Re: Stock moby 50v mod question r/t blunderbuss

Rebel Moby /
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The cross section area of the carb is basically the area of the narrowest part:

SHA14:12 is necked down to 12mm inside so that is 113 sq.mm (area of a circle is 3.14xradiusxradius) multiply the area by 60% gives you 68 sq mm. Reverse the area formula to find the target size (diameter from an area is 2xsquare root of (area/3.14)). That gives you 9mm as the starting point which would be optimum as a expansion chamber but for a stock exhause it is design more as a silencer so you would need to go for containment management rather then reversion.

To experiment with your set up then you would make a temporary metal plate to replace the silencer section of the exhause and drill a 9mm hole as an exit. Ride around and the performance would be slightly better then stock but lots noisier. Make the exit hole slightly bigger and ride again to check performance. Go like that making bigger n bigger holes until there is no more improvement in performance.

Measure your new exit hole size and source some tubing with that inside diameter and make a permanent back plate or modify the original plate to accept the new exit pipe. You want at lease 40mm or 1.5 inch inside the blunderbuss so it can deaden the sound and not get neighbors hostile every time you ride. If you need to hush it more then you can cap the inside portion of the pipe and turn it into a piccolo by drilling multiple small holes in the side wall of the tube so it diffuses the sound.

I found with 12mm carb on a stock AV7 it likes approximately 11mm or 85% as a outlet on the blunderbuss. Strangely enough a 14mm carb seems to like 10.5mm on a stock motor which is 56% so you have to play with size a bit.

Back to the maths, no one likes to do long calculations so here is a site to calculate circle areas...

http://www.rkm.com.au/calculators/calculator-circle-sphere.html

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Subject Written By Posted
  Stock moby 50v mod question r/t blunderbussTopic by: Rachel LGN Rachel LGN 05/25/12 02:50PM
  Re: Stock moby 50v mod question r/t blunderbussRe: birdsy —— birdsy —— 05/25/12 03:14PM
  Re: Stock moby 50v mod question r/t blunderbussRe: Born to be WillD Born to be WillD 05/25/12 03:45PM
  Re: Stock moby 50v mod question r/t blunderbussRe: Rachel LGN Rachel LGN 05/25/12 04:02PM
  Re: Stock moby 50v mod question r/t blunderbussRe: Rebel Moby Rebel Moby 05/25/12 04:59PM
  Re: Stock moby 50v mod question r/t blunderbussRe: Mel Dyer Mel Dyer 05/25/12 06:06PM
  Re: Stock moby 50v mod question r/t blunderbussRe: Rachel LGN Rachel LGN 05/26/12 01:36AM
  Re: Stock moby 50v mod question r/t blunderbussRe: Rollo Tomassi Rollo Tomassi 06/04/12 10:16PM
  Re: Stock moby 50v mod question r/t blunderbussRe: Rachel LGN Rachel LGN 06/08/12 03:38PM
  Re: Stock moby 50v mod question r/t blunderbussRe: Rebel Moby Rebel Moby 05/26/12 10:16AM
  Re: Stock moby 50v mod question r/t blunderbussRe: Mel Dyer Mel Dyer 05/26/12 11:52AM
  Re: Stock moby 50v mod question r/t blunderbussRe: Rebel Moby Rebel Moby 05/26/12 12:08PM
  Re: Stock moby 50v mod question r/t blunderbussRe: David Gabert David Gabert 07/21/13 09:07PM
  Re: Stock moby 50v mod question r/t blunderbussRe: Rebel Moby Rebel Moby 07/21/13 11:26PM
  Re: Stock moby 50v mod question r/t blunderbussRe: David Gabert David Gabert 07/22/13 12:05AM
  Re: Stock moby 50v mod question r/t blunderbussRe: David Gabert David Gabert 07/22/13 12:23AM
  Re: Stock moby 50v mod question r/t blunderbussRe: Rebel Moby Rebel Moby 07/22/13 08:50AM
  Re: Stock moby 50v mod question r/t blunderbussRe: David Gabert David Gabert 07/22/13 10:13AM
  Re: Stock moby 50v mod question r/t blunderbussRe: Sean Berg Sean Berg 08/03/13 01:24AM
  Re: Stock moby 50v mod question r/t blunderbussRe: Rebel Moby Rebel Moby 08/03/13 09:22AM
  Re: Stock moby 50v mod question r/t blunderbussRe: David Gabert David Gabert 08/11/13 07:56PM

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