Automotive engineering has them. Best way to get 4 three inch collectors is to buy a pair of 3" to 2.5 inch reducers...it comes with two 3" flanges with each reducer. The reducers are cheap. NAPA may have them too.
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if it's cheap & reliable, it ain't fast, if it's fast & cheap, it ain't reliable, if it's fast & reliable, it ain't cheap
