...is it Spring yet?

Collecting parts right now for beginning of the season projects. One of them is redoing the exhaust. Right now it's 2.5" off the collectors with manual dumps then all the way to the bumper. I forget what exact model Magnaflow mufflers they are, but they have SS body, 2.5" in/out and fiberglass packing. Same exhaust that was on the car when it was a 360, now it's a mild 512 based on a 400 block. Did a chassis dyno and lost 40whp going through the mufflers. It's enough of a restriction to where if I have the dumps open I have to load a different tune on my Holley Sniper or the thing will spit and sputter while it tries to relearn.

I would like to go with a 3" muffler with 2.5" tailpipes to try and keep the noise down. Any recommendations on what muffler to use? Would like to stay with SS. Looking around the net it's not easy finding flow and decibel comparisons.

Thanks.

Had 3" into Flowmasters on a 512" Duster, adding 2.5" tailpipes really cut the racket.
The Flowmasters aren't my go-to muffler but they were already on the car from a prior owner.
I've also had a 406" Duster, 2.5" with Flowmasters, 2.5" tailpipes and factory tips.
Same deal, mufflers already on the car.
Both cars had a nice crisp sound, no drone with the tailpipes.

Id consider magna flows, I love them, they are loud at 7k but id think your massive stroker is a semi low rpm monster.

LEAST I forget about the STACKED SYSTEM that Addison was famous for on the Silver Bullet ... with the 4 Caddy muffs ....

You could hear the ROAR out of that Hemi BUT THEN it was quiet enuff to heat the tires BARK on the gear changes.

DO IT with light TURBO muffs these days !

Lose the 2.5 inch pipes, they are a really big restrictor on BB motors Been there done that
Run 3.0 or bigger from the collectors to the end of your new system, I used a set of the early Magnaflow 3.0 side inlet with the 3.0 inch center outlet by 14 inch wide by 7 inch high by 16 inch ( I think, maybe they where 14 inch long) mounted at the rear bumpers on my old pump gas 400 stroker motor, that car picked up .02 ET and .2MPH in the 1/8 mile removing the complete exhaust system, 7.01 ET 95.5 MPH versus 6.99 ET with 95.7 MPH without the exhaust on the car. I think the difference was in the weight, not the exhaust restriction
With those mufflers mounted behind the rear end and exiting at the rear bumper it was fairly quiet while cruising and louder at WOT but not like trunning he car with headers only

MarkM, here's the flow and decibels comparison you are looking for.

Summit brand 3 inch stainless on my 65.Been on for at least 15 years.Still look new and sound great.Not loud and not quiet.Oh yeah they were cheaper than almost all aftermarket one.No seams also.Rocky

Use a 3" straight through style muffler. I prefer the Dynomax UltraFlow.
The Dynomax Super Turbos are real popular b/c they're pretty quiet, but they kill a lot of power.
The Hooker Aerochamber is nice also. A lil quieter than the Ultra Flow, but flows MUCH better than the Super Turbos.

Ordered a pair of 3" Dynoman Ultaflows. Thanks again Moparts!