Pop pressure test with dyno results

[n8in8or]

Ok, so I'm about 10 months late posting this info, but after seeing a conversation regarding this topic pop up on another thread I felt it was appropriate for me to share this info. I am trying to post this during my lunch hour, but if I don't finish I will just post what is complete and finish it at my next available moment.

Background: I went to the dyno Feb 10 2017 to see what my combo was putting out. In case my signature changes in the future my combo at the time was: 2004 Optimizer with home-ported heads, +.010 gaskets, -.010 pistons (~19:1 compression), Harland Sharp 1.6:1 roller rockers, homemade passenger side tube header, CKO HX40 turbo with Turbo Lab wheels, water-to-air intercooler, 4" exhaust, Raptor 100 lift pump and an Omega Plus Moose pump making 122cc of fuel at 3500rpm and Bosch marine injectors set to 2500psi pop pressure. I have attached the dyno charts from that day. Here is a video from the cab during the run.

During the summer of 2016 I had some hot start problems. To address these I got new batteries (I already had 1/0 battery cables) and installed a Power Master starter. The batteries didn't really help much; the starter did improve the problem due to the 30 additional cranking RPM, but didn't cure the problem. Conversations with Conestoga Diesel led to the conclusion that the high pop pressure was at least contributing to, and probably causing, the hard hot start problem. So after my dyno results I thought it was a good time to try lowering the pop pressure in anticipation of the summer of 2017 plus see if there was power in lowering the pop pressure. Conversations with Conestoga and Justin from R&D IDI plus some additional reading on the interwebs indicated there was some power to be had by lowering the pop pressure - due to the pressure/volume relationship (Boyle's law). This made sense to me and I was excited to try something that would not only improve my hot starts but also get me more power! So I decided to re-pop my injectors myself since I already had a pop tester that I had purchased while trying to diagnose some previous rough running. After considering all the info I had available to me, I decided to shoot for 1750-1800psi. Yes, this is lower than most people choose for an NA IDI, let alone a turbo application, but both Conestoga and R&D choose this pressure for their injectors which are intended for turbo applications so I figured I might as well go big (or little?) and try it.....let's really make it an experiment! So I went for it. Now I will admit that I'm not 100% confident in how accurately I was able to match the injectors to each other because the gauge on my tester is air filled and tends to chatter when popping injectors. I had to take my best stab at it and see how it went. Here's a video I took to show another guy the process. Note that I am popping the injector into the atmosphere.....in the future I will be adding a reservoir to pop into so I don't coat my lungs with diesel.

I went back to the same dyno Apr 21 2017. So what were the results? My butt dyno told me that it was an improvement. Take a look at the attached dyno charts and see what you think. Even though I changed the pop pressure 700psi, there was little to no affect on the power. Any discrepancy between the runs can be attributed to testing inaccuracies and the fact that I was at the point of changeover between winter blend and summer blend fuel (btw I run Stanadyne Performance Formula to the recommended ratio in every tank of fuel). Pretty shocking results I think (oh and more proof that butt dynos lie).

I will say that when I went to the lower pressure 2 other things happened: 1. the idle is a bit rougher. I gained a dash vibration that I didn't have before and you can feel the engine shake at idle most of the time. 2. The engine has become quite cold-blooded - below 50*F it will blow white smoke, with the volume and duration increasing as the temperature decreasing. Below 30*F it runs quite rough until I load it and get some heat into the precups. This isn't really what I want in a daily driver. I intend to re-pop the injectors again.

My next step: I have a good set of non-marine Bosch injectors that came with my Optimizer. I would like to pop them to somewhere in the middle, like 2100-2200psi and see what happens. I believe right now that there is little-to-no power to be had with pop pressure changes....now there are idle quality and perhaps efficiency/mileage changes (I haven't verified), but nothing really to be had in power. When I do this test I will go to the dyno once again. I am interested to see if Marine injectors make more power or not - I have yet to see PROOF that they do.....and it sure seems that a pump that puts out the volume of fuel that mine does would surely show whether they do or not. If I put in the standard injectors at a middle pressure and again see no change in power, then I will feel pretty confident that Marines don't gain much - again, as far as POWER goes. If I do lose power, then I will re-pop the Marine injectors to the same pressure as the standard injectors and hit the dyno again. This should give pretty conclusive results. Note that before I pop next time, I will be getting a quality liquid-filled gauge so I can achieve more accurate results.

