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Thread: SA tables

  1. #16
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    That's my belief Dave, following that post's info but ramp to max timing at 100kpa and then flat line to redline, not ramp back down.

  2. #17
    Super Moderator dave w's Avatar
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    Quote Originally Posted by lionelhutz View Post
    That's my belief Dave, following that post's info but ramp to max timing at 100kpa and then flat line to redline, not ramp back down.
    Cylinder combustion chamber design and material (iron vs. aluminum) is an important factor to determine when to IGNITE the fuel air mixture. So the question is, what is the true meaning of "Fast Burn"? Piston dish or dome design is an important factor to determine when to IGNITE the fuel air mixture. Compression ratio is an important factor to determine when to IGNITE the fuel air mixture. Fuel Octane rating is an important factor when to IGNITE the fuel air mixture. The actual Air : Fuel Ratio is an factor to determine when to IGNITE the fuel air mixture. Emissions like Nox, CO, HC, and CO2 are factors to when to IGNITE the fuel mixture.

    To optimize when to IGNITE the fuel mixture requires more than basic engine information (camshaft profile, cylinder head design, compression ratio, vehicle weight, rear end gear ratio, ect) commonly reported to a "Tuner" Some "Tuners" over simplify the requirements needed for a "TUNE" vs. "PROFIT".

    A "BUTT DYNO" is not accurate enough to Optimize a timing table!

    dave w

  3. #18
    Fuel Injected! 84Elky's Avatar
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    Quote Originally Posted by lionelhutz View Post
    Interesting post, but I don't understand why at full throttle (100kpa cells) you would ramp to max advance, for example 28* for Vortec or 36* for conventional at around 3000rpm, and then start ramping the timing back down again. The example of dropping to 24* @ 4800rpm Seems like a good way to kill upper rpm power. Good way to stop knock though.
    Admittedly, I'm not a timing expert. And the amount of timing reduction in the example may not work for everyone. Maybe it should not be reduced at all. It depends on many factors because every engine is different. But two things cannot be disputed:
    1) Any timing advance past MBT (Maximum Brake Torque) reduces power, regardless of the octane of fuel used.
    2) Advancing the timing past what's needed will only increase cylinder pressure at TDC, and what is all that extra cylinder pressure doing at TDC -- it's trying to push the crankshaft out of the bottom of the engine.

    Below are some excerpts supporting the above from my notes. Attributions are not available except where links are provided.

    Engine Ignition Timing - Basics & Overview (Daytona Sensors)
    http://www.daytona-sensors.com/engin...uidelines.html

    The most significant factor to determine ignition timing will be the combustion chamber/cylinder head and piston design, this can vary significantly on different setups.

    So when you're tuning ignition and isn't limited by knock, you'll keep adding timing until the power stops increasing. If you keep adding timing it will eventually start decreasing due to the combustion working against the piston moving upwards.

    The best way to set ignition timing is on a load type dynamometer is to slowly advance the timing until peak torque output is reached.

    We can apply this prairie-fire analogy to the combustion space. At WOT, the air and fuel are tightly packed and burn quickly, so we don't need as much timing. At 2,800 rpm at WOT, 32 to 34 degrees of timing could be just about perfect for a typical pump-gas street engine. However, at very light throttle (14 to 16 inches of manifold vacuum), the air and fuel are far less densely packed in the cylinder. To make the most power possible at part throttle, we need to start the combustion process much sooner—perhaps as much as 40 to 44 degrees BTDC, depending on the engine's individual demands.

    On a dyno you can easily find where MBT is by using the method described in the above example, on the street it may be harder to tell, typical dyno loading allows for an engine to hit MBT where that's not possible on the street with actual loading as it will almost always result in pinging thus detonation before getting there. Its not uncommon for most dyno tuners to remove a global 3 degrees of timing or the like when removing a vehicle from a dyno to prevent detonation on the street.

  4. #19
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    Yes, it's all good stuff. But, I still haven't seen anything that says to run to a peak timing value and then ramp it back down as the rpm further increase.

  5. #20
    Fuel Injected! 84Elky's Avatar
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    Quote Originally Posted by lionelhutz View Post
    Yes, it's all good stuff. But, I still haven't seen anything that says to run to a peak timing value and then ramp it back down as the rpm further increase.
    OK, which is what I was trying to say: And the amount of timing reduction in the example may not work for everyone. Maybe it should not be reduced at all.

