dual exhaust vs. larger single exhaust
Ed Treijs
Yaakov Eisenberg <yaa...@cc.gatech.edu> wrote:
> I'm curious about what the advantages are (if any) of a dual exhaust
>system over a single exhaust system of equivalent total cross section
>(e.g. 2 1" pipes vs. 1 1.414..." pipe). On the one hand, lots of people
>use dual exhausts, and probably at least some of them know what they're
>doing. On the other hand, I've seen discussions in various rec.autos.*
>groups which generally advocated the use of crossovers on dual exhausts,
>and one of the reasons given was that a crossover would enable all the
>cylinders to help scavenge each other. It seems that a single exhaust
>system might do this even better.
Far as I can figure, the single pipe with the same cross-sectional area
as the two duals would be *superior* in flow, because there's less tube
wall in the single pipe to affect gas flow. Put it another way, if there's
a boundary layer next to the pipe that affects flow, it takes up less
percentage of the total cross-section in a big single pipe than in two
smaller pipes.
A single pipe can also let you use a single, honkin' big muffler, which
may very well offer better flow as well as lower sound levels than a
couple of cheesy small mufflers. Finally, the single system probably
warms up faster, and therefore is less likely to rust out. (Again,
volume vs. surface area arguments.)
However, there's only so big you can go with pipe. A single 3" pipe is
probably equal or better than two 2 1/4" pipes, but ain't no custom
bending shop gonna be able to do a nice job. If you can get a pre-made
3" pipe, go for it!
Also, having a single 3" pipe means futzing around with getting the two
manifolds connected, and that opens up a whole can of worms. OEM
installations usually have a crossover from the left manifold, under
the engine, to the right side where the exhaust runs back. This
obviously can be pretty restrictive.
In practical terms, a nicely-bent dual system will just be easier to
set up and make flow than any custom-bent single pipe. For most older
cars, there is no DynoMax etc. custom BIG pipes (for 2nd-gen F-bodies
the best is 2 1/4" SINGLE pipe....for the 3rd gen you can get 3"; but
the 2nd gen had much bigger motors, so go figure).
By the way, finding an intelligent muffler shop is a quest in itself.
Ed (found one in Toronto, though) Treijs
Kelly Murray
|> may very well offer better flow as well as lower sound levels than a
|> couple of cheesy small mufflers. Finally, the single system probably
I've been thinking that a good low-cost way to go for muffling a
V8 1/4 mile car to keep performance similiar to non-muffled,
would be to have 3" pipes coming off the collectors
on each side and then have each side split into two 2.5" pipes
that feed into two glasspaks and then up and over the rear and
out the back. So you get 4 mufflers, but lots of air volume.
Is this not a good idea? Is it better or worth the money
to run 3" pipe and two 3" mufflers?
-Kelly Murray (k...@prl.ufl.edu) <a href="http://www.prl.ufl.edu">
-University of Florida Parallel Research Lab </a>
Douglas O. Toms
: specific recommendations for my car -- a '69 Dodge Coronet, 318 engine.
: I'm considering getting a supercharger for it. What kinds are good?
: Where can I get one? What would be an appropriate exhaust system if
: I got a supercharger? if I didn't?
:
: Any info having even some slight relevance to this would be appreciated.
: Thanks.
:
: --
:
: -Yaakov Eisenberg (yaa...@cc.gatech.edu)
If you're thinking of supercharging a 318, the first thing I would do
would be to get some good heads. The 318-2 bbl heads have very small,
restrictive ports that would not work well with a supercharger.
If you get 340 heads, with 2.02 intake valves, I believe that you have to
get the block notched for valve clearance, but not if you get 360 heads
with the 1.88 intakes. The ports on the 340/360 heads are twice the size
as on the 318-2V.
Forged low-compression blower type pistons and a forged crank will also
likely be required, but I'm sure there are other people with more
experience in this area. You might want to go to a 360, if you're going
to spend all that money on a performance rebuild.
Doug Toms
Dirk Broer
> I'm curious about what the advantages are (if any) of a dual exhaust
>system over a single exhaust system of equivalent total cross section
>(e.g. 2 1" pipes vs. 1 1.414..." pipe). On the one hand, lots of people
>use dual exhausts, and probably at least some of them know what they're
>doing. On the other hand, I've seen discussions in various rec.autos.*
>groups which generally advocated the use of crossovers on dual exhausts,
>and one of the reasons given was that a crossover would enable all the
>cylinders to help scavenge each other. It seems that a single exhaust
>system might do this even better.
For starters most dual exhaust are 2.25" minumum and up. This would be at
minumum equivalent to a single 3" system.
