Single vs. Dual Exhaust
Joseph Edward Huesmann
other than looking cool? I read in C&D that the new Supra Turbo was
designed with a single exhaust in an attempt to save the weight of the
extra tailpipe. Ideas? Thanks.
Joe
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| Joseph E. Huesmann the world, she walks into mine!" |
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Stephen D'Amelio
>Are there any advantages to having a dual exhaust over a single exhaust,
>other than looking cool? I read in C&D that the new Supra Turbo was
>designed with a single exhaust in an attempt to save the weight of the
>extra tailpipe. Ideas? Thanks.
The traditional advantage gained by dual exhaust was to create less
back pressure on the engine. If the piston does not have to work as
hard to expel exhaust gases, then you gain horsepower. By going from
one pipe to two, it would be that much easier for the exhaust gases
to exit, thus the engine required less effort to expel it. I guess
you could just have one larger pipe and accomplish the same thing,
especially on 4 cylinder engines. I beleive dulies originated from
the v-8 design, where you have two distinct sides for pipes to exit.
I have a question while where on the subject, I have always been told
that *some* backpressure is a good thing, but I don't know why.
Anyone...
-Steve
Pierre-Henry Marbot
That's because of acoustics!!!
I had a class mate once, who was working on an engine with variable
intake tube lengths. (It was a colledge projet, so he only calculated
the theory!).
The trick is that you always want to have maximum gaz velocity at the
valves, where gaz flow is restricted. Now imagine you have a similar
restriction (carburator, or muffler) at exactely one wave length
away... the friction will be much less (imagine that the gazes
hit the muffler at the point of the wave when they are at maximum
pressure, and there will be a lot of resistance.
If there is no backpressure at all, the engine "feels" the valve
obstruction more.
So he had variable length tube loops (a bit like the musical instrument)
both in the intake and exhaust, a computer would change the length
depending on gaz flow, engine load, rpm's, throttle etc.
He said the effect was like a "half" turbocharger!
Peter
P.S: come to think of it, I do not remember, if you want max pressure
or max velocity at the valve, but that is the line of thought.
Mark J. Vandiver
It has been many a year since I was involved in this stuff, but I
seem to remenber that small ammounts of back pressure helps keep
your exhaust valves from burning/sticking though I know that is what
lead was for in the old gases. I was told the same thing many years
ago, yet I can't remember the exact reason why. I DO KNOW that some
of the newer cars do not even have mufflers (so to speak). The
muffler is actually now just a sensor, a speaker, and another sensor.
The first sensors listens to the engine noise, produces anti-noise
to release from the speaker to cancel th engine noise, and the last
sensor senses how well the anti-noise is doing and corrects to produce
the best reduction in engine noise without adding backpressure! Must
be the newer hardened valve seats that allow this.
>-Steve
Leonard Lauria
>The traditional advantage gained by dual exhaust was to create less
>back pressure on the engine. If the piston does not have to work as
>hard to expel exhaust gases, then you gain horsepower. By going from
>one pipe to two, it would be that much easier for the exhaust gases
>to exit, thus the engine required less effort to expel it. I guess
>you could just have one larger pipe and accomplish the same thing,
>especially on 4 cylinder engines. I beleive dulies originated from
>the v-8 design, where you have two distinct sides for pipes to exit.
>I have a question while where on the subject, I have always been told
>that *some* backpressure is a good thing, but I don't know why.
>Anyone...
>-Steve
gotta have some...at least on the cars i have experience with...i don't
know the mechanics behind it all...but i know that you end up with no
power or much less if you open up the exhuast too much.
leonard
--
===========================================================================
-This space intentionally left blank.
Andrew A. Spencer
In a previous article, leo...@aix3090b.uky.edu (Leonard Lauria) says:
>dam...@progress.COM (Stephen D'Amelio) writes:
>
>
>>The traditional advantage gained by dual exhaust was to create less
>>back pressure on the engine. If the piston does not have to work as
>>hard to expel exhaust gases, then you gain horsepower. By going from
>>one pipe to two, it would be that much easier for the exhaust gases
>>to exit, thus the engine required less effort to expel it. I guess
>>you could just have one larger pipe and accomplish the same thing,
>>especially on 4 cylinder engines. I beleive dulies originated from
>>the v-8 design, where you have two distinct sides for pipes to exit.
>
>>I have a question while where on the subject, I have always been told
>>that *some* backpressure is a good thing, but I don't know why.
>>Anyone...
>
>>-Steve
>
>gotta have some...at least on the cars i have experience with...i don't
>know the mechanics behind it all...but i know that you end up with no
>power or much less if you open up the exhuast too much.