  6. #21
    Super Moderator dave w's Avatar
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    The attached .xls files are copy / paste Corvette timing tables (main & extended) from .bin files posted here at gearhead-efi.com

    The compare screen shots show surprising results. 95 Corvette vs. 96 Corvette --- Open File was 95 Corvette using Compare File 96 Corvette. Unknow B-Body vs. 96 Corvette --- Open File was Unknown B-Body using Compare File 96 Corvette. I used TunerPro for ODB1 files and TunerCats for OBD2 files.

    dave w
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  7. #22
    Fuel Injected! 84Elky's Avatar
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    One last note on this. Will agree with lionelhutz there does not appear to be anything (at least written) to indicate ramping down timing after all-in RPM. But if you look at the $8d spark tables below, which is what I was basing my discussion on, it's clear GM thought spark reduction was necessary. Who knows why. Hard to believe it was for emissions at WOT. Granted spark was increased slightly, but well after after all-in. I also find it interesting that the WOT spark is not all that aggressive (< 24 deg).

    It would really be interesting if someone who has dyno'd their rig could chime in on this. Don't believe a ZR-1/LT5 would be a fair comparison but who knows.
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  8. #23
    Super Moderator dave w's Avatar
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    Dyno performance Vortec TBI .bin attached. Engine specifications Not Available.

    dave w
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  9. #24
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    Quote Originally Posted by 84Elky View Post
    One last note on this. Will agree with lionelhutz there does not appear to be anything (at least written) to indicate ramping down timing after all-in RPM. But if you look at the $8d spark tables below, which is what I was basing my discussion on, it's clear GM thought spark reduction was necessary. Who knows why. Hard to believe it was for emissions at WOT. Granted spark was increased slightly, but well after after all-in. I also find it interesting that the WOT spark is not all that aggressive (< 24 deg).

    It would really be interesting if someone who has dyno'd their rig could chime in on this. Don't believe a ZR-1/LT5 would be a fair comparison but who knows.
    TPI spark advance is retarded where the TPI runners work the best at boosting VE. Cylinder pressure is highest there.

  10. #25
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    84Elky, I see the small reductions but it's not a ramp down just a bit of fluctuation and then the timing comes back. I too would expect that it's a bit of VE variation causing it.

  11. #26
    LT1 specialist steveo's Avatar
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    i wouldn't reduce timing at all past your torque peak unless it's compensating for a strange AFR in that region. the only factory calibrations i've seen that do that are ones designed to reduce power in the upper RPM ranges for de-rating.

  12. #27
    Fuel Injected! 84Elky's Avatar
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    Quote Originally Posted by dave w View Post
    Dyno performance Vortec TBI .bin attached. Engine specifications Not Available.

    dave w
    Interesting. If I'm looking at this BIN correctly with a $0D XDF, Spark is all-in at 4400-4800 with max of 27.4 deg, then after 4800 it drops to 26.0 deg up to 6000. Would be interesting to know if the dyno tuner did this because it provided max torque/HP, or . . . .? Wonder if the engine was maxed out at 4800 and he just plugged something in?

    Again, I'm not supporting decreasing spark after all-in RPM. It's just how I developed my curve. The important things are an all-in advance at some RPM, then increasing advance as MAP decreases.
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  13. #28
    Super Moderator dave w's Avatar
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    I see some similarities between the T.Wong $OD Performance SA table and $8D AUJP SA Table.

    dave w
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  14. #29
    Fuel Injected! PlayingWithTBI's Avatar
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    FWIW - I just tried @84Elky's Spreadsheet (set to 32* @ 3200RPM) on my TBI with aluminum heads and a fairly mild Lunati Voodoo cam (208/213). It seems to pull better throughout but, I do have some KRs at higher MAPs and RPMs up around 5200.
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  15. #30
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    Quote Originally Posted by steveo View Post
    i wouldn't reduce timing at all past your torque peak unless it's compensating for a strange AFR in that region. the only factory calibrations i've seen that do that are ones designed to reduce power in the upper RPM ranges for de-rating.
    Honestly this is not something you can do without a load bearing dyno or road tuning. In an octane limited environment such as my 11:1 383 on pump gas it is entirely possible to have the timing advanced in the 2,000-3,500 rpm range and retarded at higher rpm because the gearing/transmission does not allow the engine to see that low of a RPM in anything but first gear. Generally and engine will need more spark advance in 1st gear than it will in 3rd or 4th. My 383 has slightly more timing under peak torque than it does above peak torque. At WOT the only time I am below about 3,500-4,000 rpm is in 1st gear. The only time it is below 2,800 rpm at WOT is while the converter is flashing. Generally you can add more timing under the stall speed to help the engine accelerate and flash the converter.

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