A common problem when tracking a Miata is heat radiating from the trans tunnel. This may not be a huge problem for daily driving but on track both the exhaust and transmission heats up the trans tunnel and makes it unbearable with the roof on. AC wont help since it is disengaged at WOT and here in Norway rules say windows must be fully closed on track.
My first attempt was to heat wrap my header all the way to the flange. That helped a a bit but the trans with it 80-100 C oil seems to be the main problem.
Insulating from the inside is not as effective as on the outside since the metal in the tunnel transfers heat to the surounding parts of the tub. Also there seems to be surprisingly little air moving above and on the sides of the trans since the tunnel is perfectly clean with no water/dust/oil marks at all.
While my car is on jackstands I'll try the same approach as what 949Racing did on their endurance car by applying Thermo Tec Adhesive Backed Heat Barrier as described in this thread on mt.net:
I didn't have the luxury of having a clean shell without the trans/engine/PPF on the car but managed to get the barrier on with some bad language. I covered the whole tunnel from side to side all the way to the turret.
I hope this helps as I just removed my AC :-/ I might add some additional heat barrier on the inside by the accelerator as this is closest to the exhaust.