hiya mate. There is lots of debates about what to do. Large bore, small bore, straight through, tunned lengths, tunned bends, back pressure etc etc.
Being the 16V motor, its all about revs, and at high rpm, you have high gas flow, easpecially after the burnt fuel expands into huge amounts of gas. So it most important to just get them out asap!
however, back pressure is said to give torque is tunned properly. Now, its my thinking that as the exhaust gas leaves via the exhaust port, the fast moving gas creates an area a low pressure behind the valve. Whent he induction stroke starts, this helps as there is not only the decending piston creating a low pressure zone to suck in A/F mixture, but once at its lowest, thats it, no more suck can be created. But, the fast moving maixture has velocity, and keeps filling the cylinder with the piston rising, the low pressure behind the exhaust valve now helps with better cylinder filling, sure some is lost at low rpm and looses torque, but at least is a clean mixture with no burnt gasses from the previous burn. This also helps cool the cylinder, reduceing the chance of knock (second flame fromt cause by over heated carbon deposts or plue electrodes. So, if your running lots of overlap, high rpm needs, then the backpressure is not wanted.
FOr example, the pinot need lots of overlap to reach 100bhp/ltr, but the CVH need very little, especially the EFi engines.
In your case, i would try to get rid of tha stupid 90d degree bend under the driver seat, or cut the rest of the system short and exit the pipe under the passenders door (what im doing).
You wont beable to work on tunned lenths as power flow aint that good, and not many people fully understand the pulse tunning theory (unsing the energy in the created soundwaves, not of the combustion, but that created by the gas moving, and starts from the valve). But different length pipes creates different power curves, but there will always be one bad sport on a tunned engine, it all down to where you move it with the induction and exhaust system.
I wouldnt go above 2 1/4" bore, and thats still largeish. Remember to use mandrel bent pipes, weld them together But remove the weld inside the pipe)rather than clamp (as you have said), 1 or 2 competition silencers (better flow), ANd basically, commonsense.
