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Dual vs Single exhaust question

Started by mistertudball, April 11, 2014, 05:30:30 PM

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mistertudball

I've always wondered this so I thought I'd ask some folks who probably know.  Generally speaking, is the main reason some cars come with single exhaust and some with duals mostly manufacturer expense?  Seems to me an early 70s Eldorado with what I think is the largest production engine ever (500 ci) would merit duals, yet it doesn't.  I just looked at a 70 Buick Wildcat 'vert with a 455 4 barrel and it also has a single.  And these were supposed to be the "performance" models for the brands, I thought.  Do some enormous engines run better with a single?
David Bartosic CLC19619

bcroe

Quote from: mistertudball on April 11, 2014, 05:30:30 PM
I've always wondered this so I thought I'd ask some folks who probably know.  Generally speaking, is the main reason some cars come with single exhaust and some with duals mostly manufacturer expense?  Seems to me an early 70s Eldorado with what I think is the largest production engine ever (500 ci) would merit duals, yet it doesn't.  I just looked at a 70 Buick Wildcat 'vert with a 455 4 barrel and it also has a single.  And these were supposed to be the "performance" models for the brands, I thought.  Do some enormous engines run better with a single? 

Engines run better without a lot of exhaust restriction/back pressure.  Generally its easier
to add a second parallel exhaust than to double the cross section area of a single exhaust,
though either will reduce back pressure. 

When cat converters went on, initially there was only one.  That meant the engine was
already forced to a single pipe, which usually would be run the rest of the way back.  Those
larger engines were restricted in peak power, not hard to measure.  Later cars used a much
improved monolithic cat, and sometimes more than one, to recover performance. 

A car may not feel much different when converted to duals.  But the torque will not fall
off as much at peak rpm, and a stop watch will clearly show the difference.  Bruce Roe

Alan Harris CLC#1513

Dual exhausts were kind of a fad between about 1954 and the middle sixties. I can't think of many cars after about 1968 that came with them.

I suspect that the manufacturers thought of them as more of a styling feature than anything else, since they looked cooler than a single exhaust, especially on the more expensive cars when they were routed through the bumper.

If the volume of the single exhaust is as large as the combined volume of the duals, I don't see much of a performance difference between them.

The duals tend to run cooler, which increases condensation and rust. They don't last as long and they are more expensive to build and to replace.

The Tassie Devil(le)

When looking at the Exhaust of the vehicle, one also has to look at the Intake of the engine.

It is a waste of time putting duals on when the air cleaner inlet has such a small hole for the air to enter.   Case in point is the '72 Eldorado.   Air Cleaner hole is tiny compared with the capacity of the Spreadbore Carby, and therefore the whole engine is restricted right from the start.

Plus, don't forget that a single system is cheaper to produce, and runs quieter, which is what Cadillac is all about.

The reason that the cars with the X Chassis had Duals was, I believe, that it was simpler to place the tubing on the outsides of the "X" Member, and then rearwards.   These '50's frames made it difficult.   When the Perimeter Frames came in, Single was so much simpler.

The time to go Duals is when increasing the air intake (open up the Air Cleaner spout), enlarge the intake and exhaust valves and compression.   Then the gases can get out.   Plus, you get a nice "note" and the only way to get a nice note is with increased compression.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

TJ Hopland

Then there was all the stuff that had the dual outlet muffler.  Seems like that started with the Chev trucks in the 80's?  80's F bodies I think were like that too?   Those had an outlet on each end of the muffler if I recall correctly?   Seems like a lot of stuff came that way starting in the 90's if you had the 'performance' V6 option.   All that stuff was in the cat era so I suppose it was maybe for looks?  But saving money by only having one cat?   Is there some logic to more free flowing after the cat and muffler?  I suppose anything helps?

Did the 90's V6 trucks had dual cats like the V8's?   How about cars?  I assume many had a single cat but some did have 2?    Thinking about it in the 90's the GM trucks kinda reversed their earlier system where they had dual cats into one muffler then one outlet / tail pipe. 

My 2005 Dodge car with the Hemi V8 had 2 cats that went into a big flat square muffler so 2 ins and 2 outs.  The outs went to 2 resonators back near the tail pipes.   I never saw a diagram of the muffler internals but I assume there was at least some connection between the two halves.   I would guess that is the H or X pipe concept built into a single muffler. 

