Secret of quiet dual exhaust?

So one thing that I really must correct on the GreenMachine is its too-loud exhaust. The P.O. ran a 2" system, with no H-pipe, to a pair of small turbo mufflers, with exit pipes out the side behind each rear wheel. Doesn't seem overly large to me, but I don't know what the stock size was on these. It is quiet at speed, but you really hear those pipes on start-up, and just idling through the neighborhood.

Took it to an exhaust shop to see about adding some quieter mufflers, and the guy warned me it wasn't going to make much of a difference, due to the diameter of the pipes and the available room. He was right, the new mufflers are still too loud, although better than before.

Rather than chase this thing with a bunch of expensive experimentation, I'd like to get some feedback on what people have that they know will work:

1) Is 2" simply too big for quiet? Engine is a 390.
2) Someone suggested turn-down tips, thoughts on that?
3) Would a 'stock' dual exhaust system have included separate resonators?
4) Does an H-pipe make a difference in noise levels?

I'd rather not go back to a single exhaust if I can help it, because the free breathing is going to help for towing. Am I asking too much? I don't need the GreenMachine to have a muscle car rumble.

 

My dad and I built up a 392 CID Hemi with dual carbs and over 700 HP, for his street use (I was the ripe old age of 22 back then). We installed it in a 1965 Dodge Convertible. The car was long enough and only 1 inch higher than stock. We used 2-1/4 inch pipe, with a resonator and a stock muffler on EACH side. It barely rumbled. You could drive with the radio at normal volumes, even at 'freeway-PLUS' speeds. Mind you, we used a lot of sound-deadening on the floor and trunk, and firewall.

I'd try to find some exhaust specs on a 390 or 427-powered Lincoln with dual exhaust, and see if you can adapt a similar system. Maybe one of the 2-door Mark IV models?

 

My thoughts also Stormin' Norman. Spend a little time with the books at your favorite auto partz store. My think iz that 2" pipes behind a 390 are way too small. I'd be leaning more toward 2 1/4" or 2 1/2" and you should be happy without an "H" pipe or an "X" pipe. BTW Straight out the back is alwayz more quiet then out the side. My 2 1/2s exit in front of the drive wheels and the AM+ XM+ AM+FM+CD+CASSETTE ARE ALL WORTHLESS, BUT GAWD I LOVE THAT RUMBLE

 

So your thought is that side-exits are a big part of the problem. Any ideas where I can find specs on a 'factory' setup? As simple as a visit to NAPA?

 

What mufflers were on there and which mufflers did you have installed? I can't imagine a car that size has limitations to muffler size.

 

My '88 Colony Park (5.0/302") had what looked like a stock dual exhaust (it wasn't)and you could BARELY hear it at idle, and a bit more but still quiet at WOT. Silent at any cruise speed.
The previous owner installed 2" stainless steel pipes, no H or X, and what looked like two fairly long oval shaped mufflers under the passenger seat area.
The pipes exited just behind the rear wheels.
(Sorry I don't have pictures.)
Since most people want to hear their dual exhausts, maybe the shop wasn't clear about what you wanted.
Maybe your shop used turbo mufflers or the cheapest replacement mufflers they could find.
Factory station wagon exhausts always exit on the side, either behind the wheels or ahead of the rear bumper.
Straight out the back exhausts will cause carbon monoxide to fill the dead air space at the rear of a wagon, and possibly (especially on an old car) be sucked into the interior.
Don't do that.

 

I've given that some thought, and I think the difference there is cats. Every car I've had in the last 20 years has had cats installed, so my frame of reference is a little skewed as to what things should sound like. The shop knew exactly what I wanted, but in front of the axle the space only allowed for about 16" of muffler....which leads me to wonder about available space behind the axle. Lots of room in a wagon, yes, but also a cargo well and a gas tank.

Thinking back to my old Starfire, that car had factory duals AND resonators behind a 425, plus they exited out the back.

 

Yes, My Mercury did have dual cats.
And I think the mufflers were 24" long.
How about this:
See if you can install a couple of smaller mufflers or resonators behind the rear axle, and have the exhaust exit on the sides just ahead of the rear bumper?
There is plenty of room there on a Ford.....
IIRC, some Fords were built with big round mufflers back there in the '60s.
I don't know when that changed.

 

Honestly, I would go to another mufler shop! Unless I'm mising some thing here, the shop should have...... you should be posting success not questions. Phone around for a shop that has some old timers, ask for old school boys and don't be afraid to say another shop does not know.

 

Well the shop did exactly what I asked them to, and they are an old-school shop with good-ol-boys running it. Just maybe a little short in the advise department. Since I wasn't thinking about resonators, didn't think to ask.

 

^^^

 

Smaller pipe is quieter, the 2" should be just fine for noise. H pipes/X pipes tend to quiet things down as well. Stock type mufflers should be used, not turbo or hi flow type mufflers. Resonators will help hush things a bit as well. Exits out back that aim towards the ground would keep it quieter too.

Try this place, not cheap, but nice stuff, and nice people. Oddball older car exhaust systems, stock custom, they do it all.
http://waldronexhaust.com/cart/index.php?main_page=product_info&cPath=61_40_94&products_id=4037

Mike

 

X2 on Waldron's. They did the S.S. pipes on the Batwagon. I think the old man is retired now but the quality of the work is the same, Jer

 

I feel your pain.... My parts wag has stailess Flowmasters on it, yeah it sounds great but no f'n way I'm into that BLAAAAA..... for a dialy driver, so for now my 83 stays single exhaust. A few years back some of us befiended a old guy who had just inherited his fathers car, bout new, nothing fancy 66 Plymouth I 4 door, with a 318. The car was 99% mint but the exhaust was starting to go. He as gona just sigle exhaust it but we talked him into duals. I was there when another friend phoned the exhaust shop for the old man.... he told him whats what and said.... "The old guy wants dual, but he wants it quiet, real quiet" It was that eazy, not only was the car quiet, it did have a very soft nice rumble, a "ya can have a normal volume convertation rumble"

 

My 73 Ford had 40 series Flowmasters on it when I bought it. It was too loud for my taste. I did a H-Pipe and a couple of stock type mufflers. Which toned it down quite a lot. Later on we took two glasspacks and reversed them before the mufflers on that really quieted the car down. It still sounds good with no drop in performance..