Adjustment position slipstream on Muffler of Kart

I have create a kart, i did try to adjustment slipstream/smoke usually on center backside kart position. for change on each position where muffler from kart has patched.
like adiumy, beagle, beastie, suzanne, tux. and great, i failed.
after give up, then i decided want to ask for find the answer.
like adiumy, beagle, beastie, suzanne, tux. and great, i failed.

after give up, then i decided want to ask for find the answer.