kunjeng is correct on the temperature volume and pressure relationship
in diesel engine you don't need a spark plug as the diesel will detonate on its own due to the pressure..
if you have water under high pressure it'll boil on itself
however I'm not sure if heat loss is going to affect the energy change much...the exhaust spends only a split second in the housing before going out and the housing and dump pipe would eventually gets close enough to the exhaust temperature under operation, so will the dump pipe...
maybe as the engine go from cold start there is a large temperature gradient across, however at constant operation I'd think the difference is hardly noticable
unless you kinda go hard acceleration and sudden slow down... and hard acceleration again...sorta cycle thing unless on track don't think will ever go into such extremities
with heat shield the temperature across will be higher.... without heat shield the temperature will be lower, gradient remains the same
I think the main key to turbo operation is the nozzle size, the inducer and exducer ratio, how small the size of the nozzle when exhaust come into the housing and how big the exducer is..and the exhaust to compressor ratio...
and with regards to the blanket cracking the housing, that will happen if you dissipate heat too fast...if you pour hot water into a glass, empty it and immediately put ice in it..the glass will crack, try it at home~~...so retaining the heat and slowly dissipating it will not cause the housing to crack...if temperature is too hot, it'll melt but I think housing are of course design for these temperatures..