you could do both... but without a exhaust you will lose alot of power
the exhaust is there to pressurise the fuel tank and to give maximum performance from the engine

An airplane engine wouldnt go very good either.... if you look at the difference in RPM ranges between a RC car engine a RC plane engine you will see the the car engine tops out usualy at around 28,000 + rpm
the plane engines usualy only go to about 17 000rpm