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Thanks,
It's a necessity if you want to run the exhaust back to the rear and actually drive the car.
Manifolds of engine are hottest, exhaust cools as it moves along the tubes, turbine, and then out.
downpipe runs towards the rear and it passes the engine manifolds, which can re-heat the downpipe (if there is no shielding).
This causes the exhaust gas in the downpipe to re-expand, slows exhaust flow, puts backpressure on the turbine, which of course slows down and creates a situation where the exhaust is very hot and high pressure on both sides of the turbine. Which doesn't make it or the engine happy. It can lead to variety of issues, but mainly it is a performance limiting effect.
By keeping the downpipe away from the hot manifolds, it can remain cooling which keeps the exhaust gas inside it from re-expanding, allowing it to continue to condense (shrink in volume) as it moves towards the exit, which helps create a vacuum effect in the exhaust tubes after the turbine (like a condensation tower in a nuclear power plant, same idea)
I see lots of cars with all manner of engine swaps and turbocharging, with downpipes that run right next to key engine components, or the engine itself, with no shielding. I can only imagine they run well for about an hour. Long enough to make a dyno pass, drive around a bit, but you can't really drive it much more than that without risking several issues.
Insulation is only part of the equation. Usually need some form of reflective surface to continually reject heat, which insulation by itself does not do.
I spent alot of time keeping the heat off the engine, and off the car, so I could drive anywhere all the time. In the rain or sun. Splash into puddles. Normal car stuff.
Eventually I want to further improve some areas to make the car drive through higher (tire height) waters as well. A water trap for the air filter for example. Maybe an alternative filter tube for hurricane days that pulls air from over the hood, like a Jeep.
I just get bored and start thinking of things to do...
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