How to modify expansion chamber for more torque

Discussion in 'Performance Mods' started by jaguar, Dec 13, 2012.

  1. jaguar

    jaguar Well-Known Member

    All the expansion chambers sold for the Grubee engine were designed for peak rpm power engines that also have transmissions. They are the opposite of what is needed for our rides which, if you don't have a shift kit, need a broad powerband instead of a peaky one. Luckily it doesn't take a lot to modify your pipe to shift the focus from peak rpm power to wide range rpm power. If you are looking at pipes to buy one then try to find one with as close to these specs as possible: 6" long diffuser cone and 2.5" long belly.
    Just cut the baffle and weld in an extender as this diagram shows. That reduces and elongates the return baffle wave. That wave, at low and mid-range rpm, only fights against the return diffuser wave which results in less delivery ratio (ie: less power). It only is of service at top rpm when it serves to increase delivery ratio and compression. Modifying the baffle cone this way reduces the peak wave strength 60% and elongates the wave 33%. Here are the before and after wave graphs:
    Last edited: Dec 14, 2012

  2. Fabian

    Fabian Well-Known Member

    I love this kind of stuff.
  3. geebt48cc

    geebt48cc Member

    Yes, me also!~ I've got pipe much better now, but I'm sure I can make it even stronger.Uno, but it's now to the point where I've got to remind myself it's only a 3hp china made engine.?!

    ................but good is never good enough!!!!!~
    Last edited: Dec 14, 2012