The objective of a Perrin downpipe blanket is to hold in heat. Inside the engine bay is an environment of extreme temperatures. A balance needs to be sustained. When too much warmth escapes from exhaust parts it causes inefficiency. A Perrin downpipe blanket is designed to keep heat locked inside the tubing so it does not radiate. This elicits a chain effect. As adequate temps are maintained, your components work at an optimal level. Exhaust gases flow freer and moreover, neighboring components are kept out of danger. For Subaru turbo models, a Perrin downpipe blanket can take away a lot of headaches.
You need exhaust gases to maintain a high temp in order for them to move faster. This is the main point of a downpipe thermal cover. It keeps exhaust airflow nice and warm without letting it seep through the tubing. Confining hot exhaust inside the pipe allows it to move with greater velocity. It can turn into a safety issue, as well. A downpipe thermal cover protects heat not only from influencing other parts, but it also stops it from creating an issue outside of the engine compartment. In the event a flange is fractured or there is a leak, it can stave off unpleasant symptoms such as fumes and high temps outside of the car.
The biggest factor why drivers prefer a downpipe thermal cover is function. Exhaust is kept at a higher temperature, thus, performance of the part improves. Since it is not a turbo upgrade, it is hard to pinpoint what kind of gains a downpipe thermal cover is responsible for. What it does more than anything is help other aftermarket exhaust accessories operate at a higher level. The reduction in radiant heat keeps air from exiting. Likewise, the downpipe heat blanket does not let the turbo become too hot. Silicate wool is the main ingredient why. This material is how the downpipe heat blanket is able to provide insulation to the surface of the pipe.
Installation is very easy. The downpipe heat blanket features mounted steel rivets that line the perimeter. A steel wire is how you will tightly lace it together around the tubing. There is no need to break out a wrench: You can put your WRX/STI downpipe blanket on without removing the pipe itself.