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Thread: Basic Steps to Tuning?

  1. #1
    Carb and Points!
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    Basic Steps to Tuning?

    I dropped a 383 into my '90 Corvette, which someone was helping me tune. Due to a series of problems continually throwing the tune off, he threw in the towel, so I'm going to finish the tune on my own. I've done a lot of research, and I'm a quick learner, so I think I understand the concepts pretty well. However, knowing how much a mistake can cost me, I want to make sure I have everything straight. Here are the steps as I understand them:
    1. Datalog, adjust VE table values, and repeat until BLMs are all within a point or two of 128.
    2. Set deceleration fuel cutoff
    3. Slowly bump up Closed TPS Spark Advance values in each cell until datalogs show knock retard there, then decrease it a point or two in that cell; find max for each cell
    4. Repeat process for part throttle (Main Spark Advance table up to 90 kPa)
    5. After making sure BLMs are correct and there is no knock retard for other circumstances, set advance for WOT

    Notes:
    • WOT AFR should be richer, cruise AFR leaner
    • All tables (whether in the BIN or datalog) should show consistent trends, not sudden spikes
    • Too much advance can decrease power before getting to the point knock is seen
    • Datalogging to set main VE and spark advance tables needs to be done in closed loop

    Questions:
    • If a datalog doesn't have a value for a BLM cell, I just extrapolate the VE from adjacent values?
    • When do I set open loop change to AFR vs coolant temp and MAP? Once I'm done with everything else?
    • My VE is pretty much maxed from 3200-3600 RPM at WOT, so the guy helping me suggested changing injector flowrate to compensate. But from what I've read, a VE that high on gen 1 SBC is pretty abnormal--you guys think there's a problem there?
    • I read PE mode must be disabled to get BLMs at WOT since PE puts it into open loop; however, my datalogs show BLM values for WOT. Why the discrepancy?
    • How many spark advance cells should I change at a time?
    • Are there any other tables/scalars/flags I need to adjust?

    As an aside, how the heck do you add line returns in a post? I've tried 3 different browsers, I've tried multiple returns in a row, I've tried BBCode... everything I try ends in line returns being replaced with spaces! The only way to get around it was to take advantage of lists' inherent formatting.

  2. #2
    Super Moderator dave w's Avatar
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    For $8D I use the attached spreadsheet to tune with. Intermediate to advanced Excel skills required. dave w

  3. #3
    Carb and Points!
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    That's really helpful, thanks! I thought about making something like that but somehow it didn't occur to me that you could copy from TunerPro tables into Excel and vice versa. Does my understanding of the overall tuning process look right to you?

  4. #4
    Super Moderator dave w's Avatar
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    Quote Originally Posted by 90Vette View Post
    Does my understanding of the overall tuning process look right to you?
    Your tuning plan is good. I usually wait on adjusting the timing table until the BLM's are close. I think +/- 5 BLM's (123 ~ 133) are acceptable. Once the BLM's are close, the timing and other drive-ability issues can be worked out. I usually don't have to adjust DFCO. I generally change one or two drive-ability parameters at a time, after the timing (knock) and fuel tables (BLM's) are close, to avoid headaches. If you have intermediate to advanced Excel skills the attached VE Correction spreadsheet is a very helpful "tool" for BLM tuning. I usually have to "Smooth" adjacent VE cells to get a good tune. ... dave w

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