Without any hard data to go on, I decided to see exactly what a stock K20A and K20A2 could stand up to RPM wise, and what would break first.
First the K20A2, this was out of a UK Civic Type R, it had dome some 5K miles before I got hold of it...
We ran it for just over 4 hours at between 8,250 and 8,750 RPM on 100% throttle, when this happend!
one of the inlet valves snapped off just below the collet, dropping the valve down the bore (in the pic, the head is just rested back on it's seat).
looking at the bit's that are left, there is no clear reason why the valve failed, the break is clean and it's not where we expected it to fail (was expecting the head to fall off or the like).
clearly it's made a mess of the piston and head, but that's the total extent of the damage.
The K20A was next up.
this was subjected to the same treatment, after 4 hours it was fine, so we increased the revs to 9,000, then 9,250, and kept going till...
this ultimatly went big time!
one piston has completely dissapeared (there are bit's of it all around the engine and spat out the inlet and exhaust), and the other was beeten into a ball of ali (placed ontop of another piston in the pic)
one of the rods has snapped, and the remaining bit punched out the side of the cylinder bore, also one of the valve heads has got pushed ou the side of the block by the crank.
this happend at ~9,700 (hard to be exact!) but at this point it had been running non-stop for some 6 hours at WOT.
clearly looking at what is left, they cannot stand these sorts of revs, below 9,000 it was OK, however, how much further before this happens is in the lap of the gods...
what you make of this is up to you, suffice to say that for a stock engine we are not going to be running them in a race car at over 8,600.