Secret of quiet dual exhaust?

OK, I took some measurements:

Main pipes -- 2.25"
old mufflers -- 9"x14" nondescript 'turbo' mufflers
new mufflers -- 10"x18", probably Walker (it's what was on the shelf)
Over-axle pipes -- 2"
chrome tips -- 2.25" side exit

Looking under the back, there is no room for a muffler. All the space is devoted to gas tank and cargo well. Ahead of the axle it looks like there may be room on either side of the driveshaft for a slender resonator. Or, closer to the trans there could be room for a short muffler on each side, but it would have to be small like a cat.

Tomorrow I'll pay a visit to NAPA and look through their book.

 

If I get time tomorrow I can jack my wagon up and take some photos of the exhaust system in my 73 Ford..

 

mufflers

hi people my 67 390 country sedan has duals with no h-pipe and is very quiet i think you problem is the mufflers there are several grades of walker mufflers go to the parts store and ask for OE standards for your make and model single exhaust and buy 2 mufflers ?? just a sugestion

 

ok...Taz 's advice is the most solid so far....(sorry guys)

Green...the unfortunate part of the exhaust world is that everyone wants a 'lookatme' sound.....thus the 'bone stock' 5litre Mustang that goes by you slow....but it sounds like its doing warp speed....and you hear it coming for a mile

your car came stock with a 2.25" exhaust system....but it had 2 REAL mufflers on it !

Unfortunately companies like Walker and AP dont make the old stuff anymore
My 72 has the stock mufflers from a 1999 Mustang on it..and its amazing how nice they sound without Cat converters included !!

point is?....most new performance cars have decent mufflers on them...its the CATs that quiet them down.

otherwise...I personally dont care for all the Flowwhoever type mufflers...they all sounds kinda 'tincanny/echo chamber' to me

1) Is 2" simply too big for quiet? Engine is a 390.
no..the stocker was 2.25

2) someone suggested turn-down tips, thoughts on that?
no!..the 1st time you drive on dirt...you'll regret it...(think of the dust storm you'l create )

3)would a 'stock' dual exhaust system have included separate resonators?
...no...not till a few years later

4) Does an H-pipe make a difference in noise levels?
no...not really....all it does is equalize the exhaust pressure

 

First off, 2 inch are too small for a 390. My muffler guy uses 2 1/4 behind my 351. I would think that you would need either that or a 2 1/2 behind the big block. The determining factor is the scavenging. You want the right diameter for the pulses to assist one another. A few years ago, Hot Rod did an exhaust system comparison test. No cross over was a poor for horsepower as no exhaust. An "H" improved things noticeably, and an "X" improved things much further. The difference was something like 40 or 50 horsepower on the dyno, in their test. It also made a difference in the fuel economy. A 2 or 3 mpg gain is not to be sneezed at. The X will also make the system quieter. My 351M has Hooker long tube headers, the X, 2 FlowMaster DeltaFlow mufflers, and out the back. Before the X and with the stock manifolds, it was much louder than with the headers and the cross over. There is one other BIG advantage to the cross over. If you damage one muffler, it keeps your back pressure even. Having one side restricted by a damaged muffler is a great way to burn valves in a hurry.

 

I hope these pics will be of help. Notice the "reversed" glasspacks are in between the "H" pipe and the mufflers.

 

Great stuff, that helps a lot. So your glasspacks are where I was imagining some resonators could go. Pipes are 2.5" or 2.25"? They look thick. I've never heard of reversing a glasspack before, can you explain the theory? It has me curious. I also like how your pipes extend farther back, exiting just ahead of the rear bumper. Can you measure the length of your muffler for me?

Trip to NAPA was a bust. This is the good-old small town NAPA with the machine shop in back, the one you can trust for just about everything. Well, they didn't have any old exhaust books, and the only computer parts they can look up just show the most common options. Sad day. In my case, we had to look up a 4-door Galaxie 500, and it only listed a single exhaust. The specs on that were a 21" muffler, 2.5" in and 2.0" out.

 

The pipes are 2.25 inch. The mufflers are around 18 inches long. If you ever have looked inside a glasspack,they do have some baffling,and usually install one way. I had the mufflers on there before I went back and did the resonators and h-pipe so there was a big difference in how loud the wagon was. It still sound good at idle/low speeds, but it doesn't "drone" anymore...

 

So the glasspacks were an improvement over resonators, or vise-versa?

 

Mike and I are gonna go fistacuff some day...we either see things the same...or opposite.
as for what magazines say...they want to sell stuff...so....pashaw
I prefer to rely on my personal experiences.


