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M8 EFI to Carb conversion

  • speedzter
    speedzter
    22 days ago
    I found this a while ago, and thought it would be handy for my M8 powered FXR daydream !
    I had previously looked at their Twin Cam EFI/Carb setup when I was doing the 
    VW beetle to Twin cam engine conversion .

  • John.R
    John.R
    22 days ago
    Altmann make good quality gear. Their standalone system for twincam is much much better than the Thunderheart system people always talk about. That thing is basic as fk and a step back from an Evo ignition.


    Biggest issue with M8 conversion in FXR is the extensive frame mods, but more n more products are coming out to overcome that hurdle, like weld in motor cradles etc.
  • Hilly
    Hilly
    22 days ago
    Don't bite me here, this is just a question, could you do this to a twin cam and get it registered? 
  • speedzter
    speedzter
    22 days ago
    Do you mean a legal Carb conversion ?
    Technically you would need it to be engineered and pollution tested.
    But in reality, I don't think anyone would know the difference .

    The Altmann supplier is german based, and they are quite strict, but can get away with it if it tests OK .

    Have a look at their little device to aid pollution testing:
    http://www.altmann.haan.de/L1/
  • Hilly
    Hilly
    22 days ago
    Quoting speedzter on 29 Jan 2026 03:08 AM

    Do you mean a legal Carb conversion ?
    Technically you would need it to be engineered and pollution tested.

    But in reality, I don't think anyone would know the difference .

    The Altmann supplier is german based, and they are quite strict, but can get away with it if it tests OK .

    Have a look at their little device to aid pollution testing:
    http://www.altmann.haan.de/L1/

    Well bugga me! It's a calibrated intake manifold leak 😁
    I'm going to save these links, could come in handy down the track, thanks 👍
  • speedzter
    speedzter
    22 days ago
    Quoting John.R on 29 Jan 2026 01:12 AM

    Altmann make good quality gear. Their standalone system for twincam is much much better than the Thunderheart system people always talk about. That thing is basic as fk and a step back from an Evo ignition.



    Biggest issue with M8 conversion in FXR is the extensive frame mods, but more n more products are coming out to overcome that hurdle, like weld in motor cradles etc.

    I ended up using the Thunderheart Ignition, it was a fair bit cheaper .
    I'm not sure the Altmann is better , they both have adjustable Ignition curves and don't use a MAP sensor .

    The Thunderheart at least is programmable with windows software :
    https://thunder-heart.com/Tech%20Service%20PDFs/EI5011.pdf
  • tussuck
    tussuck
    22 days ago
    Just make sure you get the right cable for the unit.... none of those cheap knockoffs.
    I love my unit on my 883L and it takes 2 secs to find a canned map for the bike when I need to.
    Does it have autotune and wideband support?
  • John.R
    John.R
    22 days ago
    How TF do you autotune a Carb?!
  • tussuck
    tussuck
    22 days ago
    my sporty is efi and the fxr is carb.  

    for the fxr i installed a wideband O2 sensor and used a Zetronix unit to record rpm AFR mix.  doing test runs at 1/8, 1/4 throttle etc bought the carb in pretty damn close.  then i went richer to just play it safe -- she was turboed at the time 
  • John.R
    John.R
    22 days ago
    Yeah im familiar with the approach, Ive not seen a wideband an auto tuner built into a carbd ignition system though.
  • Stuart
    Stuart
    21 days ago
    Quoting speedzter on 28 Jan 2026 11:59 PM

    I found this a while ago, and thought it would be handy for my M8 powered FXR daydream !
    I had previously looked at their Twin Cam EFI/Carb setup when I was doing the 
    VW beetle to Twin cam engine conversion .

    Did you have a thread about the VW to Twin Cam conversion? It's not ringing any bells - but I haven't been around that long. Nothing is showing up when I search - possibly I'm not looking hard enough. I'd be interested to see it.
  • speedzter
    speedzter
    21 days ago
    The VW was my brothers project, I just setup the wiring/ignition and Carb.
    It was based on a German adapter housing that he imported, and had a few bits machined to our specs to adapt
    the VW clutch to the Harley Crank output shaft.
    It was setup in a rust bucket VW with the plan to do a motor refresh and get it registered in a decent car,
    but like many projects, it has stalled !
    We didn't really document much of the build.
    The initial starting video got over 700 thousand views .


  • Hilly
    Hilly
    21 days ago
    Best sounding Beetle I've ever heard, impressive mate, clever buggas 👍
  • Stuart
    Stuart
    21 days ago
    Quoting speedzter on 29 Jan 2026 10:14 PMedited: 29 Jan 2026 11:02 PM

    The VW was my brothers project, I just setup the wiring/ignition and Carb.

    It was based on a German adapter housing that he imported, and had a few bits machined to our specs to adapt
    the VW clutch to the Harley Crank output shaft.
    It was setup in a rust bucket VW with the plan to do a motor refresh and get it registered in a decent car,
    but like many projects, it has stalled !
    We didn't really document much of the build.
    The initial starting video got over 700 thousand views .


    video
    Very cool !
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