4 strokes are used for aircraft a lot, smoother delivery of power one of the advantages and more torque letting you swing big props
http://www.osengines.com/engines/osmg0830.html
this is smaller than the spec given and costs about £130, OS are the masters of these engines in the rc plane world so the tech is there there just needs to be demand to encourage a differant power delivery for cars. One newish development is you can now run electronic ignition on a nitro 4 stroke which means no more glow plugs and it can't be a massive leap to convert it over to gas use.
dedicated gasoline engines are around but not so small sadly mostly used in large scale but they sound so good in multi banks
listen to this radial engined monster