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2.5" through the muffler would probably generate a less droney note.

I would steer clear of Flowmasters. They're not good at muffling and they're not good at performance. A Dynomax Super Turbo would probably do a better job of both.
 

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"Back pressure" is a huge mis-conception.. and is commonly misunderstood.
It is not desirable anywhere in the system.
This is correct. Backpressure is always the enemy of power. Engines do not need backpressure at all.

The larger the pipe, the more flow potential. But if your engine is not using that flow potential, then the pulses are moving slower and scavenging is reduced or lost. At the same time, the larger pipes tend to produce a more bassy droney tone that can be annoying. The larger the pipe gets, the more it appears to the engine like open air, i.e. the end of the exhaust system.

What your engine wants for power is header primaries of a certain matched length and diameter flowing into a smooth collector with a tailpipe of a certain length and diameter, probably not longer than 3' behind the collector. That's it. Anything tacked on to the end is potentially robbing power. How much we let it rob is a function of how quiet we want the system to be, where we want the exhaust to exit the undercarriage, and what emissions laws require us to do.
 

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One thing I did not quite get from all the tech talk ...... and forgive me if it all went over my head a bit, but a stock 4.3 in my van.... that would NOT benefit from a full 3" exhaust right? A 2.5" pipe after the muffler should suffice?
Not only would it not benefit, but you stand to lose power if any change happens. A 2.5" single system is more than enough for your van. And the smaller the tube, the less bassy drone to make you hate driving. And believe me: that drone is going to peak at whatever RPM you spend the most time at. It's the law somehow.

David Vizard's rule is 2.3CFM per open header HP. If you have a dual system, that's 2.3CFM per open header HP per bank. CFM numbers can be hard to find on mufflers, but Dynomax publishes them. A 2.5" Super Turbo definitely meets that figure for a single exhaust. Dual doesn't even need 2". You have a 190HP engine. It doesn't need that much, and it can't use any more.
 

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I'm running dual Magnaflows on my 92 350-V8... they are fantastic.
Yes they sound great too... deep powerful rumble at idle, no cruise drone whatsoever.
My 2000 V6 however, still happily running the big quiet stock muffler... no intention of changing.
I have used them on numerous VW/Audi turbo builds. On a turbo four cylinder, a single Magnaflow reduced noise to a nearly stock level (with no cat.) The turbocharger also does a lot to kill exhaust noise. On an NA engine, they would produce a nice, throaty roar with, as you said, no drone. They are sweet mufflers. If my wife understood the hobby, I would use them on my van too. But she doesn't, so I'm not.
 
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