Look up ATSpeeds 106, that is about 400 odd bhp and running a standard inlet. not sure if he's done anything to it mind.
Tam also ran a standard inlet on his AX and that was about 240bhp at the wheels iirc.
Plenty others running standard inlets aswell. Just turn it up and see what it takes - you can get them for £25 so what does it matter if it pops! buy another, simples.
thats what i'll be doing anyway, running 1/2 a bar no probs will be putting 1.5 bar through it.