Page 1 of 2 12 LastLast
Results 1 to 10 of 12

Thread: Acceleration AFR Spike - Review

  1. #1

    Default Acceleration AFR Spike - Review

    I've attached a zip file with five datalogs of varying acceleration and the Config File from the cruise. I'll do more driving and datalogging tomorrow with WOT included. I've lowered the AE vs TPS RoC .1 each time I take it out and it's slightly helping. The difficult part about the tuning is when I'm approaching boost. I'm adjusting timing to see what it likes so the values are still subject to change. I'm open to all suggestions and I greatly appreciate the help.

    The setup:
    -93 octane fuel
    -385 SBC
    -10:1 compression
    -Canfield heads 195 with 65cc
    -Crower 00484S cam
    Duration intake/exhaust 284°/286°
    Lift intake/exhaust .544"/.555"
    Lobe Separation Angle 114°
    -Dart 2 Sportsman Intake
    3000 stall converter
    TCI full manual valve body
    -3.73 rear gear
    -275/60/15 tire
    HyperSpark box, coil, distributor.
    D1SC ProCharger 5 psi.
    Intercooled 31"x12"x3" with 3" piping.
    Attached Files Attached Files

  2. #2


    Hi. By looking at the Config File, the base map has RPM of 500-8000. Looking at Target Idle and cam specs, this would be more suited having 700-6500. Also, looking at Target AFR, the psi ranges from -11.6 to 16.0. You said you are running 5 psi of boost. I don't know how much vacuum your setup makes, but I'm guessing -9 psi to 7 psi would do the trick.

    With doing this to your Base Fuel Table, Target AFR and Base Timing Table, it'll use more of the whole table. And you have more freedom fine tuning Target AFR in your cruise/accel area.

  3. #3


    Cwathne, thank you for taking the time to look. I've left the ranges fairly broad until I can do more WOT runs to see how much of the tables are being utilized. Once I have a better idea of acceleration & deceleration, then I can tighten the table ranges a bit. I will post more datalogs after some drive time today.

  4. #4


    You're welcome. If you don't want to adjust your tables yet, what you can do is to set a more static Target AFR were your MAP & RPM is at acceleration from the logfiles. Right now it's jumping across different Target AFR. It'll have an easier time tuning a static AFR in that area. Maybe that will make your actual AFR more stable.

  5. #5


    I see what you mean. I've been so concerned with keeping everything smooth that I've varied the AFR in that area. I've adjusted timing and will be taking it out shortly. I have put the AFR deep in to the safe zone, so once I start pulling fuel I hope it will stabilize.

  6. #6


    Attached is today's data logs with Config file I have adjusted. I am making slight changes so I do not lose track of what is helping. Pulling timing under boost made a very noticeable difference. I pulled a little more to see how it reacts.

    No WOT runs were made today.
    Attached Files Attached Files

  7. #7


    Is the car stumbling or experiencing poor performance in any way, or are you just seeing a blip on the datalog? Please describe the driving issue you're trying to solve.
    69 Camaro
    400 SBC, ProCharger D1SC

  8. #8


    Under partial acceleration, it will slightly stumble after the lean spike until it clears up. When I shift at higher RPM, it will recover much faster and not be as noticeable. As I slowly move the AE vs TPS RoC lower, it's making a difference to where it's not as high. When the stumble first started, the AFR would spike to 16+. I started a new Config File, reset the timing table and adjusted the AFR table. So far everything is moving in the right direction. Thanks for the help.

  9. #9


    I looked at a couple of the datalogs, but admittedly not all of them and I'm struggling to see a "lean spike". Both the datalogs I looked at never saw a reading above 14.8. That's not what most would consider a lean spike and I doubt very seriously is your issue.

    I'm curious why you have such a rich cruise AFR? In the high 11s to high 12s. Most people run minimum of 13.5 and upwards of 15+ for cruise. I run 14 at cruise with my ProCharger setup. It's true you tune boost richer than N/A, but that's just in the boost areas. In the vacuum areas of the table tune it like you would an N/A engine.

    Also, your timing is extremely low IMO. Small block Chevys love timing. One datalog I looked at had a max of 24° and a min of 19° at cruise. Cruise timing for a small Chevy is typically up into the mid to high 30°s. I cruise mine at 38°. Low timing will for sure cause a stumble.

    My advice is add timing in the NON-boost areas. Leave the boost areas alone for now. But do it gradually. We don't want to blow anything up. In the cruise area you could easily jump to 30° or more. The added timing will have a big impact on tip-in I bet. Are you laptop tuning?
    69 Camaro
    400 SBC, ProCharger D1SC

  10. #10


    Greg, I greatly appreciate your input! I've been guessing in the dark as to what the engine wants, since I changed the cam and added the ProCharger so your words are very encouraging.

    I will find an older datalog where it would spike above 16 AFR and was very noticeable.

    I adjust the timing and Base Fuel Tables with the laptop and datalog while overlaying on the Config File. I'm looking to dyno tune it for the most reliable tune and datalogging.

    As for the timing, I'll step it up and see what it likes. You're right on the cruise timing, especially when I'm in overdrive. I'd like to find the "agreement" spot with the AFR & timing. As I make timing changes it seems to be smoothing the AFR in certain areas.

    The low timing is due to the higher compression, but that's me being paranoid. I'll make your suggested changes in the right area. I pulled more timing under boost and it responded well, but that was just a measure with the seat dyno. Thanks again!

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
About us
Holley has been the undisputed leader in fuel systems for over 100 years. Holley carburetors have powered every NASCAR® Sprint® Cup team and nearly every NHRA® Pro–Stock champion for four decades. Now, Holley EFI is dominating the performance world as well as our products for GM's LS engine. Holley's products also include performance fuel pumps, intake manifolds & engine dress–up products for street performance, race and marine applications. As a single solution, or partnered with products from other Holley companies - Hooker Headers, Flowtech Headers, NOS Nitrous, Weiand, Earl's Performance Plumbing, or Diablosport - Holley products can give you the edge you need over the competition.
Join us