Glass packs are a nice cheap version of a resonator

On Stovebolts 59...we put Red hots under the front floors...it was loud..
..so we put another pair under the back seat area..and reversed them as Hipster described....still hada real nice kackle...but waaay quieter !

most Glasspacks now come with a flow direction stamp..( in/out)
but they tell you to do it the LOUD way...(hey look at me theory)...

the inside of a pack has rows of louvers...if the flow goes over them...its loud..(its literally a 'straight pipe)....but with the flow going INTO the louvers...then its quieter...but will get louder as the fiberglass disintegrates

they are a cheap experiment

 

Depending on how much quieter you want your car these might do it for you. They are resonator tips from Thrush. I have a full 2.5" on my wagon with the exhaust exiting behind my rear tires and the did quiet the exhaust a noticeable amount and basically got rid of the drone at highway speeds.

 

Years ago, before x pipes and Flowmasters, I read a perf mag article on exhaust system theory, so some of this may be misremembered, but here goes.

Turbo mufflers were originally installed (one only) on turbo Corvairs. So it was a single muffler processing "noise" from a turbo-muffled (turbos can cut noise like cats) 6 cylinder engine. Back in the 60's it was said you could also get "Hemi" mufflers, which were very similar to the Turbos. So putting this "single muffler from a six" in pairs on an 8 made it a "single muffler on a four" which could (would) be louder due to the exhaust pulses half an 8 "speaks" at.

So, to quiet it a little...

The balance tube/crossover/"H-pipe" mates the 2 sides of the exhaust and allows the V8 exhaust to "speak" like an 8 (think how quiet really stock'y single exhaust V8 cars were) instead of 2 four-cylinder engines. Balances the exhaust pulses. Also is suppose to improve lowend torque.

Smaller exhaust tubing shouldn't cause noise, unless it is so small that your exhaust is speeding thru it as it is pushed out. Think about how a lowrider with pea-shooter tips sounds as the exhaust flow speed rockets out of the tips.

Factory exhaust systems (and aircleaner inlet snouts!) were sized for best flow and least noise. But even if pipes were 2-1/4 or 2-1/2 in diam, the diam thru the muffler(s) may have been 2" (restrictive, maybe quieter?). Also, just because a car had larger diam headpipes didn't mean it had large tailpipes. The exhaust cools as it goes thru the pipes and muffler, so it doesn't need the same flow area for the tails, allowing them to be smaller (restrictive, maybe quieter?).

Finally, I mentioned aircleaner inlet snouts. Open element is noisiest, but looking at late 69's early 70's V8 Chevy's it can be seen that even tho the basic "can" and filter (Fram CA326 I think) is the same from one engine size to the next size, the inlets got larger from 350" to 396-402" and larger still to 454", but still small enough to work with the correctly sized exhaust to keep the car quiet. Even with duals.

Try a simple weld in crossover (one diameter size smaller than your headpipes) and look for a genuine "quiet car" muffler from somehting like an older (mid 70's or earlier?) Caddy or Chrysler.

Good luck,
Tom

 

Rev: Whether or not Hot Rod made any money off the 'experiment', my experience with Nora is this: The first day I had Nora, I had the dual exhaust installed, with the FlowMaster DeltaFlow mufflers. It was quite loud. The exhaust guy warned me about that and said that the noise would drop noticeably once the cross over was installed. I held off on the cross over while I waited for the long tube headers to come in and be ceramic coated. At the same time they were installed, new cats and the X cross over were installed, and the noise really did drop by quite a bit, and the performance did improve by a good amount. My first 78, also with the 351M had the factory exhaust manifolds with 2 1/4 inch pipes front to back, with an H cross over and Dynoflow mufflers. It was not significantly quieter than the Flowmasters, and did not have quite the 'oomph' of Nora. Oh, and Nora's noise levels are quite acceptable, and that is saying something since I work in film, on the over night, and need a quiet car.

 

Chevygod, thanks for adding some theory to this discussion, I love it. Now I understand why the exhaust system is 2.25" ahead of the mufflers, and 2.0" behind.

Based on everything I've read here, I think my best path forward is to have the exhaust shop install an H-section and two backwards glasspacks (or resonators) upstream of the mufflers they already installed. If more quiet is needed, I'll add resonator tips.

 

Just in case anyone is thinking straight out the back tailpipes are a good idea, watch this:
http://www.youtube.com/watch?v=h7Gqvu_Z5vc&feature=related