81 turbo is correct. The addition of 3 mandrel bent downpipe and exhaust will add atleast 25 rear wheel horsepower to your car. This is provided you get away from chambered mufflers and use the straight thru kind. 3 should suffice if you do not plan on upgrading your turbo to some type of monster. You will decrease backpressure to the turbo, thereby increasing turbo spoolup. This also allows your motor to breath more easily. As far as letting the heat out of the turbo, that is not something that will help. Keeping the exhaust gases heated after leaving the engine is a plus. This helps to speed up the exhaust, contributing to spoolup and performance. This is why wrapping your downpipe and using turbo blanket is used in performance applications.