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Thread: Tuning for Low Compression

  1. #41
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    I should say...multiply the startup airflow by 1.76 in the 0 seconds column...then sorta smooth that difference into the rest of the table based on run time...so multiply each column by less and less. Essentially you can use that table to do the same thing your foot is doing when you pedal it...giving it more air to fire up.
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  2. #42
    Senior Tuner 5_Liter_Eater's Avatar
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    Quote Originally Posted by MikeOD View Post
    It's also worth saying...if you changed timing THAT much, you probably should now revisit your airflow model...a small change to timing won't have much affect on that, but a big change will definitely throw that off some.

    Does the car sound like it's struggling to crank or is the starter turning it easily, it just doesn't fire?
    I've already lined out the VE table again. It fell into place easily.

    The starter isn't struggling, it's just cranking and sputtering and I have to floor it to get it to fire.
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  3. #43
    Senior Tuner 5_Liter_Eater's Avatar
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    Quote Originally Posted by MikeOD View Post
    Based on your idle airflow table...you're commanding ~1.76x the stock idle airflow in order to idle (at 850 RPM). That's seems reasonable to me given the larger engine, larger cam, and less timing at idle...that said, you're commanding completely stock startup airflow and startup spark advance.

    I'd try taking the Startup Airflow table (Idle Startup Airflow vs. ERT vs. ECT) table, and multiplying it by ~1.76...you might then find the startup flares way too hard/high, but at least you'll see you're on the right track...you'll probably wind up with less than stock times 1.76, but more than stock by a decent amount. I think you're especially going to notice a startup flare because you've got the startup flare control spark table zero'd out. I've found if you've got too much startup airflow and then the spark is too agressive in the flare control table, the car will oscillate RPM and struggle to idle initially...might even stall...so you need to balance the airflow and the spark control.

    If it sounds like it's turning over really really easily, you could also try more cranking advance...but you might not need to after the airflow tables.
    I'll try multiplying the startup airflow table first. i'm not sure how it got that low because I know I experimented with jacking it up since I was having to pedal it. And ~doubling it didn't seem to make a difference which I thought was odd.

    Given the gross amount of spark added to the main table and the favorable outcome, I would like to try adding a bunch of spark to the cranking start. I need to take a new startup log but I was seeing very low cranking spark and disabled the startup flare to see if I could get it higher.
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  4. #44
    Advanced Tuner jakebdb56's Avatar
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    Quote Originally Posted by 5_Liter_Eater View Post
    I've already lined out the VE table again. It fell into place easily.

    The starter isn't struggling, it's just cranking and sputtering and I have to floor it to get it to fire.
    Did you scale cranking VE?

    If you have to floor it to get it to fire, it may be doing a flood clear (as you floor it) since it has too much fuel without being scaled.
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  5. #45
    Senior Tuner 5_Liter_Eater's Avatar
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    No I haven't tried that yet either Jake. I will.
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  6. #46
    Senior Tuner DSteck's Avatar
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    Not scaling cranking VE will do it. Set it all to 50. Noob.

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  7. #47
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    Quote Originally Posted by jakebdb56 View Post
    Did you scale cranking VE?

    If you have to floor it to get it to fire, it may be doing a flood clear (as you floor it) since it has too much fuel without being scaled.
    Yeah, when he said pedaling it, I thought he meant fluttering it...flooring it and pedaling it aren't the same thing lol.
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  8. #48
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    You've got a very abrupt spike in your timing map between 3000 and 4000 RPM and 0.40-0.44 g/cyl. Might want to smooth that in to the rest of the map.
    Last edited by MikeOD; 08-14-2013 at 10:35 AM.
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  9. #49
    Senior Tuner 5_Liter_Eater's Avatar
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    So because I like to make things difficult I changed a bunch of stuff at once. I bumped startup airflow by 30%, set cranking spark to 20 across the board, put the flare control back to stock, and set the cranking VE to 50%. Cold start it started right up, no throttle needed. I did it a few more times and it didn't fire quite as fast but it still started what I would consider well and no throttle input needed. I'll try a hot start later tonight.

    Thanks for the help so far. I've been struggling with this stuff lately for some reason. Too many have killed the brain cells that used to know this stuff.
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  10. #50
    Advanced Tuner jakebdb56's Avatar
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    Sweet! We're all here for moral support lol.

    Now just to figure out your fan problem...

  11. #51
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    Quote Originally Posted by 5_Liter_Eater View Post
    So because I like to make things difficult I changed a bunch of stuff at once. I bumped startup airflow by 30%, set cranking spark to 20 across the board, put the flare control back to stock, and set the cranking VE to 50%. Cold start it started right up, no throttle needed. I did it a few more times and it didn't fire quite as fast but it still started what I would consider well and no throttle input needed. I'll try a hot start later tonight.

    Thanks for the help so far. I've been struggling with this stuff lately for some reason. Too many have killed the brain cells that used to know this stuff.
    How did the hot start go? I am running a destroked 6L with about 9:5:1 compression and I am also having a hot start issue. Cold start it will fire right up and even if its hot and I shut the car off then back on a minute or two later, it will fire right off... but if I wait awhile it will crank and crank and crank then if I give it some pedal it seems like it will start.

  12. #52
    Senior Tuner 5_Liter_Eater's Avatar
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    It starts pretty well hot too.
    Bill Winters

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