This does not have anything to do with loud or quiet mufflers. I have heard that running straight pipes on cold days was bad for the exhaust valves. Before the exhaust valve totally closed the piston was on a down stroke and would suck "cooler" air over the valve and the change in temperature "might" crack the valve. Any opinions? (Personally I like straight pipes at midnight for about 15 minutes. More than that and I get a headache.)
