Simon, is your dino reading low or is the saw just junk?
Heck a good muffler mod should bring a 5.4 hp saw up to 7 hp, that would indicate that your only getting about 10% for those high priced mods.
I would say I am getting an easy 7.91 hp from my 359 mod. Anyway, how do you measure hp to 1/100th of a hp with a mechanical dyno, or is that just what your hack copy of desk top dyno prints out.
Crofters 372 EHP is close to my self-modified 066 which is outcuting stock 088's and 3120's and is placing with other modified 120cc saws. No dyno requred!
A good 372 should be closer to 10 hp to be worth talking about.