I think that's it for now. I'm interested to hear comments and if I think of more info I will be sure to add it.

 

[JayTheCPA]

When I went from the 'Marines' back to OE (at ~2,550 pop), the difference was noticeable in terms of throttle response. The OE's are noticeably more responsive. Another noticeable difference was that the truck belched a lot more at start-up with the marines than the OE's.

No idea on power difference as that will come later when I hit the dyno again. Although, not sure how to tell difference in power from marine versus OE injectors in the Burb as I also swapped out the tranny since the last run.


Toward marines making more power, had read where they flowed a little better within a very tight RPM range. OE's were noted to flow better across a wider range. So, from a standpoint of only knowing what I had read, neither really have a power advantage over the other; it was just a matter of where in the RPM range.

 

[Will L.]

It could be you are pushing so much power that the pop just doesn’t alter as much as it does for lower power engines. As if the gains are fixed levels and not linear. My gains became limited, but really can’t remember at what levels.

Also could be that you are at two low sides of a bell curve. So there may be more you can pickup there. But having a few sets to swap out and dyno is what it takes to see.

Going from marines to regular at different pressures won’t give a level comparison, but I get why you want to try it.

Back when I did all my comparisons it was easier becuse I had 4 sets to try. So it was 1 day test, then night time reset all 4, and next day 4 more tests. Spending a week we realy nailed peak. 2350 became my go to spec.

But I am really thinking that the thinner fuel we all run now compared to back then throws the spec off. Really wish I had a couple gallons of the old stuff to do comparisons. The math I come up with so far shows about 10% variance with 5% ethonal biofuel- kinda huge.

Marines imo are really helpful at sustained high rpm. Boat(duh) or hummer gearing crusing freeways at 2,900 rpm. Having a monster ip makes up for the normal orifice injectors. I couldn’t run large injectors with my built ip until I added propane to help burn the excess fuel.

Really wish there was extra money to play with and could send extra injectors your way to build a set every 100 psi to build a bell curve, then tune from there. The top 300 psi is a fairly flat top of the curve, but hit a decent peak better at 2350 for me than 2300 or 2400. We actually did 25psi increments after seing nicer results at 50 than we did at just 100. Really need a GEP sponsorship here!

 

[ak diesel driver]

I have some "old" fuel. Too bad I'm so far away

 

[n8in8or]

Also could be that you are at two low sides of a bell curve. So there may be more you can pickup there. But having a few sets to swap out and dyno is what it takes to see.

Going from marines to regular at different pressures won’t give a level comparison, but I get why you want to try it.

Yeah I thought of that, that I could have swung too far the other way. And you’re right, I shouldn’t introduce 2 variables at once for my next test, but my main motivation is the ability to set up 1 set of injectors and do a swap in the shortest amount of time. By doing the marines off line I can back into a 1 variable test while also learning about the difference of standard vs marines.

Do you have any of your old dyno graphs anymore?

 

[Will L.]

No. I had a few peak ones, but those got lost in a move- think I was mad, should have seen my wife. That was the “important box”. Car titles, wedding pictures, etc. yeah, bad day. Went back into traffic on I95 next day and found couple odd pics including our framed wedding pics and the original marriage license. Git lucky to find those. Did I ever mention I am not too smart sometimes, like days with a y in it?

 

[n8in8or]

No. I had a few peak ones, but those got lost in a move- think I was mad, should have seen my wife. That was the “important box”. Car titles, wedding pictures, etc. yeah, bad day. Went back into traffic on I95 next day and found couple odd pics including our framed wedding pics and the original marriage license. Git lucky to find those. Did I ever mention I am not too smart sometimes, like days with a y in it?

I’m glad you found some of the really important stuff. I sure would have loved to have seen that truck in action.

 

[n8in8or]

It could be you are pushing so much power that the pop just doesn’t alter as much as it does for lower power engines. As if the gains are fixed levels and not linear. My gains became limited, but really can’t remember at what levels.

Also could be that you are at two low sides of a bell curve. So there may be more you can pickup there. But having a few sets to swap out and dyno is what it takes to see.

