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Thread: E39 GMH 3.0 SIDI: 91 vs 98 Octane

  1. #1

    Default E39 GMH 3.0 SIDI: 91 vs 98 Octane

    Just to separate this from the PID thread.....

    I got down to 70KM to empty and figured it was as good a time as any to compare 91 and 98 octane fuel. The car had 460km on the clock, so is still very, very new. The comparison is still valid though.

    • Holden VE SII Sportwagon (Omega)
    • 3.0L SIDI engine
    • 6 speed auto
    • E39 ECM
    • T43 TCM

    • Ambient Temp: 32'
    • Rel. Humidity: 29%
    • Barometric Press. : 97kPa
    • 2 Adults and 2 teenagers on board.

    Here's the log details, Note #1 is on 91, the "Chart Inspector" is in the middle of the tank refill and Note #2 is on 98.

    Octane 91 98
    RPM 2298 2350
    ETCTP 52% 58%
    APP 37% 40%
    Spark Adv. 10' 15.5'
    KR 2.5% (3' peak) 0'
    MAP 95kPa 96kPa
    VSS 56kmh 57kmh
    MAF Air 57.95gm/S 54.78gm/S
    IAT 37'C 47'C
    Engine Trq. 235.0nM 237.5nM

    So.... I think the difference is pretty obvious. Some of the really interesting points here....
    • Spark advance came up 5.5' with similar engine load and RPM.
    • MAF air speed was slightly reduced.
    • Calculated engine torque rose slightly.
    • No KR with 98 fuel.
    • The ECM applied significant throttle torque reduction when shifting with 98RON fuel.
    • All this occurred with an additional 10' of IAT.

    The car also felt much better on the road, an indication that it's suffering badly from the lower octane fuel. I think Holden should have made this a 95RON minimum engine, really it's not happy with 91. Note also that the fuel trims also reduced, indicating it was running slightly richer on the 98, so maybe the use of 98 would get better value for money....... It's an interesting thought.

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    Last edited by swingtan; February 4th, 2012 at 11:21 PM.

  2. #2
    Senior Member Dieselman's Avatar
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    Apr 2010


    What Comp Ratio is this engine Simon??

    They might like E85 even better??

    Interesting results
    Last edited by Dieselman; February 4th, 2012 at 11:09 PM. Reason: Typo

  3. #3
    Lifetime Member GMPX's Avatar
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    Apr 2003


    Engine comp is 11.7:1.
    I think Holden tried to put too much timing in them for low grade fuel, the US cals on the same engine (eg, Cadillac SRX) took a different approach, less timing but very different cam adjustment maps, yet they make the same power and torque. It would be very interesting to see how an SRX runs on low grade fuel as far as knock goes.
    Swingtan, if you can locate somewhere that has E85 I would recommend giving it a tank of that too. Running these cars on 98 Octane kind of defeats the intended reason you would buy one. You accept that running a supercharged LSx engine on 98 is mandatory, not for a grocery getter. Ideally, we need to come up with a nice tune for E85 that isn't a killer on fuel economy. It should be possible, I think it was GM that directly claimed the 2012 Buick Regal was able to get the same fuel economy on E85.
    I no longer monitor the forum, please either post your question or create a support ticket.

  4. #4


    Good point! I can get E85 from the Caltex on FTG road, so may need to try that at some stage. The car has "E85 compatible" all over it so I think Holden really want you to start using it. Unfortunately, the fuel card is Shell only and they won't even do E10 anymore and I doubt they'll ever do E85. I should be able to get the odd tank full from other servo's though and claim the expense back.

  5. #5
    Senior Member
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    Nov 2007


    Here are some charts for comparison, I've set them up the same as Simons ones for easy viewing. These are from a 2011 Holden Captiva with 3.0L SIDI on NZ 91octane fuel

    Similar conditions to Simons chart
    Click image for larger version. 

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    Cruise control set at 100km/hr going from flat to incline. Check out the KR
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  6. #6
    Lifetime Member GMPX's Avatar
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    Apr 2003


    I recently did a couple of logs on mine for the benefit of Simon to show what they are like on E85 fuel. The actual ethanol percentage was showing 53% as it was an eFlex fill on a 1/4 tank of 91. Anyway, on the stock tune the most knock recorded on a one hour drive was 1.1 deg and this happened just once, well below the typical 3 to 7 degrees these things seem to constantly hit on just 91 Octane. I usually give the OEM's the benefit of doubt on why they do things with the cals, but I can't imagine why they would want to be running at 4+ degrees constant knock retard as these Holden's tend to on 91. They did it on the first release of this engine in 2010, and looking at Simon's logs of a brand new 2012 model nothing has changed! It would be really interesting to see a log from a US 3.0L running their 87 Octane to see if they are on the ragged edge too on low grade fuel.

    Click image for larger version. 

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    I just noticed something really cool too. Look at the VE number in the log above, that is the value calculated by the Virtual VE tables, if you ever wanted to question how accurate our calculations are, check out the VVE table below from the 3.0L SIDI with the correct amount of cam timings applied to match the log, it's so close it's scary, 1201 on the log vs 1197 calculated.

    Click image for larger version. 

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    Last edited by GMPX; March 18th, 2012 at 09:34 PM.
    I no longer monitor the forum, please either post your question or create a support ticket.