>
>leonard
just guessin' here, but, if you have catalysed exhaust, even if you convert
to duels, and it is functioning properly, you shouldn't have any problems
with to little backressure..
anyone want to comfirm/refute?
hasta
DREW
James P. Callison
>
>In a previous article, leo...@aix3090b.uky.edu (Leonard Lauria) says:
>
>>dam...@progress.COM (Stephen D'Amelio) writes:
>>
>>
>>>The traditional advantage gained by dual exhaust was to create less
>>>back pressure on the engine. If the piston does not have to work as
>>>hard to expel exhaust gases, then you gain horsepower. By going from
>>>one pipe to two, it would be that much easier for the exhaust gases
>>>to exit, thus the engine required less effort to expel it. I guess
>>>you could just have one larger pipe and accomplish the same thing,
>>>especially on 4 cylinder engines. I beleive dulies originated from
>>>the v-8 design, where you have two distinct sides for pipes to exit.
>>
>>>I have a question while where on the subject, I have always been told
>>>that *some* backpressure is a good thing, but I don't know why.
>>>Anyone...
>>
>>>-Steve
>>
>>gotta have some...at least on the cars i have experience with...i don't
>>know the mechanics behind it all...but i know that you end up with no
>>power or much less if you open up the exhuast too much.
As I recall from when my dad and I rebuilt the 390 in my '66 Ford
Galaxie 500, if you run the engine with too little back pressure (such
as when the exhaust manifolds are off), you'll burn the valves up. Too much
reduces power, too little reduces power...
Ironically, tuned exhaust doesn't always make a big difference; one of
the Shelby-American Mustangs proved this. They had a version with
tubular exhaust and a version with cast iron exhaust manifolds; the
hp difference wasn't that great...
James
James P. Callison Microcomputer Coordinator, U of Oklahoma Law Center
Call...@uokmax.ecn.uoknor.edu /\ Call...@aardvark.ucs.uoknor.edu
DISCLAIMER: I'm not an engineer, but I play one at work...
The forecast calls for Thunder...'89 T-Bird SC
"It's a hell of a thing, killing a man. You take away all he has
and all he'll ever have."
--Will Munny, "Unforgiven"
Wayne Smith
>
>I DO KNOW that some
>of the newer cars do not even have mufflers (so to speak). The
>muffler is actually now just a sensor, a speaker, and another sensor.
>The first sensors listens to the engine noise, produces anti-noise
>to release from the speaker to cancel th engine noise, and the last
>sensor senses how well the anti-noise is doing and corrects to produce
>the best reduction in engine noise without adding backpressure!
What cars have this setup?
I know that a setup like this can work, but expending additional energy
to cancel out exhaust noise goes against the trend of automobile energy
conservation (ie just muffle the noise instead).
Brian J Queiser
This kind of active noise cancellation has yet to be put into use
on mass-produced vehicles. The SAE's "Automotive Engineering"
magazine has an article on this subject this month; check it out
for more details. The gist is that, at best, all we'll see on cars
in the not too distant future is tuned exhaust. Currently, the
Mitsu 3000GT VR/1 9000 LXi GT TurBo Landau, the Dodge Stealth, the
NSX, the Camry, and some others employ flapper valves in the exhaust
pipes, stepper valves in the mufflers, or other gizmos to tune the
exhaust to sound sporty, quiet it down, or optimize back pressure.
I did a little research in this area, and I, as well as the SAE article,
can tell you that this business of speakers and sensors will probably
not be able to ever work fully for an affordable amount of money, or
lend itself to much practical use. Engine exhaust doesn't just drone
out at a consistent 200Hz, you know. And cancelling those really low
frequency sounds requires nice big woofers, if you can do it at all
for less than, say, $50,000. If you can, let Bose know, 'cause they've
been workin' on the 3.5" speaker for years and I'm sure they'd like
to know how you can displace that much air. Anyway, this isn't meant
as a flame, just check out the article, it explains everything.
Regards,
Brian
bque...@magnus.acs.ohio-state.edu
------------------------------------------------------------------------
I am the engineer, I can choose K.
------------------------------------------------------------------------
Department of Engineering Mechanics
Ohio State University
Columbus, OH
Tom Coradeschi
>
> dam...@progress.COM (Stephen D'Amelio) writes:
>
> >hues...@wam.umd.edu (Joseph Edward Huesmann) writes:
>
> >>Are there any advantages to having a dual exhaust over a single exhaust,
> >>other than looking cool? I read in C&D that the new Supra Turbo was
> >>designed with a single exhaust in an attempt to save the weight of the
> >>extra tailpipe. Ideas? Thanks.
>
> >The traditional advantage gained by dual exhaust was to create less
> >back pressure on the engine. If the piston does not have to work as
> >I have a question while where on the subject, I have always been told
> >that *some* backpressure is a good thing, but I don't know why.
> >Anyone...
