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Thread: looking for thoughts and tips on tuning SA tables

  1. #1
    Fuel Injected! 1leg's Avatar
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    looking for thoughts and tips on tuning SA tables

    I have learned a lot over the last few weeks and the Suburban is running really good. I have tuned the VE table to get the BLMs really close to 128 in most of the cells. my avg is somewhere around 125-133 in most cells. and the main cruse speed cells are a little tighter, 126-131. I'm really happy with the way the truck is running. I'm now wanting to start tuning the SA. I have heard a few theories like keep advancing tell you get knock then back off 2. Then i heard that advancing tends to lean a cell while retard tends to enrich a cell.
    Looking for advice, thoughts and tips on how to start tuning SA tables.

    1 question. With my old carbed drag cars we locked out the dist and advanced the timing and jetting until the car slowed down. Should i try and get the SA advanced as high as i can and tune the VE up to eliminate knock? I'm not drag racing the Suburban but want it to make more power and still run 87octane gas.
    1993 RCSB 1/2, 350/4l60 Eaton locker 3.42-1. Drag truck ET 10.84 1/8mile. Build Thread
    1989 V2500 Suburban 350/th400, 4.11 gears, Tow truck, needs TBI 454 swap. Build Thread

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    Spark advance and fuel delivery are closely related. Now that you've decided to make changes to spark there's a good chance you'll be going back over your fuel needs. Especially if you've been using lean cruise fuel mode.

    Work to reduce acceleration enrichment and use deceleration enleanment whenever needed. Aim to get these values and the VE tables so well adjusted that there's no INT or BLM correction right after the throttle is opened or closed. Tune PE enable values so they work when you need them, not when you want them, to prevent spending unnecessary time in power enrichment.

    The faster the heads can burn fuel the less advance is needed. With the drag cars the really sharp guys didn't advance timing until the car slowed down, they stopped advancing it when the car stopped responding. There's a point where you're past best power but you're not making knock. If you have an oil temp gauge you'll be able to see this point as where the engine runs fine but oil temp is hotter. All it takes is one degree too much spark to see this. It won't show up in coolant temp and it may not show up as a substantial increase in EGT, either.

    Don't believe that more timing is necessary in all situations. I have calibrations that have 4-5 degrees of timing removed from factory values in the cruise range. 44-45 degrees of timing in a V8 is a lot for many newer engines. Old iron may well need that kind of advance but the real goal is to start spark later and finish combustion earlier and to get more usable power. If not using lean cruise mode be sure to try decreasing spark a degree or three in the cruise range. If decreasing timing shows rich O2 readings then go back and re-adjust VE. Drive again and check TPS to see if you're opening the throttle more than previously. Less spark, less fuel, and same or less TPS = more mileage.

    HTH
    Last edited by 1project2many; 03-04-2012 at 02:00 PM.

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    Quote Originally Posted by 1project2many View Post
    There's a point where you're past best power but you're not making knock.
    IIRC, this is also the zone that will mysteriously eat connecting rod bearings.
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    EFI GearHead ! EagleMark's Avatar
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    First you should tell what ECM and mask your using? I know it's a 1227747 $42. It has no way to measure knock to retard timing a little and give a reading like later P4 ECM which can get knock counts and remove 1 degree or 8 degrees for example. Much better to use the knock sensor for timing on these.

    Quote Originally Posted by RobertISaar View Post
    IIRC, this is also the zone that will mysteriously eat connecting rod bearings.
    I think you mean wrist pin bearings? Either way there is a point where your to far advanced and get no ping ot knock and loose power and lik Project said increase oil temp. The reason is the piston is absorbing all the heat and only oil is cooling piston. Bad on both fuel milage, power, wrist pin and conecting rod bearings.

    Before you start using the knock sensor as a guide you should make sure it even works correctly and you can run engine with no knock counts. A few years ago I had no knock counts, never changed timing from stock, when I added timing I got knock counts so factory timing is using most of what it has, now I have knock counts even if I take out 4 degrees? So I guess the 140K on motor is starting to make noise.

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  5. #5
    Fuel Injected! 1leg's Avatar
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    Thanks guys this is some good info.
    1993 RCSB 1/2, 350/4l60 Eaton locker 3.42-1. Drag truck ET 10.84 1/8mile. Build Thread
    1989 V2500 Suburban 350/th400, 4.11 gears, Tow truck, needs TBI 454 swap. Build Thread

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    IIRC, this is also the zone that will mysteriously eat connecting rod bearings.
    Very true. In my Cavalier turbo running $58, we had a cold stretch one winter and my marginal heater core wasn't quite up to the task of making heat. I was very, very busy at that time and couldn't see making time to change the core. Being a smart guy and knowing my stuff, I just said "I'll whip out the laptop and dial up a couple of degrees extra timing at light cruise to make more heat." It worked. But after two trips back and forth from work the low oil pressure light would come on at idle when the engine was warm. Not only did I end up changing the core but also the rod bearings and the oil pump as well. Some smart guy I was on that one.

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    Fuel Injected! JeepsAndGuns's Avatar
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    So theres a point in between good power and knock where you can kill a engine? Umm wow, how would one know when you are at this spot?

    1project, could your engine problem have been prevented if you ran higher octane fuel?
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    1project, could your engine problem have been prevented if you ran higher octane fuel?
    First off, was my engine problem really an engine problem? After all, I had a calibration properly tuned for the fuel I was using. I had logged thousands of miles on that calibration without worries. And I had chosen to alter the calibration in a way that would knowingly be pushing the limits of best tuning I could come up with. So what was the problem? Would higher octane fuel prevented the bearings from being used up with the timing settings in my modified calibration? Possibly. Would higher octane fuel have prevented the bearings from being damaged and needing replacement? No, probably not.

    Octane rating is just a measure of the fuel's ability to resist knock and this engine wasn't knocking. Now the way the octane rating is arrived at leaves a lot of variation in how a particular fuel behaves. So there's a chance the combustion propertiess of the fuel could have been slightly different, which might have generated a different pressure curve that didn't damage the bearings with only a couple more degrees timing. But remember that I was trying to make too much pressure, and I was trying to use that excess pressure to heat the coolant more than it was already being heated in very cold weather. So even if the fuel behaved very differently chances are that I would have altered timing to the point where the bearings suffered anyway. This engine was 9.2:1 compression running almost 8 psi boost provided by a small turbo running outside it's efficiency range on 87 octane fuel with no engine oil cooler. The reason too much timing took out the bearings so quickly is because it was a bit close to the edge to begin with. I just took it few steps closer those couple of days.
    Last edited by 1project2many; 03-05-2012 at 08:24 PM.

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