There is no need to go for 3" bore diameter. We have 430bhp cars running quite nicely on 2.75" and the smaller the bore the easier it is to keep quiet.
Different cars, different setups, different results, but… speaking to Randy at Hofmanns they had found bigger bore, slower gas flow, less dbs (if not lower tone)
Jim has the H2 silencers with the extra voids at each end, meant to cut a lot of noise.
Getting one for xmas to replace my larini ‘cannon sport’
There is no power to be gained with the 3" exhaust…I tested it out on the dyno…
Do you have a dyno in your bumfuck shed 
I bet you wish you did hey Frank, lol probably could have bought one twice over 
Man you got that right, I’ve spent enough dyno bucks to keep bumfuck in a lifetime supply of corn dogs…
Yes and so did I, took a lot of mapping to get the power back the car lost, overall I ended up with about a 2hp gain and that was at the top end.
oo, wot’s all this then?!
NOISE is a big issue now and for SC installs, you need a big silencer to help meet some db limits. Turbos are pussycats, I can keep a 260bhp Audi install quiet with a 6x18 silencer - on an SC that would be obnoxiously LOUD.
The first Exige S we had on the dyno gave 202bhp, so the std 8x22 was fine on noise. Things have moved on a bit since then. With recent re-flashes yielding anything up to 280bhp, you need to get creative with the noise-control.
The H2 with the 2 noise-cancelling chambers works very well. Ade with the 70mm bore will need a 3-chamber design, which I’m working on at the moment because some owners are approaching +350bhp now. The internals on that (H3?) are …challenging.
A silenced de-cat pipe helps a lot but our European customers need a catalyser. The 100cell design works extremely well power-wise, as good as a de-cat but unfortunately, just as loud.
New website coming soon, a whole page devoted to NOISE - how sad.