A friend took his C-5 with a P1SC to a new Dyno shop in town , but only after he had a problem. He was making 9psi of boost on the stock((but super low mileage) ls-1. It ran great with a 3.90 gear & 3500 converter when he broke a belt. The car got hot,in fact he says it was 7 miles to town& he made it by cooling the car ,running & coasting several times until he got home. The shop put on a new belt & leaked down the motor. It only had 1% on 7 cyl & 4% on 1. No blown gasket etc. It had no timing & that's how he ended up at the "Dyno" shop. It also had no boost,3 psi at 6000. For about an hour after the Dyno tune it blew the blackest ex. smoke in the world,like a burning tire. It stopped in about 45 min. & did not come back. Since then he has installed headers with SS cats, Installed 3 in mid pipes,installed new MAF,Installed new throttle body & still way down on power. The cat-back is still stock. It runs ok (rough idle) but even with a smaller pulley still only gets about 4 psi. He even ordered a mail order tune on a new pcm,no help. Could the mufflers be clogged with the burned cat contents? Any suggestions would be appreciated. The guy is about to sell the car & that would be a shame.