One of the things I neglected to mention at the start of this thread is this: INDIVIDUAL RESULTS MAY VARY. You bring up that point in your quote above. What I am seeing power-wise with different injectors is just my personal results with my unique combo of parts. It would be interesting to see the results at different power levels.

Back when I did all my comparisons it was easier becuse I had 4 sets to try. So it was 1 day test, then night time reset all 4, and next day 4 more tests. Spending a week we realy nailed peak. 2350 became my go to spec.


Really wish there was extra money to play with and could send extra injectors your way to build a set every 100 psi to build a bell curve, then tune from there. The top 300 psi is a fairly flat top of the curve, but hit a decent peak better at 2350 for me than 2300 or 2400. We actually did 25psi increments after seing nicer results at 50 than we did at just 100. Really need a GEP sponsorship here!

I didn't realize you had done such thorough testing on injector pop pressure. From previous posts I thought you just did seat-of-the-pants and economy testing on the fleet vehicles to come up with the 2350 number. This is very interesting. I'm concerned about how close 2350 is to the 2500 that I was having hot start trouble with before and because I'm not interested in changing injectors any more than I have to I think I'll stick in the 2100-2200 range for the next set. It would be nice to have a bunch of sets of injectors ready to go and do some testing. I wish I had made my header with more clearance for injector replacement - currently I have to remove the turbo to have enough access for the injectors and there is that one bolt that is a royal PIA to get to that I dread every time I have to remove it.

 

[n8in8or]

When I went from the 'Marines' back to OE (at ~2,550 pop), the difference was noticeable in terms of throttle response. The OE's are noticeably more responsive. Another noticeable difference was that the truck belched a lot more at start-up with the marines than the OE's.

Interesting. What pressure were your marines popped to? I wish there was a way to quantify throttle response, I feel like that could be subjective. Perhaps boost gauge videos from a standing start? Ambient temp should be included too as that affects the response of mine quite a bit (much more responsive in cool, dense air than hot, thin air).

 

[JayTheCPA]

While we are kicking-around thoughts . . .

From a theoretical standpoint, changing the pop should also come with an adjustmen in the tune. The way I see it is that by changing injectors with different pop points (and nothing else), the ones with the higher pressure will flow later in the rotation cycle. So the timing probably needs adjustment to match the pop pressure.

From a practicality standpoint, am fairly (to highly) confident that 6.5 tuners do not make any changes based on the injector's pop though. I did have one tuner concede that theoretically the timing should change, but nobody ever tested for this.

What pressure were your marines popped to? I wish there was a way to quantify throttle response, I feel like that could be subjective.

The marines were 2,100.

And need to revise my current OE pop: 2,250 (Apologies for the typo). They came that way from Leroy and I left them alone.


Observation is from seat feeling versus foot input. All other things remaining equal, I just had to replace the whole injection system and installed OE injectors. Previously I had the marines. Same tune.

With the marines, at start-up the truck left a black belch (the PCM commands 100% power when cranking). With OE, it still burps, but not anywhere near the coal type belch with the marines. The coal belch was definitely a marine thing.

In terms of throttle response, with the marines the truck felt just a bit sluggish as compared to OE. For the same throttle position, the OE's in the lower power request and RPM range feel that they are pushing the truck better than what the marines did. And, the motor responds more quickly to the throttle movements with the OE's.

 

[WarWagon]

While we are kicking-around thoughts . . .

From a theoretical standpoint, changing the pop should also come with an adjustmen in the tune. The way I see it is that by changing injectors with different pop points (and nothing else), the ones with the higher pressure will flow later in the rotation cycle. So the timing probably needs adjustment to match the pop pressure.

From a practicality standpoint, am fairly (to highly) confident that 6.5 tuners do not make any changes based on the injector's pop though. I did have one tuner concede that theoretically the timing should change, but nobody ever tested for this.

Theoretical?, Uh No. The timing has to be advanced significantly on DB2 pumps. I have around a 1/4" advance off the line to line marks for several (3) pumps now. The gears I just installed eliminate the chain stretch factor. This is just to clear the white unburned fuel smoke after the initial startup. I had to time by ear with observation of cold white smoke going down the road (idle-light throttle), excessive rattle hot, and checking for glow plug erosion. This advance was consistent even when the hi-pop injectors were fresh.

