The Swedes make crazy high power from redblocks.... but for drag racing. AFAIK the 500 BHP has been well passed by them.
Then again, the engine only has to work hard for 30 seconds in that application.
In 85-86, the Eggenberger and RAS Group A 240 turbos made about 360-or-so BHP with their B21E K-Jet engines with homologated parts on the AvGas of the period. Even so, a mid-race turbocharger change was factored in for the Spa 24 Hour races.
As we know, proper race engines are built with power in mind, not longevity or comfort. So clearances, etc, are way off factory spec, because the next scheduled teardown / inspection / rebuild is after the race.
300 BHP should be had reliably from an 8V; anything more? Of course, but IMHO, unreliably.
I hope to have my 16V B230 in the 142 up and running (finally! The budget is there!!) before the end of the year. I'll be very happy to get 350 BHP from it; I believe it will be capable of more, but I want to spend my time in it, not under it.
