[TheRodDoc]

The best method would be to cover all exhaust to the back of car with ceramic fiber blankets. They have to be custom made to fit each part of system. These consist of the blanket with a woven covering on the outside of them for protection and to hold them together. From heads to toward back of tail pipe.

Then spray a ceramic coating on all sheet metal on heat side of firewall and tunnel. No insulation where your putting it. Then a blanket insulation covering interior.

We have diesel engines in our streamliner that are producing so much horsepower that we have melted inconel exhaust headers, pistons and the whole tops of some of the valves. The painted body is less then a inch from the headers and turbos, 4 of them producing 100# boost for each engine. We use the highest temp ceramic blankets available around everything. They contain all the high heat and send it out the tail of exhaust pipe. The paint on the body never even discolors. It Works.
We also use special ridged 1/4" thick ceramic sheets for some areas. I think this is a refractory insulation made for melting furnaces.

Don't use anything that can burn. We have had some fires in the streamliner when we melted the headers and it is amazing how fast the fire burns up things. In just 3 or 4 seconds most any thing burnable was gone. Even a section of the body.
(the blankets won't stand direct exhaust blast) The blankets won't burn but will just fall apart when heat retaining ability is passed.