Other than making it sound louder?
In: Technology
The idea is that having a full-sized exhaust pipe system on both sides will let the engine breathe better. There is more room for the engine to exhale.
A car that has a front-engine/rear drive, and it sits close to the ground…a dual exhaust has a purpose. The early 1960’s Mustang and Camaro are a good example.
The base model had a six cylinder and a single exhaust. The performance version had a V8 which needed a bigger-diameter exhaust tube in order to prevent back-pressure in the exhaust, so the engine could breathe easy at high RPM’s.
The problem was that the early Mustang and Camaro did not have a lot of room underneath for a larger single muffler and exhaust pipe. The hot pipe should not be too close to the fuel tank, or brake hoses, or other things underneath.
By breaking the exhaust system into two separate runs of the same-size of tubing, you could easily fit enough breathing capability. Soon after that, the fact that a car had a single exhaust tube poking out, or a dual exhaust…it became a way to identify the “performance” version.
There are many examples of a vehicle model having a dual exhaust when it doesn’t need that. It’s just for show to make it look sporty.
If you take in more fuel and air to get more power/speed out of the engine, you need to be able to expel the exhaust. If you don’t have enough on the ass-end, you’re going to choke out the engine when you start bringing in more and more. Dual exhausts actually allows your engine to exhale more efficiently, allowing it to operate more efficiently.
I don’t think there is any reason why it would make it louder actually. But “dual exhaust” can mean different things. It can actually be fake, it could be a single pipe split to two at the very end.
Each cylinder in an engine will have a pipe coming out. These are called the headers. They can come out of the engine in different ways. Sometimes they’re all separate and then merge together later. 4 pipes may merge to one. Sometimes they all come out and connect into one long pipe that runs along the engine. I believe that would be called an exhaust manifold and not a header.
Typically if you have a v8 engine you’ll have 4 pipes coming out of each side of the engine that reduce into one. So then you have two pipes to go out the back.
You may also have a mid pipe which can be an X or H shape. All of this is to combine the gas pulses in different ways for efficiency or to stop droning sounds.
In that v8 each cylinder has a little explosion that occurs and that pulse of exhaust gas shoots out. You get many explosions occurring and shooting out the pipes in a certain firing order. How you collect and combine those gas pulses plays into how the engine performs and sounds.
There’s a ton more to it that can’t be explained simply. I’ve seen so many videos on exhaust gases, back pressure, scavenging and I know enough to say I don’t know enough to explain.
Combustion engines need air, fuel and a spark to go boom and make power. After the boom the exhaust has to go away so more air and fuel can go into the cylinder to boom again. (Suck, squeeze, bang, blow). Larger exhaust improves the blow portion.
A larger or dual exhaust speeds up that last part. It doesn’t really need to be dual, but two small tubes= one big tube when you can’t fit one big tube under the car/truck. Also allows flexibility in how you move the byproducts (heat) of the exhaust.
A dual exhaust on its own won’t make it louder, it just so happens that for all the reasons everyone else has stated, dual exhausts tends to be used for higher performance vehicles which naturally are louder for various other reasons.
An internal combustion engine is basically a fancy air pump.
The amount of fuel put into an engine needs an accompanying amount of air in order to be fully burned, so the amount of ‘power’ a given engine can make is completely dependent on how much air can be sucked in, and then pushed out, and how easily. This is why putting a Supercharger or Turbocharger will usually increase the power of an engine, because it will cram more air into the engine that if it was “naturally asperated”.
This is why a smaller engine that can operate at a high RPM, can make an equivalent amount of power as a big low RPM ‘V8’. It spins faster to pump an equivalent amount of air.
If you address all of the airflow issues of the intake side, then the bottleneck becomes how easily your engine can shove the air out of it’s cylinders once combustion is complete. A dual exhaust, or bigger/high flow aftermarket exhaust will help with the bottleneck.
With that said, **the bottleneck of a given engine is almost always the intake side**, because in a *naturally asperated* engine there is ‘vacuum’ as your pistons try to suck in as much air as they can, whereas exhaust, because it’s already in the engine, has to go **somewhere** once the piston starts pushing it back out of the combustion chamber.
Getting air in is always harder than getting air out. Like blowing up a balloon.
This is why on engines that have an uneven number of valves in a cylinder (Like the Ford ‘Triton’ V8, or some Toyotas had 5 valves per cylinder) there are always more intake valves than exhaust valves. In an engine with 2 valves per cylinder (The most common configuration) the intake valve is almost always bigger than the exhaust valve.
This means that, unless you’ve increased the amount of air that can flow into an engine* **first**, dual exhaust or an aftermarket ‘fart can’ exhaust nets almost zero power gains, and just makes a tonne of extra noise.
*Manufacturers will sometimes release ‘high output’ versions of their engines that can flow more air, and thus need the bigger/dual exhaust.
The simple answer is that dual exhaust pipes have a larger overall capacity for flower, which increases performance. Plenty of cars come stock with dual exhaust and they aren’t loud. You associating when you notice dual exhaust with custom muffler jobs that happen to also be louder.
Most other commenters give perfect answers about exhaust flow and low back pressure and minimizing undercarriage profile and all that, but we all know the REAL answer.
So the 20th century Corvettes could have those kickass double-paired pipes matching their double-paired rear lights, of course!
There is also the admittedly-rare rear-mounted boxer engine, in which case a dual exhaust is simply extremely convenient.
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