TIME FOR AN UPDATE EVERYONE.
I have obtained a pair of silencers from a 2.2 and cut the top off to have a look inside.
There are three sections to the back box. The exhaust flows from the engine into section “A” through the holes drilled in the end of the sealed tube. It then has to pass through around 40 2mm dia holes into section “B” where it has to go in the pipe marked with a green arrow and do a U turn before going out the back.
In the 2 two boxes I cut open, most of 2mm holes were blocked with carbon or soot restricting flow. Section “C” is full of fibreglass and is designed to reduce the pressure wave created when each engine exhaust valve opens. You can see the small holes in the inlet and outlet pipe. I removed the fibreglass so you could see these pipes; it was completely blocked and therefore was not allowing exhaust gas to flow into the fibreglass or across from one to the other.
All these blockages will increase back pressure suffocating the engine particularly at low revs.
The 14mm hole that I have suggested you drill is marked with the red line and this allows the high pressure build up in section “A” to be directly released into the outlet pipe without having to pass through the blocked holes and that’s why the 14mm hole removes the hesitation as it removes the pressure build up. When the engine is revving, the 14mm hole is not large enough for all the gas to pass through so it follows around the normal route.
That picture you posted is certainly interesting. Having driven my Mum's 2.2 for the first time (ssshhhh, I didn't tell her!
) since my parents bought it, new, in 2006 I did find the engine response to be poor or being blunt, appalling. It’s no wonder she struggles with it!
Essentially what you’re saying is the back pressure in the rear boxes is causing the hesitancy issues. Presumably the 159 suffers to a lesser degree? The design of those boxes does look like it’s very restrictive.
I would suspect, with the brera being developed from a concept car and the exhaust outlet design being a key feature, that the exhaust itself has been compromised by the car’s design. They haven’t started with a clean sheet of paper – they’ve started with a design and have had to make compromises to meet with emission and noise regs that have been dictated by it’s lack of space in the back end.
I note that people are having mixed results too, after drilling holes in the box but even this solution seems to be a total compromise at best. – It’s hardly free flowing.
Surely the solution would be a standard free flow design back box?
But I suspect this would be unbearably loud give the level of deadening in the standard design.
So, perhaps a redesigned centre silencer – I presume they have one, could be provided to keep noise levels down?
Is such a system available?