Dual exhaust vs single exhaust

[rfcr]

Hello All,

I'm wonder what the pros and cons of a dual exhaust system are. As I'm sitting here waiting for parts to come in I started thinking, which seems to get in trouble most of the time, if this would help or hurt my engines performance (when I get it running). If anyone has a free minute and an opinion I would like to hear it. Thanks

[Plymouthy Adams]

get it running..if the engine will not hold oil pressure, idle proper, perform on command..dual exhaust will only make the obvious poor running engine more obvious to the casual by stander's ear....it is good to scheme and plan but be sure that your platform is solid before going out on a limb

[Dodgeb4ya]

More mufflers to replace. More pipes in the way of a clutch job.

[pflaming]

Its simple, the exhaust system takes away the exhaust fumes. Dual pipes do it faster than a single pipe. Neither make the engine run better. Therefore get the engine solid and sound first then work on secondary items such as dual carbs and dual exhaust. IMHO

edit: On my B3B I am stock to the muffler. I was given an (I think stainless steel) Flow-master muffler. It has larger inlet and outlet pipes and we kept the outlet pipes large. My hearing is very bad so don't know how it sounds.

Edited July 11, 2014 by pflaming

[Lumpy]

I've always thought that the stock manifold is pretty good, has a good outlet diameter, looks to be pretty free flowing. I don't doubt that tuned tubular headers, or the two/twin/dual cast iron manifolds would flow better, but "how much" is the question...especially considering the low RPM nature of our engines. ??

 

I think the stock exhaust manifold is a pretty good unit, as long as the head pipe is full diameter, and you keep that diameter all the way out to the tail pipe, don't neck it down at the muffler, or after the muffler. That's probably pretty free flowing.

 

I'm also thinking that if one did run dual exhaust manifolds, they would probably work best going into a full size (same diameter as the exhaust manifold's outlet) Y-pipe, with a 2.5" pipe coming off the Y-pipe/collector, and then a single, free flowing 2.5" muffler, and a 2.5" tail pipe....rather than running two pipes and two mufflers. I think that would flow better.

 

k.

[Plymouthy Adams]

outside the ooh and ah factor and the sound of a decent split...yeah..waste overall...you need a proper cam and induction to really make it all come together..

[Andydodge]

Yeh but wouldn't it be boring if we all had just a single exhaust......lol..........stock is good......but I'm a hotrodder so varoommmm!.........the guys are right tho'.....get it running well then treat it to a low restriction exhaust, wack a bit off the head and maybe an extra carby..........and go hunt some Frods & as Don C says Shivolays.........lol........andyd 

[ledfootslim]

I've always thought that the stock manifold is pretty good, has a good outlet diameter, looks to be pretty free flowing. I don't doubt that tuned tubular headers, or the two/twin/dual cast iron manifolds would flow better, but "how much" is the question...especially considering the low RPM nature of our engines. ??

 

I think the stock exhaust manifold is a pretty good unit, as long as the head pipe is full diameter, and you keep that diameter all the way out to the tail pipe, don't neck it down at the muffler, or after the muffler. That's probably pretty free flowing.

 

I'm also thinking that if one did run dual exhaust manifolds, they would probably work best going into a full size (same diameter as the exhaust manifold's outlet) Y-pipe, with a 2.5" pipe coming off the Y-pipe/collector, and then a single, free flowing 2.5" muffler, and a 2.5" tail pipe....rather than running two pipes and two mufflers. I think that would flow better.

 

k.

Wouldn't the flow be better with two seperate 2.5's going into individual mufflers, than both going into a y-pipe?

[50desotocoupe]

Don't forget you need some amount of back pressure for a scavenging effect. 

 

http://www.gomog.com/allmorgan/exhaustbackpressure.html

[desoto1939]

Just think of the extra cost to do this and for what. Maybe a couple of mile per gallon more if that or the sound. Or jsut put in a big V8 inthe car with straight pipes and you willget the sound you want. But then with the bigger engine you willhave to chnage the fron configuration, possibly front disc and rear disc brakes, then want tilt steering wheel, ac bigger tires and chromies, tinted glass and it keeps going on,

So if this is what you are looking for then go buy a completed Hotrod. I am not trying to be smart answered on your question, pleae understand that.

