Agreed. I decatted my OEM downpipe and noticed nothing, other than a tinny blowing noise because the wall thickness of the cat carcass is so thin. As well as that, the way the OEM DP necks down to 2.5" abruptly isn't pleasant for flow.
I went for an APR downpipe, which is much thicker cast steel. Milltek offer something identical to that now, so obviously they found the same Chinese foundary and did a deal
The result of the cast elbow is a really refined tone. No nasty blowing type noises, just enhances the tone of the factory exaust really nicely, and improves flow no end being 3" ID all the way through to where it joins the factory exhaust.
An intake can liberate as much as 30hp at the top end at Stage 2+ levels, with no loss of bottom end......but you need to spend £450 on the VWR intake to get that kind of gain....and it fits like an arse. Rubs on things, knocks coolant elbows off etc. The Revo intake probably sees similar gains, but it's very noisy.
The factory airbox needs pressure testing ideally, just to see how much of a pressure drop there is. If it's less than 0.1 bar, I wouldn't worry about it personally.
