The DISI-MZR fuel system (Warning: Science Heavy)

Discussion in 'Mazdaspeed 3/6 Fuel, NOS, Meth, & Water Injection' started by Enki, Feb 12, 2016.

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  1. Enki

    Enki Motorhead Platinum Member

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    Aiight, those of you that know me know the drill. No TLDRs for you this time; you can get scienced or you can get the fuck out.

    Starting out with some simple stuff most people will know:
    1. Stock HPFP (high pressure fuel pump) internals need replacing after a certain mod/power level.
    2. Stock injectors are good for about 400 WHP, provided you have upgraded HPFP internals to feed them.
    3. Stock ITFP (in tank fuel pump) is good for probably about the same 400 WHP; not sure anyone knows for sure but feel free to add if you do.

    ...And that's about it. That's what I'd wager most people know about the stock fuel system, primarily because until today, that's pretty much all I knew about it too. But now, at least, I have a better idea as to why these 3 (though really I'll only be going in depth on the first two) commonly held ideas ring true for us when they don't always for other platforms with similar technology (like the ST).

    Most of you are probably also familiar with what it looks like when fuel runs out; if you are or if you aren't, I'll inform you and/or refresh your memory with these two snippets of log (provided by another, not from me):

    dip 1.PNG


    dip 2.PNG

    The common thread between these two logs (and likely any other logs anyone wants to donate to this thread showing running out of fuel on stock HPFP internals), is that pressure falls off around 3800-4k RPM, peaks in badness around 4k-4500 and then comes back up thereafter, returning to normal shortly after 5k RPM.

    The most important question I can think of regarding these logs isn't how to fix this issue, since we already have a very easy grasp on that, but rather, why does pressure return? One might think that it's because the stock turbo can't flow enough air, and that is essentially correct; but if you look closely at both of the logs, airflow is increasing with RPM and yet fuel still comes back. In both logs, it's even enriching the AFRs as it does so....So what gives?

    Well, my epiphany came with a "well, duh" moment after I realized the math behind it. This came about because I wanted to figure out how much fuel an upgraded HPFP can actually supply (and the answer to that is ...amusing... to say the least).

    We (should) all know that injectors are tested at a linear rate and pressure; this is evident in how they are labeled; 1000 cc per minute, 75 pounds per hour, etc; it's simply x flow over y time. Well, this static flow/time scenario doesn't actually apply to the HPFP, specifically because it's what's known as a positive displacement pump.

    What is that? Well, I'll put it like this: Let's say you have a 5 gallon bucket of water, full to the brim, and want to remove water from it. Naturally, you step in it with one foot because fuck it, why not right? As you do so, the water that your foot and leg displaces flows out, and when you remove your foot from the bucket (hopefully without getting that shit stuck on your foot like a retard and splashing about), the water level drops. It's what makes hundreds of tons of huge ass boat float; they displace more than they weigh. Kind of like when you're in the pool trying to hold a basketball under the water and it comes back up and knocks your fucking nose back into your skull....But I digress.

    Where was I? Oh, right. Positive displacement pumps. You see, much like the car engine, the HPFP has a bore (the face of the HPFP internals) and a stroke (the lift provided by the camshaft lobes), and this gives it a measurable displacement. Because it's connected to the cam, it's easy to figure out how many cycles per second it does and how that relates to engine RPM, which is really important here for the following reason:

    While the injectors have the same flow potential (their flow rating) at idle and at 8,000 RPM (for example), the HPFP does not; the difference between idle flow and 8,000 RPM flow basically fucktuples (that's a scientific term, BTW).

    Make sense? No? Then I'll add some spreadsheets. Bitches love spreadsheets.

    EDIT: THIS CHART IS NOT ACCURATE!
    Stock.PNG

    I'll preface this by saying my lobe measurement is probably off by at least a little bit, and that it doesn't matter that much for reasons that will become clear soon (I promise). Also, this spreadsheet doesn't factor in things like spray window reduction from timing, pressure loss due to HPFP lobe placement, etc.

