I just can't see how you could make the intake and exhaust the same temperature, the explosion of petrol in air creates a lot of heat (as well as a huge change in volume - which drives the piston).

The heat is a by product of the chemical reaction.

The only efficient use of it in the car is I think to heat the air for the cabin heater.

The other good thing high temperature exhaust does is get the hell down the exhaust pipe faster, if you let exhaust cool down in the pipe is has more resistance to flow (some call backpressure). That's why there can actually be a case where an exhaust pipe is too big, exhaust slows down and cools in a bigger exhaust.

Hmm am I still on topic? I think so. I have a tendency to ramble...