Jerry said:5 more HP.
Not free, though
Many car companies cut corners to save money. I've built GM v6 engines that had stock tubular exhaust manifolds (in the case of Fieros) where they had just welded the short tubes over holes that were machine punched without removing the overlap. One more machining operation to match the flange to the short runner produces 8 bhp that GM left on the table to save a single easy solution for free power.
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