70% throttle- with the mentioned up grades, then the marines make sense. You will simple apply 60% throttle instead of 70%. The engine still does the same thing- it just acts as if you are pushing the throttle more because it is feeding slightly more fuel.
But the quality of the mist is very important.

Now that fuel has alcohol in it, that misting work will be more important not less. This Because the alcohols will ignite faster and have a faster flame front. And if the diesel left behind the alcohol now is slightly longer chain due to averaging. So images you get a quick partial flame going, then the rest follows and that second part is where the majority of your btu is at. A bad mist could actually cause two separate burns.

Then the other advantage of the marines is when you are going to raise the pop pressure really high. The higher pop pressure, that means the duration of the injector actually open becomes less. You have to push that amount of fuel out in less time. So if you want the same amount of fuel to come out as before, that pressure is higher- and higher pressure means you can create a much finer mist. This is key to newer systems- the much increased pressure for finer atomization of the fuel. But against- if that nozzle is not made absolutely perfect- it will just spit out the fuel as a liquid stream rather than misting.

The finer the particles are of anything the better the burn rate is and lower flash point. Most have heard of grain elevators or silos blowing up. Ever try to burn a piece of grain- it is because of the very fine dust that gets created. The grain has turned into an airborne mist.

So if you take the normal amount of fuel and get it to mist 20% better- your efficiency of burn improves. This will cause the flame to light and burn faster, so you must adjust timing accordingly. But also- it means there can be more time to burn a higher percentage of the fuel. The two bell curves of efficiency have an intersection point. Putting around simply wont work. But if you are actually working the engine, you wi produce the power quicker and therefore do it with more fuel efficiency. This is how the marine nozzles became more efficient in fairly stock trucks- the weight of the truck was enough to need the torque, and the drivers were accelerating frequently (city driving, hard). If a person were to drive like a grandma all the time- that would be more efficient. But when dealing with drivers that were constantly foot in it- they achieved that speed sooner and backed off the throttle sooner.
Getting the tune for the ds4 to support that use took time- and we had a guy that was good at it- definitely not me! Haha. We tried his tuning tricks with stock injectors obviously- but it was better with the marines. Now when there were drivers that took it easy or had empty trucks- those mpg gains quickly turned into losses.

 

[Rockabillyrat]

Keep in mind guys that fuel volume is controlled by the pump not the injectors. Adding marines to a stock engine does absolutely nothing other than shortening the duration.

As far as spray pattern, that is also useless on an IDI. Combustion starts on the prechamber walls. This is because the air velocity coming into the prechamber is so fast it forces the fuel to the walls. Doesn't matter what spray patter your injectors have the air velocity will force the fuel to the prechamber walls. Also once the engine passes TDC and the prechanber reverses flow, the pressure differential created by the cup atomizes the fuel as it leaves the prechamber and enters the main combustion chamber. Duration and flow rate are more important that the spray pattern in an IDI.

Im going to put the marine vs stock injector myth to rest on my test bench. I will have a full write up on that when it happens.

 

[Will L.]

Yeah, my explanation is the common understanding combined with results we got.
How it actually helped- I can’t really say. Same for when it hurt.

as to the misted fuel all going into the precup-
I know the better mist we got the more both power and mpg could improve.

I always guessed that either a portion of that mist was either shooting out the hole and the majority was getting spun in the precup, or the better mist made it spin and ignite better in the precup.

I remember watching videos from gm in the training class- but they were not actually video from inside- they were example videos- one showing inside the precup and another showing the flame front on piston- then another showing the 2 stage burn like in pre ignition or broken flame burns where it would ignite twice.

When you do testing of volume moved- would be interesting to see say 20 cycles of 1400 psi vs 3400 psi pop settings on a video.

 

[Big T]

Big Bear Lake elevation 6,750’.

Left: ‘99 K2500 4WD with Bosch Marine injectors, A-Team Turbo and Heath tune.

Right: ‘94 K2500 4WD with standard Bosch injectors, A-Team Turbo and Buddy adjustable tune on stage 4.

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Clearly the ‘99 puts out a lot more smoke.

 

[dbrannon79]

x2 I would love to see that write up. I have the old marine injectors and a set of standard ones that @Big T graciously sent me for attempting to rebuild. I haven't messed with them yet but do plan to post up some photos of them as promised once I get around to ordering or building a pop tester and when the weather gets nicer too lol. my headache with my rig has seemed to subside as I was getting a knocking that I think was ether a lifter or an injector. me not wanting to pour more money into an engine that is on it's slow demise.

but for it's condition, right now it's running really good purring like an old happy cat right now lol. that is what is keeping me from even opening the hood considering the last time I opened to hood the exhaust sprang leaks and made me thing I lost the vacuum pump. lately I have been tiptoeing around it saying nice things to it as I get ready to go somewhere

 

[Rockabillyrat]

I believe the biggest key to dial in injectors on an IDI is the flow rate curve. That is all determined my the pintle design and pop pressure. Because an IDI is a two part combustion process the injection needs to match. Stock and marine injectors use a throttling pintle to limit fuel at initial opening, then once the needle reaches full lift they flow more. The marine will out flow stock at full needle lift because of the pintle design. But only at full needle lift, they flow identically when they initially open. This I believe is key to making power and MPG in a IDI. You want a small amount of fuel to start the combustion process in the precup. Then a large amount of fuel as it reverses flow into the main chamber. So dialing in your flow rate curve to match the two part combustion process is key to getting your desired results. You need the right amount of fuel at the right time. So even though your fuel volume remains the same the flow rate curve and duration change between stock and marine injectors. This is where I think people feel difference when they switch to marine injectors. And again as you increase pump volume you need to adjust your injectors to match.

I plan to do testing with different injectors at different pop pressure and see its effect on volume and duration.

I have some pictures I posted on my precup thread that shows some of the combustion process. Our cups are like scheme 1 and 2.

 

[THEFERMANATOR]

If you read deeper into those old posts about increased pop pressures, many people in summer experienced hard hot starts with pop pressures over 2500 psi. I wouldn't run more than 2300 on a ds4, especially one with any miles on it.

 

[ak diesel driver]

My issue with even standard pop pressure is winter fuel having hard hot starts. EVERYTHING has to be in good working order

 

[MrMarty51]

My issue with even standard pop pressure is winter fuel having hard hot starts. EVERYTHING has to be in good working order

Does two stroke oil help any at all ?
Might probably take a bunch of it to offset that winter fuel blend.

 

[ak diesel driver]

Pretty much don't have any issues anymore. It just sucks when it'll work just fine on #2 but when #1 comes out it will find any part of the system that isn't up to snuff

 

[dbrannon79]

Does two stroke oil help any at all ?
Might probably take a bunch of it to offset that winter fuel blend.

I have run the walmart 2 cycle oil before as lubricant and didn't have any issues other than it turning the fuel blue! I am too curious if it really helped anything or was just a waste of money in the tank.

 

[MrMarty51]

I have run the walmart 2 cycle oil before as lubricant and didn't have any issues other than it turning the fuel blue! I am too curious if it really helped anything or was just a waste of money in the tank.

I told My nephew about adding some two stroke oil to his fuel.
He tried it, not sure how much He used. He said his old 12 valve cummins run more quiet and seemed to idle smoother with better acceleration. He is one of these perfectionist types and most products aint what they are advertised as, in his mind and most in real world, so if He thought the oil helped the I believe that it really did.