The extractors that I source do come with a 1.75" outlet..
I've modded the extractors to 2", 2" hotdog under the passenger seat, then 2" all the way back to a Redback 2" straight thru muffler. Sounds good and none too noisy.
I also used a tri-chamber muffler on the rear, also sounded good. Pretty quiet.
Also on my KE30 I had extractors and 2" all the way back to a 2" straight thru muffler. That was WAY too loud. Never again. :bash:
The KE30 was a stock 4K with a 3K head and stock carby.
Just go 2" with a hotdog resi under the front seats, and a tri chamber at the rear. Will be good, and you can always go to a straight thru if you want more noise.