If I ever have the money to spend what I am thinking I want to do with my 73 Eldo is dual inlet muffler with single oversize outlet that will likely run to a resonator and tail pipe.   A shop showed me a muffler that looked like it would be a good physical fit.  They said they would install it first without the res to see if I was happy with the sound.    I have a full custom dual system on there now and even if it was done a little better it just does not fit well.  If I did not want it quiet it would be easier but with the physical size of 2 quiet mufflers there just is not room to keep it tucked up nice and close so they end up hanging down.   Its also tight going over the rear axle with 2 pipes and then tight around the gas tank with the left pipe since the tank was apparently shifted to the left to make room for the resonator.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

mistertudball

Thanks.  All of this made perfect sense.  I'm going to have to do some exhaust work on the '73 Eldo in the fairly near future and didn't know if I should blow the budget by going to a dual system.
David Bartosic CLC19619

76eldo

I don't know about 73's but the 76 Eldo fuel tank is mounted in such a way that there is room for the resonator on the right side, but no room on the left.  This makes installing a set of duals on a 76 Eldo a challenge.

At least your 73 is a free flowing system without the stupid cast iron "box" where the y pipes meet head on and then the Cat is bolted to the next pipe back.  This truly is a choke point.  My 76 needs a new system anyway, so I am looking into getting a 71-74 system and eliminating the Cat and the cast iron box.  A free flowing system on this car HAS to improve performance at least a little bit.

I have an NOS intermediate pipe, and an NOS over the axle pipe and resonator, just need the muffler and the two front pipes and I will have the complete system.

Brian
Brian Rachlin
Huntingdon Valley, Pa
I prefer email's not PM's rachlin@comcast.net

1960 62 Series Conv with Factory Tri Power
1970 DeVille Conv
1970 Eldo
1970 Caribu (?) "The Cadmino"
1973 Eldorado Conv Pace Car
1976 Eldorado Conv
1980 Eldorado H & E Conv
1993 Allante with Hardtop (X2)
2008 DTS
2012 CTS Coupe
2017 XT
1956 Thunderbird
1966 Olds Toronado

DeVille68

Great question. I still do not fully understand the importance of an exhaust system.
I heard that if you change from single to dual exhaust or if you replace the muffler by a better free-flow design you will also change the back-pressure conditions.
It is said that low back-pressure gives you better peak horsepower but reduces the low rpm torque.

So, when I would like to have an more aggressive sound on my caddy and I install, for example a Flowmaster HP-2, I will have less torque?
And even worse when converting to dual exhaust?

Hence, relating to the first post, it would make sense to optimize the exhaust to give the proper back pressure since these big engines (455 cid) were mainly torque machines?

Can anyone give a explanation from an engineering standpoint?

Regards,
Nicolas
1968 Cadillac DeVille Convertible (silver pine green)

The Tassie Devil(le)

This is how I did my own twin system in my '72 Eldo.

Because the fuel tank was off-set to the left side, I had to run the pipes out the right side.   Took a bit of ingenious bending and running of the pipes, but we got it there.   And all Stainless Steel.

No ground clearance problems either.   In picture 003, you can see part way down the straight tubing, there is a pair of slight flattening of the tube.   This allows the pipes o sit up higher under the Torsion Bar crossmember.

Using a lot of flanges allows me to remove where necessary for maintenance of other parts of the car.   All welded, or clamped exhausts are a pain when needing to access anything.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

mistertudball

WOW, most impressive!  If you ever get bored, I have another one you could work this magic on.
David Bartosic CLC19619

Gene Beaird

Quote from: bcroe on April 11, 2014, 07:22:06 PM
<SNIP>But the torque will not fall
off as much at peak rpm, and a stop watch will clearly show the difference.  Bruce Roe

^^ This.  Probably 99% of the Cadillacs ever produced would never run WOT through their peak RPM, so there's no need for the manufacturer to pay for the extra parts that won't matter much at all over the lifetime of the car when the owner wants to see lighted vanity mirrors and power windows. 

Seeing as how you have a car that's probably never going to see the high side of 70 MPH on the highway, or the drag strip, I'd opt for a nice 3" mandrel-bent single and call it a day.  Spend the money on a stainless system, instead of two pipes.  But that's my opinion. 
Gene Beaird,
1968 Calais
1979 Seville
Pearland, Texas
CLC Member No. 29873

mistertudball

But then there's always the 1965 Olds Starfire (a personal fave) with its duals exiting those chrome ducts just ahead of the bumper.  Needlessly cool!  And only one year.  Hmmmm
David Bartosic CLC19619

Thule

damn.. that dual is nice,  you got a soundclip?
Ivar Markusson.  icelandic cadillac club (part of CLC)
73 Eldorado coupe.

The Tassie Devil(le)

Would be nice if I knew how to do it.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

mike mason

Time to replace the exhaust system on the 50.   It's tired & part of a sort of a rebuilding project.  Been giving some serious thought to a dual exhaust.  In 52+ there were dual exhausts, but there was also slightly more compression, and a switch from a 2 to a 4 barrel carburetor.  How much of the increased performance was due to the dual exhaust in measurable terms.  Believe everything else was the same, and how much more could be gained from switching to the 4 barrel.