A high velocity gas moving past a port - perpedicularly - will cause a vacuum -
I guess this is what helps low rpm scavaging. At higher rpm having dual paths
to let the gas out may help - especially once the gas starts to cool. Wisdom
has it that the cross-over should be place past the point where the headers/
exhuast gets below a certain temperature. Story like paint a line down the
exhaust - put the cross-over past the point at which the paint doesn't burn off
.
Dual exhaust is also easier to work with - especially for pulling
transmissions etc.
> I'm interested in general information about this topic, and also any
>specific recommendations for my car -- a '69 Dodge Coronet, 318 engine.
>I'm considering getting a supercharger for it. What kinds are good?
>Where can I get one? What would be an appropriate exhaust system if
>I got a supercharger? if I didn't?
First, consider a 340 or 360. They have a bigger bore and allow the larger
valve heads to work. 318 is not bad - it just shrouds the valves worse then
the other two.
If you don't already have it get the Mopar Engine and Mopar Chassis books.
You may have some trouble finding bolt-on kits. I think you also have a 2bbl
carb (I had a '70 318) makes it even tougher.
I would be that many changes would have to be made - I would suggest thinking
the project through from the ground up.
Step one get a budget. By the time you beef up the engine etc. it will easily
cost $6000 including the supercharger and all the little parts. You can do it
cheaper I'm sure but not reliably.
You should also budget for for updating the chassis of the car. If you car has
the 7.75" rear you will almost certainly want a posi rear (not available stock
in a 7.75) and updated springs and shocks at the very minimum. Skinney tires
won't cut it either.
You should also budget some chassis stiffening. Mopar uni-bodies + traction
+ high torque equals bent body. Bend point seems to be front spring mount -
YMMV
Do you want to cut a hole in the hood or not? This would decide what kind of
supercharger.
The Roots type blowers normally require a hole in the hood - contact Weiand,
Crager, maybe B&M.
For no hole in the hood (and maybe lower boost levels) contact Paxton - they
may have a kit.
These companies can give you an idea of what is required _in_ your motor.
So after you add up decide if its worth it. Throwing thousands of dollars at a
car that isn't your dream car will quickly get old and you'll never finish -
let alone recoup any of your money.
A mopar B-body is a heavy car and considering all the money your going to spend
it might be better for you to buy an old Barracuda or Dart and take it from
there. You'll spend the same money just get a faster car out of the deal.
No matter what supercharger you choose - you'll make the most power with
headers and dual exhaust. You'll probably want 2.5" pipes. With all the low-
end torque of a supercharger a cross-over won't do much (make things a little
quieter).
Good Luck
Dirk
S.I.Le...@massey.ac.nz
>system over a single exhaust system of equivalent total cross section
>(e.g. 2 1" pipes vs. 1 1.414..." pipe). On the one hand, lots of people
>use dual exhausts, and probably at least some of them know what they're
>doing. On the other hand, I've seen discussions in various rec.autos.*
>groups which generally advocated the use of crossovers on dual exhausts,
>and one of the reasons given was that a crossover would enable all the
>cylinders to help scavenge each other. It seems that a single exhaust
>system might do this even better.
>specific recommendations for my car -- a '69 Dodge Coronet, 318 engine.
>I'm considering getting a supercharger for it. What kinds are good?
>Where can I get one? What would be an appropriate exhaust system if
>I got a supercharger? if I didn't?
>
>Thanks.
>
>--
>
> -Yaakov Eisenberg (yaa...@cc.gatech.edu)
In New Zealand and Australia the deal is to fit a big single pipe. Some are
using 2 1/2" others 3" or bigger if it fits. As this tends to be on
engines about 350 cubes or less,there appear to be no flow problems.
The first reason is cost. less parts labour time.
2nd: more heat retained in the single pipe so any moisture is more
readily evaporated. (as an aside a book written in 1960-62? by Vance Packard
"Planned Obselcence" states that for this very reason dual exhausts
were promoted so they would rust out sooner!, despite the performance
advantages.)
3rd: A single is easier to fit in a modern car, some just don't have the
room for a second pipe.
4th: some dyno tests have been tossed about showing that some engines "like"
a single big pipe over a dual setup. Pulses, scavenging??
5th: A single is quieter in general and a hot motor thru a single really
sounds different!
THE KIWI
Eric M. Webb
>From: yaa...@cc.gatech.edu (Yaakov Eisenberg)
>Subject: dual exhaust vs. larger single exhaust
>Date: 11 Jan 1995 21:21:07 -0500
> I'm curious about what the advantages are (if any) of a dual exhaust
>system over a single exhaust system of equivalent total cross section
>(e.g. 2 1" pipes vs. 1 1.414..." pipe). On the one hand, lots of people
>use dual exhausts, and probably at least some of them know what they're
>doing. On the other hand, I've seen discussions in various rec.autos.*
>groups which generally advocated the use of crossovers on dual exhausts,
>and one of the reasons given was that a crossover would enable all the
>cylinders to help scavenge each other. It seems that a single exhaust
>system might do this even better.