    You can see I've got the bore, stroke, camshaft lobes and the injector size populated (which is cut in half because it's not possible nor safe to run a DI injector at 100% true duty cycle like you can a PI injector, due to it injecting directly into the combustion chamber). These values all represent the stock HPFP internals which don't look like they are too much smaller than the Autotechs, but keep in mind the area of a circle grows drastically with just a small change in diameter; thus, the Autotechs have about 52% more bore area than stock, which is a substantial gain.

    Starting at the top, the first red box reads "Max Flow RPM;" this is the RPM I calculated that the injector would no longer be able to keep up with the HPFP flow wise; obviously, this doesn't quite add up with the logs posted earlier as pressure was still falling up to 4600 to 4800 RPM; there are any number of reasons for this including but not limited to there being no pressure generated by the HPFP during injection events, or possible float/hangs in the internals that cause it to not cycle properly. More on this at a later time, if you all want to discuss that; I have multiple pumps I can tear down and show the goods, so to speak.

    Moving on, the first black line separates the section for overall HPFP flow based on bore, stroke, and RPM (cycles per minute). The gray row has RPM, the purplish row has the flow data in CCs (note this is overall flow and not per injector flow).

    Below that, however, is injector flow information. The gray line is RPM as above, but the purple one is different. This is the overall HPFP flow output divided by the number of injectors (with appropriate considerations for cycles, RPM, injection events, etc). Below that, the green line shows HPFP flow (per injector) vs the listed injector flow number in yellow at the top. Negative numbers here mean that the injector is capable of flowing more fuel than the HPFP can supply, positive numbers mean the reverse. Notice anything yet? That's right, the number goes positive (even with stock HPFP internals) after 4,000 RPM. It is likely that my measurements are a tad off and this should actually go positive at/around 4500 according to the previous logs, but again, this doesn't take into account lots of variables.

    Probably the most amusing thing to note here is that even with stock HPFP internals, the math suggests that a car spinning 8,000 RPM would benefit from aftermarket injectors that are DOUBLE the stock flow rate. That would be roughly somewhere near 400 horsepower.

    You're probably asking yourself "So wait, this motherfucker is saying you don't need HPFP internals to go big turbo!?" Well, yes and no. Chances are, on pump gas and without a tune/turbo setup to properly match that kind of configuration, you're going to need a lot of JBWeld to fix the hole in your block from running out of fuel at low to mid RPMs. For my build, however (which is a destroke high RPM build, just look for "DISI-MZResponse" in the Genwon build diaries section), it *might* be *potentially* feasible to run stock HPFP internals for lower power tunes. It would be hilarious, at least, and I might even try it briefly if for no other reason than to satisfy my own curiosity once my motor is built.

    Back on topic. The nasty flow math gets better with Autotechs, obviously. I'll let you peruse this one on your own and compare to the stock one above:

    EDIT: THIS CHART IS NOT ACCURATE!
    Autotechs.PNG


    +50% flow at 4,000 RPM when stock internals were just breaking even; a listed full 2600 cc worth of injection room at 8,000 RPM. That is power waiting to happen.

    But wait, there's more to this than just flow rates and pressures. Timing is pretty important too, as is the type of fuel you run. I'll actually need people to chime in with their logged IDCs (injector duty cycles) to further contribute to this idea, but I'd wager that those running smaller mixes of E85 can get away with higher IDC numbers than people running full E85 before the engine starts to stutter or misfire; this has a lot to do with spray window, timing, and the chemical properties of the fuel. For example, I've heard of people running in excess of 130% IDC without issue, while my car wasn't able to go past 105% without misfiring.

    Some explanation for those that might not know:
    In a port injected car, the fuel generally sprays on top of the intake valve and will sit there until the valve opens and allows the fuel to enter the cylinder along with a bunch of air (under high IDC values, anyway; for emissions and economy, most modern cars will start to spray just as the valve(s) start to open).

    On a direct injected car, however, we can spray fuel during both the intake stroke (when air is drawn in through an open intake valve) and during the compression stroke (when all the valves are closed and the piston is on its way back up to top dead center for firing and the power stroke). Spraying fuel during the spark event can cause it not to fire at all or to fire weakly/misfire as the flame front is blown out (AKA spark blowout). This is also why DI injectors may have a huge listed rating, but can only operate at half that value.


