Good work chap - really looking forward to hearing about the results. I actually think this WILL make a difference, but perhaps only when the horribly restrictive baffles are removed from the exhausts (or the Sport/Semi-Sport pipes are fitted, when the factory finally get round to releasing them again). Sports Cats on performance cars are huge and need a big surface area to work - both in terms of ceramic media and cross-sectional area. I had a 'sports 200cell' cat on my Spider (2 litre)and it was too restrictive overall, despite being way bigger than the M3W cats. But as we need them for the MoT test, I will be having a cat-replacement pipe made up for each side I think, so that it's not a one-way trip.
The 2 baffles in the exhaust are really very restrictive, with about 5 small holes drilled around the outer edge of each. The straight through Sports pipes will lose these for good, the semi-sports will retain baffles, but have bigger holes in them. I read into this as meaning the noise of straight-through might be too much for some, but I am sure performance will come with it. It is well known - and already said - that Harley engines like open pipes and a non-restrictive exhaust, but the stock M3W has just the opposite in my view, likely contributing to the glowing headers as the hot gases struggle to get out.
It will be very interesting to hear what the infamous Stage-1 tune brings - if it every materialises - but I bet that majors on exhaust revisions in one form or another. But in the absence of that, my preference right now would be for a pair of decat pipes and the semi-sports exhaust tailend....
