The new A1 boilers will not be the same as those originally built and are now so far removed from diagram 118 that they are given a new diagram code 118B. And the Trust may yet develop the design further in the future depending on what they experience during operational life. Boiler pressure is a part of the design process, a variable that you make use of within the limits that you understand and can design and construct within. If the repair costs of the Bulleid Pacific boilers working at 280 psi were less than those of the boiler fitted to the A1 then it would come as no great surprise. Steel boilers and fireboxes working at a higher pressure had been in use elsewhere in the world for some time, the designers involved must have been some peculiar fetishists, or maybe they were in a better situation than UK designers, or maybe it was a very bad idea because it wasn't done here or couldn't be made to work here and therefore these designers were very much mistaken and should have realised the error of their ways. The USA had the Flannery Bolt Company, the French developed a very good water treatment system and as a result closed many boiler repair facilities. Post war material shortages were a problem but perhaps the Bulleid engines were a little too much for the conservative BR. An adherence to an limit of 250psi was then, it was out of step with the state of development elsewhere, but this is now. The A1/P2 team are not limited to the BR way of thinking. The engines are being built not as strict replicas but as the next in the series making best use of what is available now not what was available 60 and more years ago. Piston valve diameter is one thing and port area is another. Today the diameter is not the same issue that it was because new refinements allow for a 9" design to behave as one substantially larger. So the proposed Super A4 would not present any problems in this area. But this is just considering a possibility on a wish list. The P2 and the V4 will be far more useful for today. There appears to be a behind the scenes drive to get the 2-6-2 done sooner rather than later. 240P15 is right, these people do not hang around or let the grass grow.