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Thread: Spark table review/tune review - LS1 C5 Corvette with medium cam and FBO

  1. #1
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    Question Spark table review/tune review - LS1 C5 Corvette with medium cam and FBO

    Hi HPT folks,

    I would like the confirmation of a seasoned tuner to confirm if it's safe enough what I've done to my spark tables (High/Low octane are equal) and my current MAX Knock retard values for both PE and non PE tables. Latest tune and logs attached. Much appreciated.

    Long story short (sort of), after putting a medium cam, 42#injectors, and FBO (everything except I kept stock 853 heads) I had a local tuner dyno tune my car. A couple of iterations back and forth with him for drivability, and I never found myself fully satisfied so I took matter into my own hands and got the MPVI. I've been dealing with hesitation/misfire issues when launching off idle among other nuisances such as cambuck. After hours upon hours of datalogging, learning and tuning. I found the reason for my hesitation was a high, unwanted amount of knock retard "KR" being thrown on top of the spark table. I've been modifying my spark table based on logs on a constant, re-iterative process, making revision after revision after revision of my tune. Then I had an "ah-ha!" moment when I found the major key player of my excessive "KR". It was a torque management table (spark reduction) that wasn't zeroed out by the tuner. Another thing that made an improvement was equalizing the Max Knock Retard tables for both PE and Non PE tables. I set them both to 10 degrees so as the PCM changes between PE and non PE modes, it won't be jumping around with different KR. Max knock retard in PE was already at 10, and non PE was originally like 12 to 15 for parts of the table, and I just brought all these values to 10. I can say that it feels like it runs like a champ now, even aggressive off the line acceleration off idle, it doesn't misfire anymore or hesitate. I even took some a bit of timing out on key points that I saw some KR jump in WOT at higher loads (my tuner did a lot of "blanket timing" for a lot of areas, including peak torque).

    My tip ins at this point feel phenomenal too and spark map looks smooth and transitions pretty smoothly and WOT rips like hell!! Instant throttle response when I want it. I basically took the time to really pinpoint where tip in accelerations occur and added timing back (copied it back from the original dyno tune and smoothed it in with interpolation) only where it needed it, to make it snappier and more eager but not come in too early or low in grams/cyl so it wouldn't bring back the buck again.

    At this point, I just want a pro to review my spark timing tables and let me know if you see any areas of excessive timing. At this point I've spent already over 16 hrs of combined time spent on tuning, datalogging, and analyzing.
    Latest file and log attached. I don't want to too much timing where I don't need it (I'm concerned that maybe I went too aggressive on timing on near very low RPM and high load, but car does feel fantastic right now and doesn't hesitate).

    FYI: Mine is a manual 99'. LS1 5.7L with stock bottom end. I'm running 93 pump and I live in South Florida (sea level). My cam is JEGS/ELGIN/TRICKFLOW/SLOPPY Stage II .585/.585/228/230/112LSA, LS6 intake, FBO and catless, everything except stock 853 LS1 heads. 42#@58psi remanufactured injectors. K&N Cold Air intake and airbridge and Texas Speed 1-3/4 Long tube headers with X pipe. 3.42 final drive.

    Additional FYI: Anything fueling and airflow related I have not touched nor plan to touch until I get a wideband sensor. Fueling was on the money on WOT pulls done by previous tuner. Don't know about STFT's but the dyno's wideband AFR read 12.7 on those WOT dyno pulls, so I'm not touching fueling for now.
    Last edited by turabo87; 07-26-2019 at 01:13 PM.

  2. #2
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    I thought I might be asking for too much when reviewing my whole spark table. I'd like to clarify that my area of concern is that I might have commanded too much advance in low rpms and high load and this is the part I'd like for someone to review. I want to explain how I got here first: I found from just seat of the pants testing, that my engine just doesn't agree (hesitates and misfires) with timing below 15 degrees on low RPM (between 800-1200) and high load (the" bogging off idle" area). This is my issue with this: I know that those areas are of high load and high cylinder pressure therefore theoretically I shouldn't have so much advance to safeguard my engine, and the PCM seems to agree since it pulls timing (sometimes as much as 8-10 KR degrees) when I hit these values BUT my driving experience says otherwise. What I mean by this is that I feel the cam hates anything less than 20 degrees of commanded advance in these areas (it will hesitate and misfire with lower commanded timing), but I'm afraid the KR I get here when I run 20degrees of commanded advance might be from real knock. Can you give me your $0.02 on this? Assuming airflow and fuel is normal, what should be the typical spark advance range for off-idle (800-1200) and high-load for a medium cam like mine?

    PS: I figured out from "back-analyzing" the tune and comparing it to the stock tune, it looks like my tuner calibrated the car PURELY off MAF, and he kept dynamic airflow disabled and left EQ ratio set at 1.0 for high loads/high RPMs. As a matter of fact, he left my VE table actually completely stock. I'll have to tackle this some other time when I have the Wideband.

  3. #3
    Tuner in Training
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    I'm not an expert, but I have some experience with timing. I suggest you dial timing back from 400 rpm to 800 rpm to about 14 to 15 degrees of advance. Other than that have at it

  4. #4
    Tuner in Training
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    What is FBO?

  5. #5
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    Quote Originally Posted by mild7 View Post
    What is FBO?
    full bolt ons. To be specific: K&N cold air intake and airbridge, LS6 intake, TSP long tube 1-3/4 headers and xpipe (catless), and Magnaflow exhaust w/ bypass mod.

  6. #6
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    Yea this is what I call the "bogging area". Cam just hates low timing here but I guess better safe than sorry. I rarely hit this part of table anyway since it's usually an indicator of bad driving on my behalf (not enough throttle during clutch-out from a stop light), but when I do hit these values I don't want the engine to fall on it's face and misfire, which is what it typically does with timing at less than 20 here. I'll dial it back and try again.