Mine has no centre box and next to no back box and at the last MOT the teaster said it had to be be no loud than a comparable car and as he didn't have another Silvia to teast it against it passed, so it is up to the individual teaster and weather he's in a good mood or not.

That's cool then. I'll just make sure that I take it to the right place when I have it test. There's a couple of sensible testers round my way so fingers crossed it'll be alright! :D