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thundermax - what is it and why?

Discussion in 'Cruisers' started by Puff, Jan 22, 2009.

  1. HI folks,

    Went in to HD Performance last week and got some info that left me more confused than helped given a complete lack of all mechanical knowledge on my part.

    Essentially I was recomended there after complimenting a bloke on the sound of an exhaust from HD Sportster 883 (same as my bike). I got a quote for the exhaust but the bloke told me if that was all I did it would run lean, backfire and sound like sh!t. He then told me I should get a thundermax at least with the pipes and start from there.

    Mechanically the 883 is still stock standard and has 15k on the clock.

    My questions:
    Why would the bike run bad if the pipes are changed from standard?
    What is the Thundermax actually for?
    If I don't have the Thundermax could it damage the bike and will it really run bad?

  2. An engine is basically an air pump.
    It sucks cool air in through the filter, does something magical involving a rapidly burning liquid, and spits hot air out the exhaust really fast (the same air as went in, but now taking up more room because it's hot).
    As by-products, it creates some heat, noise and rotational energy, which is handy because the heat keeps your legs warm, the noise warns people you are coming and the rotational energy can be sent to the rear wheel to make the bike move!
    There's quite a delicate balance of air and petrol involved in making this happen and if you mess with that balance you could make it either be not as efficient or stop altogether.

    Short answer, if you allow the air to go out faster at the back without adjusting the amount of air going in the front, you unbalance the finely tuned system.

    The Thundermax is a replacement EFI system; the computer that tells the bike how much fuel to put into the cylinders. It'll help adjust that fine balance to take into account the extra air flow from your new pipes.

    Running lean can damage the bike due to it getting too hot. Running rich wastes fuel, gums the works up with carbon and leads to backfiring. Neither is good and having the Thundermax or equivalent is a really good idea.

    Basically, I wouldn't mess with the stock setup unless I was willing to go the whole hog, front to back.
    1) Increase the air flow going in
    2) Increase the air flow going out
    3) Put on a new EFi system
    4) Have the bike properlly tuned on a dyno

    It'll sound better, produce more power, run smoother and potentially be more fuel efficient.

    Of course, by the time you've done all these things, it might have been better financially to simply sell your current bike and get a more powerful model instead.
  3. Thanks Mountaineer - I get what you're saying. Add to that I already have my sights on the next bike for next summer, I'll park the funds and do all that on the new one.

  4. Mountaineer,
    What a great reply! Clear and to-the-point and entertaining to read!

    Well done

    :applause: :applause: :applause: :applause:


  5. My questions:
    Why would the bike run bad if the pipes are changed from standard?

    - If you only installed a set of "slip-ons" the ECM (Electronic Control Module) would probably be able to adjust the air-fuel ratio sufficiently. This is not a guarantee though as the ECM has only limited scope to adjust your air-fuel mix.

    What is the Thundermax actually for?
    - it's an automated system that monitors the engine inputs and outputs (fuel and air). It is a poular systme as it allows a wide range of tuning adjustments (so it can handle a number of changes to the engine or exhaust) and doesn't require a HD tech to tune the engine after you make a modificaiton. It does have it's limitations (see www . hdforums . com) and there are a number of alternate systems to ensure you get the right air/fuel mix. Some people love it, others don't. The system replaces your standard HD dash controls with a Thundermax panel which IMO is extremely ugly.
    - Alternatives to Thundermax are (not an exhaustive list):-
    - 1 - Vance & Hines Fuelpak
    - 2 - Power Commander III
    - 3 - HD Screaming Eagle Race Tuner (SERT)
    - 4 - Big Joe's Choppers (in QLD) offer a solution for installing aftermarket pipes, speak to Mick
    - 5 - The new HD SERT, the name has changed for 2009 models.

    Also be mindful that most dealerships in Oz aren't particularly skilled with multiple products and they tend to specialise. Make sure you get a tech who knows all about it before you ask them to install it (if you don't do it yourself).

    If I don't have the Thundermax could it damage the bike and will it really run bad?
    - if you install a full pipes system then very probably yes you will damage the engine as you'll increase the airflow through the system without increasing the fuel inputs. This creates a lean air-fuel mixture which when ignited creates a hotter ignition temp (more air = hotter) which will prematurly wear engine components out. You need to ensure you're fuel input is increased and Thundermax or any number of other products can do this for you. The HD stock settings for air-fuel are on the lean side to begin with (thanks to the EPA emission requirements) so ideally even without changing any exhaust parts your bike would benefit from being tuned to run richer (and it will have more power and run better). Getting the right air-fuel mix can take some experimentation.

    Get onto HDForums . com and read everything you can there - there is a welath of information available.
  6. If i could just chime in here because it seems a reasonable place to throw it in, even though it isnt exactly what the OP was asking for.

    I have been thinking about the same things for my VT750c2, and i dont know where to go, or who to speak to about it.

    Any thoughts? and price guides for the ecu?