>
> It has been many a year since I was involved in this stuff, but I
> seem to remenber that small ammounts of back pressure helps keep
> your exhaust valves from burning/sticking though I know that is what
> lead was for in the old gases. I was told the same thing many years
> ago, yet I can't remember the exact reason why. I DO KNOW that some
Not entirely correct. The _real_ reason you need to do this is that a
free-flowing exhaust will tend to lean out the mixture (anyone care to
guess why?). If you go to straight pipes, there is the _possibility_ of
leaning the mixture to the point where you _could_ burn the exhaust valve
or its seat. The solution? Rejet your carb if you go to a much more open
exhaust than you had (adding duals w/ mufflers to an originally
single-exhaust vehicle *shouldn't* require this). If you've got fuel
injection (closed-loop), don't worry 'bout a thing.
tom coradeschi <+> tc...@pica.army.mil
Clive Apps
>In article <C3AuE...@constellation.ecn.uoknor.edu> call...@uokmax.ecn.uoknor.edu (James P. Callison) writes:
>>In article <1n0l4o...@usenet.INS.CWRU.Edu> aa...@po.CWRU.Edu (Andrew A. Spencer) writes:
>>>
>>>In a previous article, leo...@aix3090b.uky.edu (Leonard Lauria) says:
>>>
>>>>dam...@progress.COM (Stephen D'Amelio) writes:
>>>>
>>>>
>>>>>The traditional advantage gained by dual exhaust was to create less
>>>>>back pressure on the engine. If the piston does not have to work as
>>>>>hard to expel exhaust gases, then you gain horsepower. By going from
>>>>>one pipe to two, it would be that much easier for the exhaust gases
>>>>>to exit, thus the engine required less effort to expel it. I guess
>>>>>you could just have one larger pipe and accomplish the same thing,
>>>>>especially on 4 cylinder engines. I beleive dulies originated from
>>>>>the v-8 design, where you have two distinct sides for pipes to exit.
>>>>
>>>>>I have a question while where on the subject, I have always been told
>>>>>that *some* backpressure is a good thing, but I don't know why.
>>>>>Anyone...
>>>>
>>>>>-Steve
> exhaust? Yea, I know your talking street cars. This issue has benn
> debated for years. Taking the exhaust manifolds off of your car can
> cause your valves to warp due to cold air being dranw back into the
> engine exhaust port and contacting the hot valves, but it is not due
> to a lack of back pressure. Even street cars that are run at the drag
> stip on week ends run better if equipt with headers that are opened at
> the track, so that restriction is as low as possible. IMHO>>>>
>>>>gotta have some...at least on the cars i have experience with...i don't
>>>>know the mechanics behind it all...but i know that you end up with no
>>>>power or much less if you open up the exhuast too much.
>>
>>As I recall from when my dad and I rebuilt the 390 in my '66 Ford
>>Galaxie 500, if you run the engine with too little back pressure (such
>>as when the exhaust manifolds are off), you'll burn the valves up. Too much
>>reduces power, too little reduces power...
>>Ironically, tuned exhaust doesn't always make a big difference; one of
>>the Shelby-American Mustangs proved this. They had a version with
>>tubular exhaust and a version with cast iron exhaust manifolds; the
>>hp difference wasn't that great...
>>
>> James
>>
>>James P. Callison Microcomputer Coordinator, U of Oklahoma Law Center
>>Call...@uokmax.ecn.uoknor.edu /\ Call...@aardvark.ucs.uoknor.edu
>>DISCLAIMER: I'm not an engineer, but I play one at work...
>> The forecast calls for Thunder...'89 T-Bird SC
>> "It's a hell of a thing, killing a man. You take away all he has
>> and all he'll ever have."
>> --Will Munny, "Unforgiven"
>
>
THE REASON THAT SOME CARS REQUIRE BACKPRESSURE TO RUN PROPERLY IS THAT
THEY ARE USING A CAMSHAFT WITH TOO MUCH DURATION FOR THE APPLICATION
VALVES BURN BEACAUSE THEY ARE HOT AND EXPOSED TO OXYGEN NOT BECAUSE
OF REDUCED BACKPRESSURE
REDUCING BACKPRESSURE HELPS TO REMOVE HETA FROM THE ENGINE FASTER
AS THE EXAUST CAN ESCAPE BETTER
FOR HIGH FLOW AND LOW BACKPRESSURE USE AFTERMARKET PERFORMANCE CATALYTICS
OR 2 CATS FROM A 76-78 CCHRYSLER NEW YORKER WITH A 400
THESE ALL HAVE MONOLYTHIC DESIGNS AND 2 1/2" INLETS AND OUTLETS
USE A BALANCE TUBE OR "H-PIPE' DESIGN THIS WILL ENHANCE LOW END TORQUE
HIGH END POWER AND REDUCE NOISE NOT A BAD DEAL FOR SOMETHING THAT COSTS NEXT TO
NOTHING TO INSTALL