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  • WOT tuning question

    I am trying to tune my MS1 set up as fuel only on my BBC. It is port injected, 60#/hr injectors, etc. As I look at the graphs from each run down the quarter, I am graphing RPM, AFR, and MAP. What I am seeing is that the AFR goes from around 12.3-12.5 in second gear to just under 12 (say 11.9) in high gear. Is this normal? What do you normally shoot for on AFR and where? I was thinking I could get the same AFR for the same MAP and RPM in all gears, but it looks like it is different.

    Thanks,
    Why think when you can be doing something fruitful?

  • #2
    Compare your Pulse Widths (PW) to your AFR to see if something funny is going on with the AFR change between the gears. If the Pulse Widths commanded are the same at both RPM and MAP, then I'm not sure what the issue could be. There should be a PW change indicating a change in the engine's volumetric efficiency and how air is getting into or out of the engine. This could be due to several factors, like higher under hood temperatures which lowers the density of the air going into the engine, or some other air speed issue around the car and exhaust.

    I'm not expert tuner, but I've leaned my Buick out to 13.0-13.5, but you know what they say, lean is mean, and could also get you into trouble. Technically, longer the engine is loaded up it is better to go richer to keep the combustion temperature down and not torch pistons or burn valves.
    Escaped on a technicality.

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    • #3
      Might it be just more "load" on the engine in high gear.. making the engine run through the rpm range lasyer than the last two gears. and the map expecting the engine rpm to be the same in all gears at the same plotted time between. it's feeding it as if, it's rpm rise is (exp) 200 rpm per tenth of a second.. but in high gear the engines rpm rise is 200 rpm per 1/5th a second..
      I'm totally new to all this and still wrapping my fat head around it all.. so I might be way off..

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      • #4
        I have noticed this on my MS3X also. I haven't been able to tune this motor much in the higher RPMs but using the VE Analyze it is reducing the VE numbers in the higher RPM cells.
        1968 Plymouth Barracuda Formula S 340 with a 360
        1997 Jeep Cherokee off road toy/driver. lifted, lockers, stroked 4.0

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