I know this is overkill, but I'll tell you anyway.
I have a nice 367 street engine that goes like the dickens. In 1999, I installed TTI headers on it, and dual 3" all-the-way pipes. Under the rear seat are the 3in/3out Dynomax 3pass mufflers. I am very pleased with this system,in every way. Not too loud, and no drone whatsoever, at my cruising rpm of 65=2240
Now I installed that system in 1999. And every winter 5 in a row, I swapped that 367 out for a stock low-compression 1973 318, and ran that for the winter, while I freshened up that bad-boy.
Well not quite stock; I did install a small-port 4bbl intake,an old Thermoquad, and some stiffer valvesprings.
Here's where it gets interesting; That 318 was the most awesome winter engine ever.
I ran it with 3 different transmissions and several different chunks. I think my favorite was the A998 with the wide ratios,and a 2800TC, and 3.55s. That had a starter gear of 2.74x3.55=9.73. Between that,and the 2800TC, that318 still remains one of my favorite all-time combos.
Here's my point.; Everybody ahead of me posted correct information, and I agree with it 100%.....................................but, I can tell you that a 318 running into that freeflowing exhaust went like stink!, with the combo I described above. And with the stiffer springs, she went 5500 easy, still pulling hard in lowgear.And when she hit second she jumped ahead,eager to keep going.
Here's the deal; 5500 is waaay past the power peak for a stock-camed 318. But that a998 has a bit wider ratios. So when I shifted it at say 5200, the Rs dropped to 2920, right about at the torque-peak,and so, that little engine that could, jumped to it.
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I have never had to run cats here in Manitoba, and will never voluntarily do so, And I know nothing about their propensity to drone, But assuming a cat by itself , doesn't drone........... I would run the biggest bad-boy pipes I could find, into the biggest bad-boy cats, mounted where the muffs usually go, and then I would run the second biggest pipes I could find, from there to the back, and then I would turn them down between 30 and 45* .That's what I would do.
And If I thought it was too loud, I would cut some pipe off near the back and swedge the remaining ends down to fit some resonators, and then send the exhaust out thru rectangular ends like the 340 cars had.
But if the cats did drone, I would move them forward and install anyold three-pass muffs in their vacated place.
That's what I would do.
Cuz I know how an old teener runs, when it ain't wheezing thru log manifolds, and into a pipe that is mathematically correct for it.And if you think a 230 rated cfm carb is limited to 230 cfm, well you have probably never installed one on a 340. And if you think a stock318 can only pull the rated cfm of a 230 carb, then ..... well I guess putting an 850rated carb on it was dead-wrong. But I'll tell ya, that stock long-block 1973 low-compression 318really sang.
Your results may vary,cuz I never ran cats,lol.
But if you have one of those 2.20 rears, or a 2.45 rear or even a 2.73 rear, then forgetabout it, it's hopeless. The engine hardly ever gets past 3500, and so basically it could breath thru a straw.At both ends hahaha. Sorry, I couldn't help myself. So for this application I would just put a resonator-tip on the end of the pipe, with a rectangular opening; those kindof burble.