Id have to agree about a better exhaust system improving the fuel economy on the ecotec, a single 2 1/4 inch system with pacemaker extractors will give noticable improvement in economy.The two most noticeable things that I noticed after fitting the pacemakers and exhaust system was that the engine ran cooler,one mark cooler on the temp gauge,and the fuel economy was noticably better than it was before,it slightly killed the bottom end power a bit though,but definitely increased the top end power delivery..I got a single 2 1/2 inch system at the time,it is slightly too big for the V6 and kills some of its low end torque,so Id go for a 2 1/4 instead of the 2 1/2 system.I know a guy who has the 2 1/4 system with pacies and it doesnt seem to kill the bottom end power quite as much,that size exhaust really seems to suit the V6 actually.Id actually be interested to see how much top end power would be lost, and how much more bottom end would be gained by running a single 2 inch system with pacies and a good free flowing muffler..