In what I've done to various V8's & the Cummins, its been lots cheaper to do it with various pieces. At least 2 of the muffler shops here have the straight thru 4", shorty type, resonators, along with the mandrel bent 4" pipe. They can't bend the 4" here, but have plenty of mandrel angles, already flared & plenty of straight 4" pieces.
I'm only doing the aluminized now. No more rust! One suggestion is to have them put yours up on the lift, & do an estimate from where the 3" straightens out, just past the turbo & replace the whole works with the 4". 2nd would be just to replace the muffler back with the 4" stuff.
The stock mufflers are made for 1 thing, to be quiet. A side effect is they make great governors. The one on my V10 was the best governor I ever replaced! In our case, restriction downstream of the turbo benefits in more ways, like lower EGT & faste spool up.
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