Yaakov,
The challenge with exhaust systems is twofold- to expel gases in such a way
as to prevent excessive backpressure and to allow the gas to flow at the
proper velocity. The two problems to overcome are harmonic resonance and path
resistance.
A dual exhaust system can accomodate the exhaust pulses from each bank of
cylinders, which fire alternately in a V6 or V8 engine. These pulses create
sonic waves that bounce about and cause a distortion like that you can hear
when sound waves feed back into an emitting source such as a microphone.
Reducing constrictive bends in the tubing and muffling helps remove the
non-productive bouncing. However, some wave bouncing is good. Some very good
mufflers use 45 degree angles to bounce and partly neutralize or dampen sonic
waves while promoting a relatively free flow through the device.
The crossover pipe, or resonator, does assist in scavaging gas from the
bank not currently in the exhaust phase. But correctly designed, they can
help eliminate sonic disturbance, even in a 90 degree "H" implementation.
The pipe diameter and gas flow are subject to a simple physical law stating
that the velocity of the flow is inversely proportional to the diameter of the
tube through which it flows. Man-made materials, external vibrations and
phases of the moon prevent absolute relationships, but one can toss these
aside and use this law as a good rule of thumb. Basically, given a constant
pressure, a gas will flow faster through a tube with a smaller diameter than
one with a larger diameter. Using the size of the tube, you can control the
velocity of the gas flow.
Using a tube that is too large for an application is just as bad as using
a tube that is to small. Too large and the velocity is not fast enough to
keep optimum air flow through the entire system. Too small and the system
becomes constipated with backpressure because too little gas is flowing
- although it is flowing very fast.
The general effects upon engine performance between the two extremes
where the system is inefficient are:
1. Smaller pipes enhance low-RPM torque.
2. Bigger pipes enhance high-RPM horsepower.
Upon approach to the boundaries there is a more noticeable tradeoff of one
property for another. For example, you may increase low-end torque at the
expense of high-end horsepower.
Remember that every part of the air flow system is related to changes in any
one part. If you're goal is too increase torque to the maximum degree, you
need to consider changes to the intake manifold, camshaft profile, exhaust
manifold or headers, collectors, and mufflers.
> I'm interested in general information about this topic, and also any
>specific recommendations for my car -- a '69 Dodge Coronet, 318 engine.
>I'm considering getting a supercharger for it. What kinds are good?
>Where can I get one? What would be an appropriate exhaust system if
>I got a supercharger? if I didn't?
I can't speak to this combination. But exhaust manufacturers like Borla and
Flowmaster and supercharger makers like Paxton and Vortech can. And of course
you can't beat the practical advice of those who have modified this make and
model. I'm sure they will suggest good combinations. Have fun making it move
faster :-)
Regards,
----------------------------------------------------------
Eric Webb / Martin Marietta
79 Alexander Drive, Bldg 4501 / RTP, N.C. 27711
Phone: 919-541-7896 Fax: 919-541-0028
Eric M. Webb
>From: k...@prl.ufl.edu (Kelly Murray)
>Subject: Re: dual exhaust vs. larger single exhaust
>Date: 12 Jan 1995 20:57:22 GMT
>|> A single pipe can also let you use a single, honkin' big muffler, which
>|> may very well offer better flow as well as lower sound levels than a
>|> couple of cheesy small mufflers. Finally, the single system probably
>I've been thinking that a good low-cost way to go for muffling a
>V8 1/4 mile car to keep performance similiar to non-muffled,
>would be to have 3" pipes coming off the collectors
>on each side and then have each side split into two 2.5" pipes
>that feed into two glasspaks and then up and over the rear and
>out the back. So you get 4 mufflers, but lots of air volume.
>Is this not a good idea? Is it better or worth the money
>to run 3" pipe and two 3" mufflers?
It, and more complex ideas, have been done and run successfully. IMHO, things
simple seem to work and break less. Something relatively new that folks are
doing is using performance catalytic converters up close to the collectors,
thus allowing more freely flowing mufflers (eg Borla, SuperTrapp) downstream.
The dual cats will dampen the sound without restricting the air flow much.
This won't work with a leaded gas car. But it limits the amount of pipe and
pipe splitting (which can introduce some unwanted noise) and allows for a nice
straight flow. Plus, late model cars stay legal and older cars run cleaner.
I did this on my 68 476 cid Camaro with 3" exhaust pipes.
