i just installed a thermal r&d classic exhaust system on my 99 si and so far im liking it. the exhaust note is very, very deep, doesnt give the mosquito/bee sound of many exhausts out there. as for gains, i dont notice any but it could be it gives power only on the high end. anyone else who has a thermal classic system care to give there thoughts. btw, its very FRECKING loud and i need some aspirin now to kill my headache 
