[xracerbob]

The burning plastic smell is quite different than the telltale clutch/brake smell. I would guess that it is exhaust related, as sustained throttle will put more heat into the exhaust system. I would check the speedo cable which seems to run pretty close to the exhaust first, then look for any wiring that may be close to hot items in the exhaust system.

The other thought is that if a clutch is going to slip, it is usually first going to do so in top gear. This should be fairly easy to detect- revs go up, car goesn't accelerate.

One other thought is with undercar exhaust could the carpet adhesive be emitting the smell into the cockpit? Is any part of the floor or tunnel warm?