After some review and first pass dynomometer testing, there are some slight design changes. Air vent holes are opened up from 1/4" to 5/16". Counter-drills are enlarged to give more clearance to eliminate touch up of welds on the original air filter cannister. The 1/2" drill through holes are enlarged slightly to allow free fit over posts at assembly. Ramp angle was changed from 15d to 10d and the outer edge was thickened to accomodate the larger counter-drills. This new design has yet to be produced or tested (as of 14 Nov 2011), but we expect it will produce essentially the same results. This new drawing is labeled "Mark-II".

I ordered a pair of these in early Nov 2015, while I was traveling about. Initial shipping was quick, followed by a delay before I could arrange the relay shipping. I finally got possession of the parts Jan 20, 2015, but haven't gotten around to installation yet.

Design for these parts was drawn up and developed by Steve Gyles in the UK, following lots of input by multiple members of The MG Experience BBS. A few prototype parts were produced by Steve Ash in the UK followed by at east two limited production runs (with parts sold at cost). For all those asking how and where to procure these parts, contact Steve Ash in the UK at esselay.123 at btinternet.com

I got my stub stacks installed May 30, 2015 and gave them a good test run on the road and in some hills on June 1, 2015. They do seem to live up to expectations, and I suppose the reported 4-hp improvement may be real. The engine seems to pull a bit better towing the trailer in the hills. This is not a radical change, but another nice incremental improvement. It takes maybe one day to get used to it, after which the new performance becomes the norm. Looking back over decades of similar minor changes the accumulated overall affect is quite notable. Think change of 1500 to 1600 block, now 0.060" overbore, early 1800 cylinder head, stub stacks, 3.90:1 differential, slightly lighter flywheel, MGB clutch. I would not change it all back to OEM specifications.