I have 40 series Flows on my truck, and i love them. They are deep, throaty, and overally agressive. I didn't notice too much of a difference between the 2.5" exhause and the flows, then i did when i had 2" and short glasspacks. I might have picked up 10 horsepower, but i didn't get the exhaust system to go that much faster. I got it to sound cool

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