Sorry James, I didn't mean to be abrupt, I just didn't want to beat around the bush with this, especially following a few comments in this thread. Neil provided the theoretical basis, me and Mark knuckled down and now it's done. It works beautifully. Hasn't trashed it on the track yet, but gave it a good run up the hill visiting rev limiter quite a bit (ZZR and wet road - oh dear!!, but softening the rear definitely helped with the grip) and the temp has been sitting around 80'C. More after Anglesey - I hope I'll manage to get the new gauges installed by then. rear water outlet at the back of the head with the knee on the bottom with new gasket: £100 brand new from X-Power engines - Piero is a great guy, but the current one on the engine can be modified as there is a 16mm plug that can be pushed out and replaced with 90 degree knee that is an OEM Ford part and costs about £15 on EBay thermostat housing - current part can be modified - haven't got the cost of the work yet. In order to keep things fully reversible, me and Mark have decided to outsource as a spare part (thanks goes to Chris at Red Line Components). The mods are: weld on on the stat face and blanking off cold permanent bypass from the rad, second hole and tapping the second thread on the stat face to properly fix the stat in two places, drill and weld on the additional tube above the rad return coming from the front of the car pointing backwards - this is the permanent flow circuit to connect header tank +/- heater. plus new gasket - £6 OEM Ford part. I've changed the stat as well, but not necessary. bypass hose - Ford OEM part - give or take £20. comes with clips the bottom hose from the header tank can be re-used, it just needs re-routing as the original space is taken by the bypass hose. Z bracket under the plenum chamber tensioning the throttle cable needs modifying (cutting off one corner) and mounting on the top of the brace rather than the bottom in order to create more space - costs just your time. I've changed the plenum to head gasket as I hate reusing them. Bravery of doing something most people are skeptical about.