We have to start somewhere...
Exhaust diameter:
Measuring the exhaust diameters of the 2015 cars. As last year, the method is to pick pictures approximately from behind where the perspective effects are limited. In particular I am (mostly) taking pics where the apparent front tire track width is smaller by half a rear tire or less. And then I count the exhaust diameter in pixels and compare it with the bolt to bolt distance in the light in the rear crash structure, which I measured to be 71.8mm last year. The exhaust pipe diameter, being slightly further away from the camera than the light, will be underestimated, but not by much.
Pics and results:
Mercedes engines:
Mercedes: 98.1mm http://i.imgur.com/z5QUHi1.jpg
Williams: 99.6 mm http://www.f1fanatic.co.uk/wp-content/u ... t-mald.jpg
Force India:
Lotus: 93.9 mm http://www.f1fanatic.co.uk/wp-content/u ... nasr-7.jpg (Not the best picture, a shiny right edge suggests at least a couple of pixels more, which would make the diameter close to 98mm).
Ferrari engines:
Ferrari: 98.6 mm http://formula1.com/wi/enlarge/sutton/2 ... 1fe589.jpg
Sauber: 99.0 mm http://www.f1fanatic.co.uk/wp-content/u ... asr-10.jpg
Renault engines:
Red Bull: 95.7 mm http://images.adrivo.com/images/950/q_8 ... 646132.jpg
Toro Rosso: 101.2 mm http://i.imgur.com/2sBTRkV.jpg
Honda engine:
McLaren: 99.3 mm http://images.adrivo.com/images/950/q_8 ... 646506.jpg
The minimum diameter allowed is 97.72mm (7500mm2). I am measuring from shiny pixel to shiny pixel, which would mean measuring something larger than the internal diameter, which likely is what the rules mean.
Overall, and accounting for likely measuring errors, they all seem to be running the smallest exhaust pipe allowed by the rules. Red Bull and Toro Rosso are difficult to measure, I'll update when better pictures surface and if they suggest anything other than minimum diameter, but the average of their measurements is bang-on on every one elses'.
For comparison, last years' Ferrari was running a much larger diameter, about 25% larger http://www.f1technical.net/forum/viewto ... 80#p533980
Edit: 97.9 mm for the Toro Rossos: http://4.bp.blogspot.com/-HjCWTJvxg9I/V ... 3fe134.jpg