    Anywho, let's see what the timing and fueling relationship looks like:
    IDC.PNG

    Here's what we've got going on here:
    1. RPM across the top in grey (first value can be changed so it's yellow in my sheet)
    2. MS Per Degree is how long it takes in milliseconds per degree of crankshaft rotation
    3. The listed DI injection spray Window, which is essentially 180 degrees of crank rotation in milliseconds (and why it gets smaller as RPM goes up; another drawback that port injection doesn't have)
    4. Ignition timing, which is always in degrees of crankshaft rotation
    5. Timing MS which is how much time in milliseconds the spark event takes off the spray window (because you don't want to spray fuel during/after the spark, that's bad, mmmkay?)
    6. The Effective DI Window which is the maximum injection spray window in milliseconds
    7. And finally the % Window Lost shows you how much spray window you lost to timing in a number that's more relate-able.

    What's interesting to note about this table is that the same timing values affect the fueling window by the same amount, regardless of RPM. This is because fueling window and timing are both based off the same core number: RPM and more specifically, MS Per Degree.

    Going back to how timing affects fueling, you can see that 14 degrees timing reduces the fueling window by 3.89%, while 22 degrees reduces it 6.1%. Why is this relevant? Well, most pump gas cars will run a maximum timing value at or around 14 degrees, while most corn mix cars will run max timing at or around 22 degrees; this all depends on their redline, however, and going further up in RPM winds up needing more and more timing to keep the power band flat. There is a reason for that, but I'm not really prepared to go into that at this time.

    SO, the difference in timing alone costs a car going from pump gas to a corn mix about 2.21% fueling headroom, assuming both cars only go up to 100% IDCs.

    And on that note, I'll end this thread and give everyone interested time to ask questions which I can do my best to answer and add to this post at a later time.
     
    Last edited: Oct 23, 2016
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  2. Sneaky_Built_Vega

    Sneaky_Built_Vega Greenie N00B Member

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    You're a gem, Enki. This is the kind of information that should be accessible to members of the forum who have donated. Either way, I'll try find some time to contribute some data soon.
     
  3. mps611

    mps611 Greenie Member

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    science bitch!!
    [doublepost=1455277982][/doublepost]science bitch!!
     
  4. JgamB

    JgamB Greenie Member

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    I like the premise, but would also like to see more logs corroborate the 4-4.5K RPM "deficit". http://revisionsrus.com/logs/128 might also be useful to you. This log has my car hitting 2.5 load at ~4.4K RPM, and it hasn't been corrected for the hidden open loop trims. You can see it lean out from 11.8 to 12.7 AFR and recoup 8% IDC, and basically stays there until I lift at 6.7K. Normally it would approach ~115% IDC in a bit warmer weather. I don't think going lean at mid-range RPM is a particularly good strategy, but I suspect that does open up the prospect of tuning someone without HPFP internals on a K04.
     
  5. PoonFlavoredTang

    PoonFlavoredTang Greenie Member

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    A stretched out pump gas with no aux tune. Stressing out the fueling system for you. I can throw it on the dyno as early as tomorrow if need be. I also attached the actual log.

    Also I hit some pretty decently high loads around the 4k area and seem to maintain hpfp pressure pretty well. I also have some logs here @Enki somewhere that I used stock internals on a GTX2867 lol. Don't ask. They were merely at spring pressure though which was 14psi I believe.

    [​IMG]
     

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  6. Enki

    Enki Motorhead Platinum Member

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    I mostly wanted to look at cars with stock HPFP internals to show this, since out flowing the injectors with Autotechs (or the like) is pretty easy.
    One thing I did on my car, was run a corn mix on stock HPFP internals and a tune; remove VVT, you drop airflow in the danger range and can make the same power on a lot less boost.
     
  7. PoonFlavoredTang

    PoonFlavoredTang Greenie Member

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    If someone wants to put together a gofundme for another engine build I"ll gladly swap in some stock internals on this tune.
     
  8. Enki

    Enki Motorhead Platinum Member

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    Yeah no. Lol. Maybe if you had a smaller spring (like 5 psi) and some patience you could test that.
     
