^^^What he said. The whole point of a "performance" air intake is to pull low restriction, cold air into the engine. Cold air is more dense, therefore you get a bit more power. Air under the hood is hot, mainly because of that big hunk of aluminum that makes all the noise. Drawing in the hot air from the engine bay not only robs you of power, it also makes your engine more prone to knock (if you're trying to drive the wheels off it) by bringing in a hotter air charge. Mainly with a cone filter you get more noise, and to many people noise = power, so
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Back on topic, with the Flatt replica being solidly welded/bolted together, is there any concern about stress on the system from the engine twisting under load? The stock exhaust has the sprung flanges into and out of the main cat, giving it some room to flex. I know our engines aren't exactly jumping around the engine bay, but would you be concerned about long term problems? Stress cracking at the welds, etc?