  7. #7


    FWIW, I hit a new record a couple of days ago. -1.5' total timing advance........ This engine is crying out for some work and will get to it shortly. Fair enough it's running 91 and 11.7:1 compression, but I think the PE mode timer may be hurting things here. It's going to take some lateral thinking.

  8. #8


    Update Time:

    Over the past week I've been working on what I feel are the two major issues with this vehicle...

    1. The amount of KR the stock tune exhibits on 91 RON fuel.
    2. The sluggish / non responsive feel of the car in general.

    Let's start with the KR.
    If you look at the tune, you'd think the High Octane spark table was set for E85, it's really high, too high. But the tune also runs very aggressive Octane Scalar Decrement settings, so it learns down quickly to the low table. The only problem is the low table is quite high as well, so it still knocks. This is complicated by the shape of the tables not being great, so KR at cruise speeds ( where the timing is quite high ) cause a drop in spark timing in the power cells where it may not normally have any KR. So step one was to drop timing across the board on the high table and to blend some of the peaks out and level the table a bit. Then I copied the high table over the low table and removed 8' across the board. This obviously reduced the occurrences of KR, keeping the spark closer to the high table, so keeping the average spark timing higher every where.

    Further more, I spent a fair amount of time reading up on VCT and the effects of cam timing when the inlat and exhaust cams are adjusted individually. I won't go into the full details, but the basics are that the high cam advancing used in the stock tune basically results in...
    1. When the exhaust cam is advanced, it bleeds off cylinder pressure early, reducing the "drive" toward the end of the power stroke and allowing more exhaust gas to excape out the exhaust.
    2. When the inlet cam is advanced (significantly), it allows exhaust gas to enter the intake and dilute the intake charge. This reduces over all power, but acts as mechanical EGR system, reducing emissions.

    So what I've also done is to reduce the maximum advance of both cams by up to half, attempting to make more use of each power stock and reduce the intake charge dilution. My thinking is that intake advance has been used for emissions, but then exhaust cam advance is being used to reduce the amount of EGR. The combined advance should have helped with reducing pumping losses as light throttle, but I'm not convinced it was working as designed. So I've gone for less advance overall.

    Finally, I've altered PE mode settings to bring it in earlier and allow the get the fuel it needs to make some power. While entering PE mode earlier will use more fuel, reducing KR and keeping a higher average spark timing "should" give better overall efficiency. At least that's my theory.

    I'm now seeing the odd KR spike to 3' with rare hits at 4.5'.

    Next up, the sluggishness.

    Reducing the KR in the tune helped a bit but there were two main areas that have been used so far to pick up the driveability of the car.
    1. {B8802} Torque Model: This table basically tells the ECM how much theoretical power should be delivered depending on the engine RPM and the commanded TPS. The ECM will then open the throttle a calculated amount to provided the desired torque. These cars feel really dead off the line, mainly due to this table commanding little power at low RPM and the pedal flat to the floor. So the the easy fix here is to increase the desired power where you want more power. A word of caution though, increasing it too much in the lower cells will result in a car that will drive it's self easily up to the local speed limit...
    2. Gearbox Tune: I spent a fair amount of time working on the previous generation V6 where I could only tune the auto. This taught me that a good gear box tune can cover a myriad of problems in the engine tune. I think that in this case, the stock tune is trying to rely too heavily on keeping the revs low and locking the TCC too long. While this keeps the car in a higher gear, it also loads the engine more, causing KR and driving it in to PE mode more often. Every one should know that laboring an engine will never allow for peak efficiency, so I see no reason to do it.
      I've altered the speed settings for part throttle shifts and TCC controls so that,
      • the TCC releases sooner as engine load increases. This allows the TC to do its job of torque multiplication, and allows the engine to pick up a few Revs.
      • the gear box will down shift sooner, picking up more RPM and reducing engine load by dropping gears.

    I've also firmed up the shifts to make the car feel better through the gears.

    Prior to to tuning, I had an economy figure of 12.3L/100km (19.12MPG) averaged over 4,500Km (2,800m) and mainly suburbs driving in peak hour traffic. Since the adjustments, economy is now at 11.4L/100KM (20.6MPG) but it's only been over 450KM (280m), so it'll probably come up a little. However, the car feels much better to drive now and while it's no where near the same as the other car, it's very enjoyable to drive.

    More to come as more is found.....


  9. #9
    Joe (Moderator) joecar's Avatar
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    Apr 2003


    Simon, thanks for the update, very interesting info there.

  10. #10
    Lifetime Member GMPX's Avatar
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    Apr 2003


    Funny, I was Emailing Simon over the weekend about these engines and how he was going tuning he's as our car also has one. My conclusion is that it was never designed to run happily on Australian 91 Octane in a car with the weight of a Commodore, I would hate to think what one of these would be like towing a boat on a 35°C day. One thing with the E39 though, when you floor it off the line and you only see 40% at the blade, also check the MAP reading, if it's 100kPa (or close enough) then the ECM will not open the blade further than it needs to be. This makes perfect sense, it would be quieter through the intake, faster to react for traction control or power reduction. I know it looks bad on the logs and had me going for a while, but if the engine is at 100kPa then there is no reason the blade needs to open up further.

    One thing I've found, people I've spoken to complain the engine feels harsh at 2,500 - 3,500 RPM at full load. I've found the exhaust cam table to be the problem, for some reason Holden put a big spike at this point, with the spike removed the engine feels much nicer.
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