If by "supersonic" you mean REALLY noisy... I can confirm mine is from about 75mph upwards....  (By 100 mph it's REALLY REALLY noisy)

Like i said. It's the French. 

You've just said you don't know and then the slander my suggestion. Go on, prove I'm wrong!  No and you're welcome to that one. However... without such a model I would suggest that without changing the silhouette of the Vitesse completely your best approach would be to try and modify the airflow round all the corners to minimise turbulence on that slab like front end. That would mean fitting boundary layer splitters on the verticals at the bonnet and windscreen pillars. Basically like those 'wings' you sometimes see on the front corners of lorries. Get the air moving smothly round these and it will tend to straighten out and draw off the turbulent air trapped across the front and round to the side of the car. And following on from the Vitesse estate rear radiators if you can duct as much hot air from the front of the car into that dead air space behind it that will also reduce drag. At higher speed/hotter temps you may even get a little extra push. It's what F1 does these days. If you could get the Vitesse supersonic you would even be able to use inlet pressure recovery to provide thrust. Concorde got something like 60% of it's thrust at Mach 2 due to the pressure recovery in the inlet duct to the engines where the air velocity was reduced to the subsonic speed necessary for a jet engine.

And now for something COMPLETELY different.     We're a few days after the Twelfth Day of Christmas, but still, 'tis the Season to be Jolly, and no one is more jolly, sometimes to excess, than Giles Brandreth.   For it was he who set up a fund raising evening last year in aid of the Orange Tree Theatre in Richmond. Surrey.   So far, so so, but he assembled a stellar cast of British actors, to talk about Shakespeare's Twelfth Night.   Actors in their anecdotage may not be your thing, but I think they are funny, and moving.  And, be prepared to be moved beyond measure, again, by Judi Dench! Clear the stage!  

Thank you, BT!    And, of course, I can speak of the aero of the Estate, although only subjectively. Like you (?) I thought that the low pressure behind an estate tailgate would optimise extraction, so when I built the Silverback, which was an exercise in Amateur aero, I put an enormous radiator right across the back, just in front of the tailgate:        Two enormous extractor fans (from a lorry) and intakes just behind the rear wheel arches.     But would it flow, would it heck!    I battled with overheating, despite a Davis Craig water pump, until I found out about internal flow, and ducted the intakes to the rad, which improved things, but not completely.   All this stopped me adding all the other things I wanted, a front air dam/spoiler, flat floor and side skirts, that would, of course, have given me downforce!   Eventually, after a hose came off in the passenger footwell - fortunately on the cool side as I had a passenger! - I gave up.   There is a reason why most cars have the radiator at the front! John  

That would have been good if only he didn't speak  rubbish.   Roger

Spot on. Exhaust exiting into the 'dead' air immediately behind the car helps re-energise it a little. Like having a little ephemeral camm tail on the back. Meanwhile having it exit into the smooth fast air (that's hopefully not turbulent at all) rushing along the side of the car just messes that up. @JohnD I was thinking about aero for the Vitesse a while back. I've made quite a natty set of graphs that show acceleration throughout the gears (accounting for gearing, weight, drag, and the tiny little bit of rolling resistance). They're not the easiest to interpret, but you effectively run along the topmost line (1st) until you reach the end, then drop down to the next line of the same colour as you change gear into 2nd (and so on and so forth). Here's one that compares a Vitesse to a GT6 with the same engine: You can see a bit of a gap in acceleration in 1st, which is mostly caused by the additional weight of a Vitesse. However, you can see that as you get faster the lines start diverging further and further. That's the effect of the brick-like aerodynamics. Because the Vitesse is so bad (though admittedly the Cd is an estimation), it seems like any improvement in aero would have quite a decent effect. The challenge is knowing what to do! And what's permissible within your racing class, of course. I suppose if you wanted to get technical about it you could make a DIY water tunnel  and buy a 1:43 model vitesse so you can do some flow visualisation of different aero modifications. I wonder if the estate has better aero...

IMHO, the flow along the valance is grossly turbulent, from underflow and the front wheel vortex.  Adding exhaust outflow won't make a ha'porth of difference. But I'd love to be shown I'm wrong!  Has anyone modelled a Vitesse into a CFD model?

I'd agree with that...but I'd quite happily settle for our deterrent being shared with a country of equal power rather than with one that has such an obvious power imbalance.