When cosworth first made the 24v it had a standard 2.9 12v block, but with in year they had modded the block because were the main bearing caps met the block it would crack. The new block have webbing in them that helps a lote. To move up into the 600 to 800 bhp you need to rev the engine more and even causes to new blocks to crack.

6500 to 7000 max