Do you want a 100cc engine?

[Arnage]

I started out in the 100cc kt100. Verty fun to drive. I say yes.

[top kart gore]

You need a kt-100 with a patriot 2 disk clutch with ability to adjust cluth and carb (carb on the fly would be awsomely realistic) No front hand brake and a 30mm tube chassis and your set i would get soooooo many more people to join if you got that going and no matter what people say 100cc is not dead they are actually still very common in th usa. They are not dying just a bunch of unfair rule against them so people go to the 4 strokes. Oh and make sure YOU DO NOT RUN PIPE RUN THE 4 HOLE CAN this will make the true 100cc feel come out and you will feel the diference. This would be a fantastic addition to the sim.

[Buzzard12]

I didn't know you could get a four hole can for them. Not in Australia at least.

[LIAM-36-AUS]

I didn't know you could get a four hole can for them. Not in Australia at least.

what is a four hole can ? 

[EVO]

It is the sportman class in the U.S.  affordable, reliable, and useful up to the pro ranks,  this makes it very competitive.  Most drivers switch to TAG as they get more experienced. TAG is like KF2 power levels, but with non manual operated front brakes and a weight penalty for having front brakes.
The superbox or supercan class (4 holes)  use this tiny can shapped exhaust to restrict the rpm and prolonging the life of the engine (14,000rpm 14hp vs  16,000rpm 18hp KT100 pipe.  ).  The class is about being smooth, but aggressive.

if you want a real karting experience with out all the complexities get a used ICA, FA , or FSA  engine they are 100cc and over 30hp direct drive (no clutch power loss)
You can can get a great deal on them, but might not last too long ($300 for just an engine)

the Iame Parilla Sudam is 38hp (stock)  it is basically a Iame Parilla ReedJet (ICA 100cc) bored and stroked to 125cc. 
Its awesome! i believe they use it exclusively in Brazil though. It is homologated until 2018!
"There are even stories about them being tuned to produce over 50hp, which is just mental!"
Source:  http://www.karting1.co.uk/news/news/the-best-kart-engine-youve-never-heard-of-iame-parilla-sudam-125cc-tested/
http://www.iame.it/en/products/iame-karting-.html?section=motor&id=28&pass=si