If you want an antique then there are certain things that go with the car and remember the technology that was available back then. So the big question is how deep are your pockets and what do you personally want to do with the car. Some like old stock, some like some old stock with some upgrades some like a lot of up grades and some like total upgrade and hot rodded machines. To each their own style. Basically just enjoy the car and have fun with it.

Just my opinion and not to discourage you from doing what you want to do, its your car.

Rich HArtung

[1941Rick]

As for power increase, it is the same power increase you get on a Harley with straight pipes. If noise equates power you get more power. A L6 with a split manifold

has a cool sound. Mines was very powerful and cool. Reds headers into 2 1/2" pipes thru Thrush glass packs. As a matter of fact too cool and powerful. Had to put in a crossover pipe to cut the cool factor.. Now have the right combination of cool and power.

Its all the WOW factor.

I hope some one sees my sarcasim.....

[Mark Haymond]

These flathead six engines are easy to work on and have a good reputation for reliability. That's their charm, a 60 year old engine that can still be a daily driver.  My advice would be to install a single MAGNAFLOW muffler which will give a pleasing engine burble at idle but will run quietly on the highway. A FLOWMASTER, a different muffler, on the other hand, is loud all the time and can make it hard to hear conversations at highway speeds.

[55 Fargo]

If I could afford to pay for it. I would build a 265, have a good block, just need the rods and crank. Have the usual, mild /wild cam grind, Edgy head, headers, tri-carb intake, and any other item to allow engine to run at higher RPMs.

It may not be a 300 hp engine, but would have plenty of kick, wow factor and sound cool too.

Hey just woke up, nice dream anyway.....

[jeffsunzeri]

Sounds like nobody has done a strict before-and-after comparison of stock exhaust versus dual exhaust for gas mileage and/or HP. That would certainly be interesting.

I seem to recall some magazine people doing fuel consumption test with V-8's in various cars showing that going from single to dual exhaust was just about easiest and most sure-fire way to increase both HP and mileage.

Anyone know of any old articles or research done on flathead sixes?

[Robin (UK)]

The first change I made to my Plymouth was to add a split manifold and dual exhausts - and the difference was huge.
The motor ran far more freely and with greatly increased torque through the range.

Here is some period info, which also shows an increase in power with dual exhausts, but after the other changes had already been made.

 

Two pages attached.

Two to follow.

[Robin (UK)]

Page 3

[Robin (UK)]

Page 4

[Plymouthy Adams]

Just think of the extra cost to do this and for what. Maybe a couple of mile per gallon more if that or the sound. Or jsut put in a big V8 inthe car with straight pipes and you willget the sound you want. But then with the bigger engine you willhave to chnage the fron configuration, possibly front disc and rear disc brakes, then want tilt steering wheel, ac bigger tires and chromies, tinted glass and it keeps going on,

So if this is what you are looking for then go buy a completed Hotrod. I am not trying to be smart answered on your question, pleae understand that.

If you want an antique then there are certain things that go with the car and remember the technology that was available back then. So the big question is how deep are your pockets and what do you personally want to do with the car. Some like old stock, some like some old stock with some upgrades some like a lot of up grades and some like total upgrade and hot rodded machines. To each their own style. Basically just enjoy the car and have fun with it.

Just my opinion and not to discourage you from doing what you want to do, its your car.

Rich HArtung

Rich...most folks here are going for the balance of the old and the new...I personally am one of them...I love the looks of the old cars but the charm of the flattie and three on the tree is something that does not light my fire..keeping the flattie and going the way of boosting that would have been popular at the time with the shaved or aluminum head, split exhaust, dual aces  and mild cam really do put some zip in these cars and the sound is most gratifying I assure you.  I love the V engines myself but I do not like brap or loud exhaust...there is moderation in all that we can do and to that end you can find balance and harmony in this hobby...I have a couple here that will remain stock..they are just that deserving as they are solid one owner cars or have never in their entire life been wrecked or dinked with by a PO...these are the candidates for stock and even with that can suck it up and live with a three on the tree...drive it at night when no one can see the silly right arm Hitler Salute to second gear..

[desoto1939]

Ply Adams:

I also get your point. It also depends on the currnet condition inwhich you are starting your project. If you have a great original car that has the original engine and the body does not need much work if maybe very little and the interior is in great shape Then I prefer to try to keep them as original as possible. Maybe some upgrade on the wiring, lights maybe to halogin bulbs etc.

