Those Dynomax Super Turbos are good as long as you don't mind losing a bunch of power compared to a straight through style muffler. Switched my dad's road runner (480-500 hp 440 six pack) from a pair of 3" Ultra Flows to 3" Super Turbos and was immediately disappointed by a very noticeable seat of the pants power loss.
CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax
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