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Thread: Above 5400 RPM... what actually happens? Can anyone check the codes?

  1. #1
    turbo addict
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    Above 5400 RPM... what actually happens? Can anyone check the codes?

    I've been reading the "Going away present thread" again and again, this post in particular.

    http://www.turbo-mopar.com/forums/sh...=1#post1117317

    If I understand it correctly, 87 TII calibration will no longer do fuel and spark calculation at 5400rpm. So any RPM beyond 5400rpm is just keep using the fuel/spark value at 5400rpm?


    Since I've gone to Microsquirt with a 24Mhz processor (LM runs at 1Mhz), I wonder if my engine will be able to make more power beyond 5500rpm given the same hardware.
    http://www.turbo-mopar.com/forums/sh...of-megasquirt

  2. #2
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Above 5400 RPM... what actually happens? Can anyone check the codes?

    Reeves uses stock electronics. If there's more power to be had, then I'm impressed.

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    Supporting Member Turbo Mopar Contributor
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    Re: Above 5400 RPM... what actually happens? Can anyone check the codes?

    i would like to be able to confirm this also. it's always been mentioned but i've never seen it proven up. maybe there might be a way to scan the correct locations to show what happens. it seems also that it wouldn't be THAT hard to eliminate some unnecessary code to make the routines faster. perhaps it's as simple as a 120/rpm = .022 (max loop time) = 5454 rpm. if that's the case MAYBE the calc could be done twice per loop...........
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    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
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    Re: Above 5400 RPM... what actually happens? Can anyone check the codes?

    What's not being said is just how Simple a system needs to be.

    Air pump + fuel = power

    Even if the LM was doing Nothing, you still have a rising rate FPR adding +1psi fuel pressure to the system above 5400rpm.

    Also, I never took it as it's doing nothing, but just that it's not altering anything outside of the already programed schedule for about 5400rpm

    So if your tune is Nuts on, you have nothing to worry about

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    Garrett booster
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    Re: Above 5400 RPM... what actually happens? Can anyone check the codes?

    I don't know how the code actually works so this is speculation. Based on what I read in that thread I get the impression that it stops doing certain calculations at that point in order to free up CPU time. It has to do this to some degree since the sparks are happening faster and faster as the engine revs up. If it just capped out at a certain speed then the advance and fuel injector timing would be further and further off the higher the engine revs. The fuel injection timing is less critical because you don't actually have to inject fuel at the time the intake valve opens. The spark timing is more important so I imagine it has priority. When I had an SMEC I noticed that the power loss light would react slower sometimes than others. By that, I mean it would be triggered quickly sometimes and other times it might take a second or two before it was lit under the same circumstances. There was another time when the speed limiter failed to work and allowed the engine to redline without cutting out until I slowed down to it's normal triggering speed. The speed wasn't climbing very fast either. To me that says that the CPU is being "overloaded" and has some kind of task scheduling in place that allows it to jump around and skip certain parts of the code until the next loop or possibly several loops down the line if necessary. I doubt it just stays at the same numbers when this happens. It's more likely that it just takes the last value and interpolates based on RPM or something of that nature. Rather than doing the full calculations. Honestly it amazes me that they were able to do so much with such a slow CPU. The code is obviously very well planned out.

    I think your fueling will be more accurate at high RPM with megasquirt but that's not to say you can't get things right with an SMEC. Just that what you put into the tables on the megasquirt will be more accurately realized than what you put into the tables on an SMEC. Like I said that's just speculation so take it for what you will.

    Who' going to be the first one to overclock their SMEC/LM? I bet you could get 2MHz if the other chips can handle it.

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    Slugmobile & MeanMini Caretaker Turbo Mopar Contributor wheming's Avatar
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    Re: Above 5400 RPM... what actually happens? Can anyone check the codes?

    Subscribed since this peeked my interest, as well as the original thread.
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    Re: Above 5400 RPM... what actually happens? Can anyone check the codes?

    Quote Originally Posted by Shadow View Post
    Air pump + fuel = power

    You forgot, advance timing = even more power.

    LM/SMEC has a table to advance timing as RPM goes up, but if the RPM timing advance stops at 5400, not all the hp is being extracted, given the cylinder head/cam/turbo can provide the flow.

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    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
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    Re: Above 5400 RPM... what actually happens? Can anyone check the codes?

    Quote Originally Posted by tryingbe View Post
    You forgot, advance timing = even more power.

    LM/SMEC has a table to advance timing as RPM goes up, but if the RPM timing advance stops at 5400, not all the hp is being extracted, given the cylinder head/cam/turbo can provide the flow.
    Like I said, I highly doubt the timing tables stop at 5400rpm. I think the adaptives may come to a screeching halt, but that's marginal loss at best.

    Also want to mention;

    You guys keep bringing SMEC into the equation. The One thing I did get out of that thread is that the SMEC platform that we chose to go with 20 years ago is the one that has the Most headroom and suffers the Least!

