The Milltek system sounds good reading the above, specifically because the flange allows the natural progression onto a better downpipe and manifold with no cutting and welding of the system. If you truly intend to follow this route and develop a downpipe, then a little more info about the system on courtneys site might win a few more customers. If id have known a little more about the milltek system earlier, I may have opted for one instead.
As it is, I’m getting a custom system this Monday at Blueflame, which isn’t a cheaper option, but I do get to chose from a wider range of exit trims and specifically how quiet I want it to sound whilst still releasing some power. Which leads me onto Ffoegs point.
I think what Ffoeg is getting at, is that milltek and most exhaust manufacturers would like you to believe that they have "developed" and "tuned" there system specifically for your engine and model, sometimes on a rolling road, to release as much potential as possible and hence the price tag. If this is right, then fitting an exhaust made for the two litre turbo to a Naturally Aspirated engine is hardly what I call tuned and developed. The resonator chambers which cancel out noise waves generated at frequencies and amplitudes unique to the engine type by bouncing them back on themselves have to be accurately sized. Also, the bore itself should be carefully selected because gas speed is critical, too much gas speed indicates that that the system may be too restrictive hurting top end power, while too little gas speed tends to make the power curve excessively 'peaky' hurting low end torque. Larger diameter tubes allow the gases to expand; this cools the gases, slowing down both the gases and the waves and hurting power. It’s a fine balancing act and one you’d like to think was perfected by the years of experience these company’s have and not taking one system and chucking it on another model just becouse it will fit with an adaptor.
For me, I suspect a minimum of tuning actually takes place and that the system designs are created from an educated guess. Most of the power gains you see are a result of removing the mufflers where the gasses have to pass from one perforated tube across a form of wadding or wire wool and into another perforated tube which is very restrictive. Whereas Resonators allow the gasses to pass straight through and still absorb a good portion of the noise. Some gains will obviously come from an increase in exhaust diameter, but as talked about above, you can go too far. I'm not saying the miltek system isnt any good, quite the contary, its probably just as good as any other system you can buy for the 2.2 as not many places will bother to develop an exhaust for such a low key engine, and I like the fact that it will be easily upgradable. On the other hand, I bet I can see similar performance increases from a good custom system.
The biggest desission for me now, is what diameter to go with? I'm not sure weather to go with two and a half inch, which is good for 300hp turbos, or two and a quarter inch which I've been told is good for 250hp which my car will never reach, and keep the exhaus gasses flowing quickly? Any ideas???