I am really interested in how they start with higher pop pressures. I likely have a injector longevity problem compound by running krap "gravel screen" Wix fuel filters and B99 now and then to attempt to pass emissions. Come to think of it I didn't always have such a horrible time with white smoke on startup like I do now.

I may be the only one who has "measured" emissions to pass. This is another angle to look at because patch has only officially failed once due to loss of pump timing at high RPM and white smoke. Frankly the other times it has "blown out" the testing equipment to where it wouldn't zero and vehicles testing next to me also failed for some strange reason.

 

[n8in8or]

While we are kicking-around thoughts . . .

From a theoretical standpoint, changing the pop should also come with an adjustmen in the tune. The way I see it is that by changing injectors with different pop points (and nothing else), the ones with the higher pressure will flow later in the rotation cycle. So the timing probably needs adjustment to match the pop pressure.

From a practicality standpoint, am fairly (to highly) confident that 6.5 tuners do not make any changes based on the injector's pop though. I did have one tuner concede that theoretically the timing should change, but nobody ever tested for this.

Timing! Thank you for bringing this up, I totally forgot that part of my experiment. I too was interested on the effects of pop pressure on timing. Like you, I believed that increasing pop pressure would retard the timing of the engine by delaying the pop event. So I measured my timing after the injector change with my Ferret adapter and a timing light........no apparent change to timing! I'm not 100% positive, but I believe that a pulse-type diesel timing tool would detect event changes at the injector even though it's being measured on the fuel line due to the non-compressible nature of fluids. I think this shows that the Injection Pump raises fuel pressure so quickly, that you can't see a change to the injection timing event - even if you change the trigger for the event by 700psi. Maybe it would affect the timing at a really high rpm, but not any rpm that our 6.5s will ever reach (well, not for long anyway [KABOOM!!]).

What this doesn't show is if what I'll call the "dynamic timing" was affected any. My results show that the pop pressure affects the burn of the fuel in certain conditions because of how my cold starts are affected. This would point to a finer or courser fuel atomization in my mind. Because of this, I could see a courser fuel atomization affecting timing because it would take longer for the fuel to light off. This only seems to be a problem for me at cold ambient temps with cold precups. Once the precups have some heat in them, my engine runs normally.

Interesting stuff for sure. I wish I had more time and tools to test these theories more thoroughly.

 

[Long Brown Train]

Boyle's law

The ideal GAS law does not apply to an injection pump (moving LIQUID). Careful you do not let that trip up your thinking.

 

[Big T]

I really like the idea of 350 hp and 600 lbs of torque.

 

[WarWagon]

I have advanced the timing more than initial startup shown here. To be clear the pumps are supposed to be "line to line" and that is timing cover line to pump line. See how far to the driver side mine is? No specs were supposedly ever published by GM otherwise. I recall high altitude adjustments were published...

 

[JayTheCPA]

Only reason I mentioned that timing adjustments were theoretical (at least for the DS4) was that none of the tuners cared what the pop was or made any adjustment for it.

From what I can tell (and maybe I am wrong) but it does look like the DS4 timing does advance as RPM's increase. At least that it is what it looks like to me when I monitor via AutoEngenuity. So perhaps that is why the few tuners I talked with did not adjust the timing . . .

 

[ak diesel driver]

So my ? is since the pump has been tweaked did it lose some of it's advance capabilities and hence the need for more advance?

 

[WarWagon]

So my ? is since the pump has been tweaked did it lose some of it's advance capabilities and hence the need for more advance?

Non-tweaked pumps that went before this one required the same advance. In fact this is near (But retarded as I was replacing chain) where the injector lines took a set. This is the reason I pulled the front of the engine off for the gear set: make sure it wasn't a stretched chain, jumped tooth, shearing key...

The current pump due to the smoke puff limiter looses the cold advance. In Phoenix Arizona, where it is on for less than 1 city block, it shouldn't matter.

 

[jrsavoie]

Does anybody have a link to Will's original pop pressure threads?

 

[n8in8or]

So my ? is since the pump has been tweaked did it lose some of it's advance capabilities and hence the need for more advance?

My pump still has mechanical advance. I can rev it with the timing light hooked up and watch the timing change.