I know that I said I wouldn't tinker with it any more, huh, it's never stoped me before.
i just bought a set of drill bits http://www.ebay.co.uk/itm/3-Piece-SD...item3f139d418a
£10.94 including postage, but i'm sure they'd be cheaper at a car boot sale. Quality is not relevant here !
When they arrive I'll run the 1 inch/25mm drill through the core. They're 450mm so should reach all the way through in one go with some of the chuck in the exit pipe too. 600mm would be more than enough.
I'm only doing it to satisfy myself that I haven't fluked a particularly optimum flow rate.
I was reading some older posts on different threads about owners feeling increased power from fitting a sports exhaust which flows much more freely. There is more to a good exhaust than simply gas flow rates, but generally performance and flow go hand in hand.
Once fitted, the owners with the sports exhausts declare an improvement and funnily enough nobody shouts "you have to get it remaped or the turbo will go squiffy because of reduced backpressure"...they just enjoy their gains. And quite right too.
I think drilling through the dpf still leaves significant restrictions in the exhaust for there to be no issue regarding turbo control. Between the front CAT, the second CAT and the standard super quiet exhaust there are still plenty of restrictions to present the turbo with a lot of backpressure. So that's what I'm going to test.
A few 1" holes to open the dpf right up should produce the definitive answers !
Whats the worst that can happen, can I really lower the backpressure very far below that of a similar car with a new dpf and a free flowing sports exhaust ?