Suzuki F6A: 657 ccs of fury for a kei car

[Calypso]

These days 1kr is also available turbocharged from factory: 1KR-VET. It's very hard to find any details on the internal differences to the N/A model. But you are right, it's easy to find higher output engines. Featherweight turbo 3-cyl could however be an attractive alternative for bike engine conversions. You could get similar output/weight with real rwd transmission with reverse gear and adequate charging system. 1kr-vet puts out 100hp/100lbft in factory tune below 6krpm, so there should be room for more.

[BLSTIC]

If you want a truly indestructible but exceedingly rare three cylinder, Daihatsu made the CB70/80. Based on the CB23/50/60/90 architecture with larger main bearings, dohc, efi, forged rods and pistons and 7:1 ish compression. I've heard of endurance races being done at 250hp and "stock rebuilds" (head gasket and good machining) doing 300hp with appropriate bolt ons. Daihatsu were developing it when Group B crashed and then decided that a normal shopping trolley (G100 charade) was the appropriate place to put it.

But likeI said, rare. And so very 80s with large ports for the displacement and very low compression. I had one if those cars too. It had a bigger turbo and I would go WRX hunting with it