David Studly
<S.I.Le...@massey.ac.nz> wrote:
>> I'm curious about what the advantages are (if any) of a dual exhaust
>>system over a single exhaust system of equivalent total cross section
>>(e.g. 2 1" pipes vs. 1 1.414..." pipe). On the one hand, lots of people
>>
[snip]
>5th: A single is quieter in general and a hot motor thru a single really
>sounds different!
>THE KIWI
I'll agree with this - a friend of mine had a '79 LeMans that he fitted
with a decent 327/2800 stall converter/4.10 rearend. The car ran a best
of 13.2 @ 102 (open exhaust) but he had this kludged together exhaust
system that was routed through a single turbo muffler for the street - it
did sounds pretty cool, especially ay 6000-6500 RPM!
-David Studly, david....@ohiou.edu
Dirk Broer
>A single pipe can also let you use a single, honkin' big muffler, which
Gotta find a 3" inlet and outlet muffler. FlowMaster racing muffler - or maybe
the Dodge V-10 truck muffler (its got a really big outlet!)
>However, there's only so big you can go with pipe. A single 3" pipe is
>probably equal or better than two 2 1/4" pipes, but ain't no custom
>bending shop gonna be able to do a nice job. If you can get a pre-made
>3" pipe, go for it!
Penn autoparts (used to be called Penn Jersey) has an exhaust bending machine
locally. Bring in a coat hanger bent to the right shap and they'll give you a
pipe back. For long relatively straight pipes make the shap out of 1x2 wood.
>Also, having a single 3" pipe means futzing around with getting the two
>manifolds connected, and that opens up a whole can of worms. OEM
>installations usually have a crossover from the left manifold, under
>the engine, to the right side where the exhaust runs back. This
>obviously can be pretty restrictive.
Look in circle track magazine - some classes require cast iron manifolds. The
hot ticket is corvette ram-horn types modified for 3" exhaust. The two 3"
pipes connect via a "y" and exit out the back. Supposidly this 2/3 as good as
a header system.
Dirk
FLHTC
Ed,
That is totally BULLSHIT, if a single exhaust system flowed better then
a dual I think manufactures would have but single systems on then dual !
Also racers would have gone with a single set up long ago !
Tony
Ed Treijs
>From: etr...@bnr.ca (Ed Treijs) writes :
>
>>Far as I can figure, the single pipe with the same cross-sectional area
>>as the two duals would be *superior* in flow, because there's less tube
>>wall in the single pipe to affect gas flow. Put it another way, if
<some of my text deleted>
>>However, there's only so big you can go with pipe. A single 3" pipe is
>>probably equal or better than two 2 1/4" pipes, but ain't no custom
>>bending shop gonna be able to do a nice job. If you can get a pre-made
>>3" pipe, go for it!
>
>>Also, having a single 3" pipe means futzing around with getting the two
>>manifolds connected, and that opens up a whole can of worms. OEM
>>installations usually have a crossover from the left manifold, under
>>the engine, to the right side where the exhaust runs back. This
>>obviously can be pretty restrictive.
>
>>In practical terms, a nicely-bent dual system will just be easier to
>>set up and make flow than any custom-bent single pipe. For most older
>Ed,
>
> That is totally BULLSHIT, if a single exhaust system flowed better then
>a dual I think manufactures would have but single systems on then dual !
>Also racers would have gone with a single set up long ago !
>
>Tony
Hello? You reading what I wrote? You want maybe to deny that, oh, a 12"
diameter single pipe will flow well? Eh? "Doh, but it wouldn't fit on
the car, dude!" --Exactly my point. Much easier to fit duals, plus
don't have to worry about the crossover. Gee, what I wrote.
Also, of course, there is the "hey, I got dual pipes" stoopid poser thing.
Just like "my carb is way bigger than yours, my cam is way bigger than
yours, so I must be faster than you" crap. Building up a good-running
car takes more than reading every Chevy Craft and buying everything in
the ads.
Racers, on the other hand, don't have to worry about mufflers (usually),
catalytic converters, and asphyxiation problems. Takes little rocket
science to figure that two short straight pipes running from each header
collector is the way to go. And it SHOULDN'T take rocket science to
figure that "racers do it like X" usually doesn't mean squat on the
street.
Sheesh. AOL, eh.
Ed (mildly peeved) Treijs
Sandwich Maker
[]
" That is totally BULLSHIT, if a single exhaust system flowed better then
"a dual I think manufactures would have but single systems on then dual !
"Also racers would have gone with a single set up long ago !
it may be so for v8s but i've talked to s6 racers, and those who've
tried them say that 6->2->1 'crosstuned' headers make more power than
6->2 duals.
--
although you should be doing something productive
with your life, you are instead wasting your time
reading this inane mindless rambling drivel from
the keyboard of: Andrew Hay, a...@andr.ub.com