But if you are starting with a diamond or a mild diamond in the rough and have to do alot of work then by all means make the major modifications since you have to do so much work to get it back on the road.

Yes I agree that making modifications to your liking is eveyone option and by keeping original also has it set backs. SOme of those are driving at Night, driving on freeways but that is a choice that the individual owner has to decide on with their car.

I prefer to keep as original as possible but I also do like what some of you are doing with the speed equiptment and also the period correct add ons. I prefer the period add ons because this is what also was availble to the hot rodders of that time period and is keeping the car somewhat period correct.

Again I am not discouraging anyone to modify their car. That is what makes the hobby so interesting and I like to see what other ideas people have.

Yes I will make som mods on my 39 Desoto and one day willconvert over to the sealed beam kit even though I do not like the looks of it onthe car but eventually I will need this so I can use the car at night. But that is down the road but will also keep the original headlight configuaration if the next owner wants to convert back.

Keep the ideas flowing, there are some great ones out there.

You talk about the silly second gear of the three on the tree. But by going to that setup the car manufactures now chnaged how many people could sit inthe front seat. Yes some still like the old bamboo shifter onthe floor and yes they are fun to drive. But as the cars evolved so did improvements that came with progress even though not liked by everyone. Just take the Airflows. Great idea in aerodynamcis and safety which later on was implemented in our modern cars. SOme disliked it totally other loved the look and how the cars handled and drove down the road.

Rich Hartung

Edited July 11, 2014 by desoto1939

[Lumpy]

Whether the exhaust would flow better through a big Y-pipe and single exhaust, or dual exhaust all the way, I guess only a dyno could tell us that. I'm thinking that the Y-pipe would scavenge better, but maybe not. It's just how I would do it.

 

Most Harley engines, by the way, put out more power with a two-into-one exhaust system, rather than a single pipe on each cylinder. A cross over also boosts power. But some headers that make the most power, on a V8, will have two of the pipes go into a collector, then those two collectors feed into another collector, so that's why I was thinking of the Y-pipe being another collector which would give a better scavenging effect, but....where's that dyno??? Split manifolds, and dual pipes and mufflers might indeed be best.

 

How much improvement you get from doing exhaust mods depends on how restrictive the system was in the first place. Small pipes, cheap Midas mufflers, is going to be restrictive. And that's what you usually find on the 1940's cars. I don't doubt that a split exhaust system is the ultimate, and "best", but I also think that the stock manifold is pretty good, and will flow good if it's not choked down by stepping down the pipe diameter, or using a wally world muffler, small tail pipe, etc.

 

P.S. I LOVE my three on the tree!

 

k.

Edited July 11, 2014 by Lumpy

[Lumpy]

Interesting old article. I was surprised that they got less gas mileage...but it reinforced my belief that going dual carbs, with the stock carbs is not the way to go. When I went to two carbs, I used B&B's off of 198 slant sixes. More CFM between the two than the single stock carb, but not doubling the CFM which I think is way too much carb. My gas mileage went up, and I also shaved my head quite a bit. I'm running the stock exhaust manifold, but with big pipe (not stepped down at the manifold) and a glass pack that's a straight through muffler, no louvers or baffles.

 

ken.

[pflaming]

I love the '...salute to Hitler" when shifting into 2nd. I grew up with the '50's cars so I like the exercise involved to drive them and I like the hum of the engine when it levels out when on the freeway. I have a Flowmaster muffler which may be contributing to the cab noise which I'm trying to reduce.

This has been an interesting thread. Since I have a '54 suburban to complete upon our return from Maine, this kind of thread is very helpful. So as a result of this thread, it will have a single exhaust pipe and a single carb.

Edited July 12, 2014 by pflaming

[rfcr]

Very interesting reading. I would like to thank all those providing opinions.

[Don Jordan]

I probably shouldn't say this but there is an old saying about peeing in a wet suit: nobody will notice but it feels warm inside. I put dual carbs/exhaust just for me. I don't care if it makes the car run better or not - it just makes me feel warm. I also got a tach for the same reason. I drive from Southern California to Sacramento every year to go the state fair. The car is a tool, I use it as such, just as they did in 1948.

I know this isn't a technical response, just from the gut.

[Ward Duffield]

2x0=0