  9. AYOUSTIN

    AYOUSTIN Greenie Member

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    I'm really digging all of the excel layouts and the theory with how well it is explained and presented!

    One thing to consider though, regarding the last part about the injection window. Though I don't have solid evidence of it, it's always been my belief that DI cars would fare better at high RPM than PI cars would (or at least DI wouldn't fare as bad as believed). PI is not window limited like we are but they are still limited by the intake valve open time which gets absurdly small at high RPM. At only 6000RPM our intake valve is only open for 0.005777 seconds. If you wanted to rev to say 10k then you're looking at a valve open time of 0.003466 seconds. With PI you have to be spraying A LOT of fuel to get enough into the combustion chamber. With DI less fuel can be sprayed for a similar power level since you still have ~180* to spray fuel even though yes it is still time limited but that is affected by things such as piston speed and rod angle.

    Which is another reason why I think lowering the rod/stroke ratio has some advantages. With a lower rod/stroke ratio you have more piston dwell time which would expand the injection window, increasing the ms/degree. The drawback is that you would have to run more ignition advance which would have an inverse effect on the ignition window. This is also true of your build with the higher rod/stroke ratio, where you'll be able to run less ignition advance but your ms/degree will drop due to the shortened dwell time. What I'm not sure of is which has a greater effect on the injection window, ms/degree or overall ignition timing.

    Having a very high fuel pressure also helps us considerably since it means that the fuel can be pushed into the chamber at a faster rate due to the large pressure differential towards the beginning of the window (essentially how higher fuel pressure helps any car). It's been my belief that there is a point of diminishing returns with fuel pressure when it comes to DI fuel pressure, hence why we don't see any significant gains in fueling headroom when using higher rated PRV. I do still think though that higher fuel pressure still has it's advantages because like I said before, it allows fuel to move into the combustion chamber faster due to a higher pressure differential and the higher the pressure differential the more total fuel will make it into the combustion chamber before the injector closes, but that's only prevalent to the beginning of the injection window, as the intake valve closes and the piston rises to create pressure that pressure differential will drop and fuel will flow in slower. The other advantage is atomization but this is something that I still have to look into as I'm sure there's also a point of diminishing returns with fuel pressure vs atomization.

    That's mostly just my thoughts, I don't really have any backing to it other that what I've learned in school and what I've learned reading papers online so don't take any of it as solid truth. I'm really interested to see where this thread goes.
     
  10. Enki

    Enki Motorhead Platinum Member

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    A couple things:

    1. PI cars (specifically boosted ones) can still cram shitloads of fuel into the cylinder with air to match, even at high RPMs. This has a lot to do with cam profiles. A PI car can just leave the injector open (@100 IDC, which isn't the greatest idea), but DI cars actually have to time it properly or it can hurt parts; spraying before the exhaust valves are fully closed can raise EGTs or even melt a catalyst if you're running it hard, for instance.

    2. Higher rod:stroke ratio actually increases piston dwell at TDC and reduces dwell @ BDC, with shorter r:s ratios being the opposite (which is why most vehicles run a r:s ratio in the 1.5-1.6 range, as most cars aren't meant for racing). This hurts VE/torque at low to mid RPMs since there's less time before the piston starts back up the cylinder (and thus reduced cylinder filling/VE).

    3. I'll be going as high compression as I possibly can on my build, which will also reduce required timing before MBT. Higher compression also increases thermal energy harnessed by the engine (efficiency), but requires lots of octane to work properly that way (because compressing anything makes it hotter and thus more prone to detonation in the case of air/fuel mixes).

    I'm actually expecting my MBT (with 2.2:1 r:s ratio and 13:1 compression) to be somewhere around 6-10 degrees @ 6k RPM or thereabouts on full E85. Both of these should expand my overall spray window considerably, and my HP per airflow (and thus MPG) should improve as well, since upping the compression ratio makes better use of the fuel from a thermal efficiency standpoint, and having a longer r:s ratio does the same for cylinder pressures with less overall timing (better torque at lower boost and airflow levels).
     
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  11. AYOUSTIN

    AYOUSTIN Greenie Member

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    I totally agree that injection timing is critical for DI, I was just saying that we might not be as constrained as originally thought.

