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Thread: How much fluctuation is normal?

  1. #11
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    Quote Originally Posted by Danny Cabral View Post
    I'm gathering the parts to switch my TH350 to a 700R4. When I make the switch, I may look to see what I need to log driveshaft speed.

  2. #12
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    Quote Originally Posted by ChevyC10 View Post
    I made some changes to your GCF/tune, it should help: https://drive.google.com/file/d/1u-s...ew?usp=sharing
    Thank you very much! I'll try running it on Monday and report back. Kevin

    UPDATE: For some reason that config didn't sit well with the car, so I started over with the Wizard and a stock cam base calibration. I drove around for a few days to generate and apply a Learn Table before taking data. I've included two datalogs, one at 60 MPH and one at 70 MPH. Also the latest GCF. Please let me know if there's something obviously wrong here that would cause the fluctuations I'm seeing. Thanks! -Kevin
    https://drive.google.com/file/d/16hD...ew?usp=sharing

  3. #13
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    Have you checked for exhaust leaks? Have you tried any other Target AFR? You're still at 15. Maybe it doesn't like that. I always like to tune from rich to lean. Put your Target AFR in your cruise area to 14 and see if it makes a difference. Not every engine can run that lean. I run 14.7 at cruise, but I'm running sequential MPFI. When you make datalogs, make them longer. Drive it for an hour so we can see what it does at other RPM. You can never have too much info.

  4. #14

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    The datalogs you have provided look good. The fluctuation in AFR is not anything to worry about. My SBC likes to cruise at 16:1 AFR and it has a large cam, but to get the best results you just have mess around and see what makes the engine happy (Reading plugs will help.) I'm sorry to hear that the tune I gave you did not work well. The main difference in the tune I gave you, versus the Wizard is the scaling of the fuel map. The Wizard goes up to 16 psi of boost, which I do not think your engine will see in a N/A setup. If you want, I would recommend changing the Target AFR in the tune I give you, because in the long run once the Sniper EFI is done its self-tuning, you'll have a better tune.

  5. #15
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    Quote Originally Posted by ChevyC10 View Post
    The datalogs you have provided look good.
    I disagree. Look at the MAP in the second log. Look at how it fluctuates. The TPS is steady, but the MAP is fluctuating. He may not be feeling it, but that engine is surging. Probably because it's too lean. That's why we test different things.

  6. #16
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    I will try remapping the cruise portion of the table to see what 14.0 AFR does to the surging.

    Another surging issue has reappeared just above idle. When I open the throttle to 2-4% TPS, is begins a deep surge where it's running fine, then almost quitting. If I bring it to idle, the problem does not exist. I'm not sure what's causing this, but I'm wondering if I have either an induction leak or an exhaust leak, and if I had either of those how it would present in the data. I'm still using the clamp-style WBO2 sensor, but it looks like a sound install. I guess I should look into that next? Thanks for all of the advice! -Kevin

  7. #17

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    Sorry I missed that in the datalog. So it's only surging at 70 MPH at 2700 RPM, but not at 60 MPH at 2400 RPM with the same AFR & timing. Are you using a dual-plane intake? It looks like a case of poor fuel distribution. You "should" not have a problem running at 15 AFR, but if some cylinders are not getting the same AFR, than you will have a problem.

    Your "deep surge" could be the CL Comp adding & pulling fuel to get the Target AFR. Try to keep an eye on your AFR and see if it's changing with your surging.

  8. #18
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    Quote Originally Posted by ChevyC10 View Post
    Are you using a dual-plane intake?
    Yes I am. It's an Edelbrock Performer RPM. Could this be the problem? Thanks, -Kevin

  9. #19

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    You will get the best results from using a single-plane with throttle body injection. Or I have heard of people solving this issue with a spacer on their dual-plane.

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