    I can tell you from personal experience, there is nothing strange going on with the SMEC electronics, not at 7500rpm!

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  9. #9
    Boost, it's what's for dinner... Turbo Mopar Staff Aries_Turbo's Avatar
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    Re: Above 5400 RPM... what actually happens? Can anyone check the codes?

    according to ken, from a proper engineering design perspective, above a certain rpm it doesnt have time to "properly" complete all the calculations for fuel and spark. as he said he spun the distributor with a variable speed makita grinder and had the factory diagnostic stuff hooked up to the ecu so he could test to see if calculations were being completed and they were not.

    ive also heard many times over the years that disabling the diagnostic routines above 4000rpms can help with this.

    that said, do they still work at higher rpms? sure, as many have shown..... but is it doing things properly from an ecu design standpoint? probably not.

    it probably helps that pumping efficiency drops as rpms raise so the last fueling calc is adequate for past 5400 rpm but the timing leveling out is not helping power.

    Brian
    Last edited by Aries_Turbo; 09-17-2017 at 09:52 AM.

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  10. #10
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
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    Re: Above 5400 RPM... what actually happens? Can anyone check the codes?

    Quote Originally Posted by Aries_Turbo View Post
    according to ken, from a proper engineering design perspective, above a certain rpm it doesnt have time to "properly" complete all the calculations for fuel and spark. as he said he spun the distributor with a variable speed makita grinder and had the factory diagnostic stuff hooked up to the ecu so he could test to see if calculations were being completed and they were not.

    ive also heard many times over the years that disabling the diagnostic routines above 4000rpms can help with this.

    that said, do they still work at higher rpms? sure, as many have shown..... but is it doing things properly from an ecu design standpoint? probably not.

    it probably helps that pumping efficiency drops as rpms raise so the last fueling calc is adequate for past 5400 rpm but the timing leveling out is not helping power.

    Brian
    Fair enough, and I can't say much on the LM because I never ran that platform for any amount of time or power.

    I can say that I have used the DRBII to monitor knock and TT along with every other parameter available and right to redline it has always shown the SMEC doing Exactly what it is calibrated for..........

    Robert Mclellan
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  11. #11
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    Re: Above 5400 RPM... what actually happens? Can anyone check the codes?

    since the smec/sbec is twice as fast as the LM i'm not surprised it works properly at the higher RPMs
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  12. #12
    turbo addict
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    Re: Above 5400 RPM... what actually happens? Can anyone check the codes?

    LM loop time, 22ms
    SMEC loop time, 11ms

    http://www.thedodgegarage.com/turbo_pfi.html

    MS1 loop time, ~.66ms
    MS2 loop time, ~.33ms

    http://www.megamanual.com/v22manual/mfuel.htm
    Last edited by tryingbe; 09-18-2017 at 01:03 PM.

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    Visit www.boostbutton.com... Turbo Mopar Contributor ShelGame's Avatar
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    Re: Above 5400 RPM... what actually happens? Can anyone check the codes?

    It doesn't stop calculating above 5400rpm. But, it will 'miss' the re-calculation of the spark/fuel (and boost for that matter - basically all control calculations) at high RPM due to the engine cycle time being smaller than the loop time - the injectors and/or coil fire before the 'new' fuel PW or spark timing can be calculated.

    In this case, the fuel and spark values would be carried over from the previous cycle's calculation. It simply means that a small adjustment that maybe should have been made, is missed. When the main loop starts again after firing the injectors/coil, the spark/fuel calculations would be again updated.

    So, it's definitely an accuracy error. But not necessarily a huge one. It's not likely that your timing or fuel demands change by a large amount from 1 cycle to the next. And, the worst case is your calculations are 1 cycle behind, every other cycle.

    On a stock engine at stock boost, this is never really a problem. But, a high speed, high power engine obviously this can cause some issues.
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  14. #14
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
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    Re: Above 5400 RPM... what actually happens? Can anyone check the codes?

    Quote Originally Posted by ShelGame View Post
    It doesn't stop calculating above 5400rpm. But, it will 'miss' the re-calculation of the spark/fuel (and boost for that matter - basically all control calculations) at high RPM due to the engine cycle time being smaller than the loop time - the injectors and/or coil fire before the 'new' fuel PW or spark timing can be calculated.

    In this case, the fuel and spark values would be carried over from the previous cycle's calculation. It simply means that a small adjustment that maybe should have been made, is missed. When the main loop starts again after firing the injectors/coil, the spark/fuel calculations would be again updated.

    So, it's definitely an accuracy error. But not necessarily a huge one. It's not likely that your timing or fuel demands change by a large amount from 1 cycle to the next. And, the worst case is your calculations are 1 cycle behind, every other cycle.

    On a stock engine at stock boost, this is never really a problem. But, a high speed, high power engine obviously this can cause some issues.
    Now that makes some Sense! Nice post!

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