    After thinking about it yes, TDC dwell time would be increased which would make the engine more knock prone but the rest is still true with there being more dwell time at BDC and allow for a longer injection window.

    I think that a high rod/stroke ratio with high compression are good compliments for each other and that you're going to get good results from it. The longer dwell time at TDC would allow less chance for abnormal combustion and make cycle to cycle combustion events more consistent which is very good. My gut tells me you should be able to run 10 degrees at 6k but we'll see when you start tuning. I'm still curious about the other end of the spectrum with lowering the rod ratio and what that might bring to the table for us. The biggest downside I see to it is increased wear due to the higher rod angles but that can be mitigated with an offset gudgeon pin. Another disadvantage would be that the engine would be a bit more knock prone.
     
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  12. Sneaky_Built_Vega

    Sneaky_Built_Vega Greenie N00B Member

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    So, among the customers I have tuned, I had one that thought his HPFP was upgraded from the previous owner. Without going into too much detail, he had his block built and installed the bolt-on GTX 3076 with other supporting mods (at this point it was assumed by him that HPFP internals were upgraded since it had full bolt-ons on stock block). I dialed in his closed loop remotely and then he came by for me to dial in the rest of the tune. On the first WOT pull I had my eye on everything, besides HPFP pressure. As I looked at the log post-pull, my jaw dropped. Please refer to the attached log for data. Both VVT and Timing Advance were still at my base map values, fuel pressure drops hard past approx 5200 RPM and around that same point AFR leans out. Needless to say, I had him drive it easy until he upgraded HPFP internals and then we got back on the tune afterwards.
    [doublepost=1455486038][/doublepost]
    So, hopefully the data I posted will help determine that the stock turbo definitely does not flow enough air at higher RPM to put a strain on stock HPFP internals since pressure does recover.
     

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    Last edited: Dec 31, 2017
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  13. Enki

    Enki Motorhead Platinum Member

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    Well, my math suggests there should be more than enough fuel with stock HPFP internals, so either it's wrong, or there's another factor that isn't taken into account and should be.

    Clearly, this warrants further investigation, but I'd like to know more about the car in question (year, etc) to further analyze the log (which is showing > 400 whp and 400 wtq using my vdyno settings).
     
  14. Sneaky_Built_Vega

    Sneaky_Built_Vega Greenie N00B Member

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    Here's a snap shot of the log for ease of viewing: HPFP drop.PNG
    [doublepost=1455487271][/doublepost]
    The car is an 07' Mazdaspeed 3 With the following power mods: xs power exhaust manifold, ported stock intake manifold, garrett gtx3076r w/tial ewg, jbr 3.5" intake, CP-E DP and straight pipe exhaust.
     
    Last edited: Feb 14, 2016
  15. Enki

    Enki Motorhead Platinum Member

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    I'm assuming the log was 4th gear, correct?
     
  16. Sneaky_Built_Vega

    Sneaky_Built_Vega Greenie N00B Member

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    Yes, that one was a 4th gear log.
     
  17. Enki

    Enki Motorhead Platinum Member

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    Still pretty impressive that it made that kind of power on stock HPFP internals.
     
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  18. dsb_chicago

    dsb_chicago Greenie N00B Member

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    good read! who doesn't love science!!!o_O
     
  19. Ryan Wolf

    Ryan Wolf Greenie N00B Member

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    this was a great read! learned a lot from it. thank you!
     
  20. simply_pandora

    simply_pandora MSO Chicks Greenie Member

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    Thank you for this. I had a local recently who had stock internals that were dying out. When he finally got an AP, we were able to log and see what the car was doing. When we met him, his internals were gummed up, pressure relief valve was shot. Hooked him up with another local who had a spare PRV, and gave him a set of stock internals that were in better condition than his originals. Eventually he got some Autotechs and has gotten a tune from Dale since then and the car is doing better. It's pretty cool to get more info as to why it was happening because we were watching the same thing... the fuel starvation in random cells with a lean spike that followed (naturally, due to the lack of fuel), and thought the same thing in regards to the flow of air vs amount of fuel vs hpfp pressure. Still have some of his datalogs, but I think you might have stock internal failure logging covered.
     
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