Why bother. Just take the mufflers off and see what it sounds like. I drove around for 5 months last year with no mufflers.
Then I went catless, it got to loud, I put the stock mufflers back on and left the gaskets out. Car sounds great.
215,000miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. CHECK your oil, these cars use it.
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