I have a friend who used to run a 200+ HP 2.0 liter four-banger. Race motor only; he had something like ten grand into the heads, it ran on race gas, had no power at anything but very high revs, and needed constant attention. Went like stink, though.
I think he bumped the motor up to a 2.2, then a 2.4 liter. Again, race-only. He may very well have been making 250 HP by the end. He had problems keeping the motor together above 7000 RPM, though--he wound up putting a lot more money into it to get it to live decently at that RPM level.
I think there are one or two customers of Jake's (check the "aircooled technology" board over at
http://www.shoptalkforums.com ; they may post there) who have gotten "super hero" motors from him that run ~200 HP.
There certainly aren't many of them around, though!!
I recall that John Rogers' 2.8 liter four-banger made close to 200 HP, but tons of torque. Another race motor, another very stressed (and therefore somewhat fragile) beast.
Most of the competitive E-prod 914s are making 180 HP from their 1.8 liter motors. Again, race-only. I know some who claim to be getting 195 HP, at least until the heads start running too hot. I believe the 2.0 just got accepted into one of the Production classes in the past year or two, so we may see more 200+ HP race motors in the near future.
--DD