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Thread: % difference between the low and high octane spark tables??

  1. #11
    Lifetime Member swingtan's Avatar
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    I think what Sid447 is saying, is that the KR settings still work as intended, even if the two spark maps are the same, (or for that matter, if the low table was set higher than the high table). The amount of KR is still controlled by the settings in the KR tables in the tune.

    However, what doesn't occur in the HSV GTS tune, or any tune where the low table is two close to the high table, is the "learning" ability of the Octane Scaler. This "preempts" the Knock sensor system, which is only a "reactive" measure. It must detect the onset of knock before it can react and pull timing, protecting the motor. Once consistent knock is detected, then the octane scalar moves the commanded timing down from the high table, toward the low table. This reduces overall spark advance and protects the motor from damaging pre-detonation.

    That's how it works in the factory setup, but once you start modifying the tune and optimising, you need to decide how you want to manage knock. For most professional tuners, a moderate amount of protection will be wanted. This is because you can't control what fuel is used in the car and how the car is going to be treated. So running 8' to 10' between the high and low table, and ensuring the octane scalar is working well, is a good option. For people tuning their own cars and are pedantic about using top quality fuel, who have massaged the spark tables with attention to IAT corrections, you can get away with much less.

    In any case, the high spark table (including the IAT corrections) should be set up so there is no detected knock under ideal conditions. If you can guarantee that there will be no knock, you don't need to worry about the difference in the tables. However, to be "sane", you'd have the 8' to 10' difference just to be safe. You nebver know when you're going to get a load of bad fuel, or have some other problem.

    Personally, I run 8' difference everywhere except around the idle cells, where I run 4' difference. I holiday in an area where 98RON fuel is not available and I tow a heavy trailer. So I make sure I have some "preemptive protection" built in to the tune. Apart from when I'm running the 95RON fuel, my octane scalar never comes off the high spark table though.

    Simon.

  2. #12
    Senior Member Sid447's Avatar
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    It's also a good idea,

    To check the tables B6219 and 6223: 6219 especially as some tune files aren't set to default to 1.0 which would mean the car may not start working off the HOT or H/LOT.
    B6223 is set to 2.0 in most GM files which seems reasonable enough.

  3. #13
    Lifetime Member smslyguy's Avatar
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    Quote Originally Posted by Blacky View Post
    Its been while since I had my GTS. They were calibrated as speed density tunes from the factory and I'm pretty sure like Joe said they defaulted to the low spark map. That would explain why the HSV calibrators felt the need to pull the low spark map up to match the high spark map.

    Shameless plug... EFILive's speed density custom OS for the LS1 restores the full high/low spark mapping for SD tunes for the LS1.

    Regards
    Paul
    So if I am running c.l.s.d. on my American car would it pay to reduce my low spark table?
    2001 camaro z28 ss vert with factory slp upgrades, Hooker long tubes, 3"y-pipe to a 4" muffler, ,airlid,s.s.r.a. ,t.c.bypass,descreened m.a.f. 232/234 .595,.598 +2 comp cam with ported and polished stock heads with .650 lift dual springs and a bowl grind. tuned with EFI Live. All combined to achieve 29 m.p.g. and 399 r.w.h.p. with 384 lbs of torque. sold...

    Now own a 2015 1LE camaro

  4. #14
    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by smslyguy View Post
    So if I am running c.l.s.d. on my American car would it pay to reduce my low spark table?
    Have a look at the HI and LO spark tables in a stock Fcar tune.

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