Why Most Quad Tail Pipes Are Completely Pointless
CT News Editor Matt Robinson is one lucky man – he’s managed to get his hands on the new Civic Type R as a long-term test car (the jammy git). And yet after an inspection of the fairly obnoxious rear, a question arose; are those huge quad exhaust tips for show or for go?
Honda isn’t the only manufacturer which seems to love a multitude of exhaust outlets, each worthy of the Alex Kersten ‘Fist Test’. To begin with, it must be made clear that each exhaust tip on the Civic is functional; every tail pipe has exhaust gases flowing out of it and therefore has a function. Many manufacturers have even less class and decide to provide fake tips that only serve as a cover for a single exhaust outlet, with a close-up glance exposing the illusion.
In truth, most four-cylinder vehicles would only ever really need a maximum of two exhaust outlets due to the lack of power that they produce. Even with hot hatches merging into so-called ‘super hatches’ like the Type-R and Focus RS, 300bhp is still a relatively small amount in the grand scheme of things. This means that the amount of exhaust gases produced by each revolution of the engine is minimal in comparison to larger capacity powerplants.
Seeing as the Civic Type-R is turbocharged, this changes things up in terms of exhaust sizing. To increase the pressure and therefore the velocity of the air entering the turbocharger, the headers are often smaller in size than on a naturally aspirated engine. Thereafter however, ‘turbo-exhaust’ systems are designed to have as little back pressure as possible to maximise the inlet velocity to the turbocharger and therefore a designed to be larger in diameter. However, the effects on exhaust flow from turbochargers of the size found in the Civic Type-R would be minimal in the grand scheme of forced induction. This means that despite an overall increase in diameter over the entire system, the relative size of the exhaust tips found on the Type-R are definitely over the top.
The dimensions of an exhaust system generally follow the theory behind something called Volumetric Flowrate. This is simply the volume of gas that can be extracted from a system in a given time, which can be directly correlated with exhaust systems. It is calculated by the multiplication of the cross-sectional area of the exhaust tubing and the speed of the gas flowing through it:
The main aim of an exhaust system is simply to get the waste gases from the engine out to the surroundings as quickly and efficiently as possible. So if you want the exhaust gases to move quickly, you restrict the diameter of the exhaust to form a small area which increases the pressure of the exhaust gas and accelerates it down the tubing. Restrict the exhaust too much however and you result in inefficient turbulent flow which can cause back pressure. Alternatively, if the exhaust bore is too large, the speed of the gases leaving the engine will be dramatically reduced. A compromise between the exhaust size and efficiency must therefore be found.
In terms of the exhaust tips, the only real function is to influence the tone and volume of your exhaust note. This is because the relative speed of the exhaust gas flow is depleted by the time it gets to the outlet of the system, therefore influences on the actual dynamics of the airflow can be neglected.
Like the Type-R, most exhaust tips provide a small expansion from the exhaust tubing before it. Using the Volumetric Flow Rate calculation, this means the exhaust gases will slow down, reducing the tone of the exhaust noise and creating what can be an extremely satisfying warble from the tail pipes. I’m sure Matt will provide us all with an exhaust note video at some point on Car Throttle Extra. So to answer the question, the quad tips on the Civic Type-R are really just for show and for a specific exhaust note with no tangible gains in performance influencing the design.
Although let’s be fair, they look sick af. Long live needless additional tail pipes.
Comments
Science!!!!!!!!! (physics to be precise)
And Chemistry because GASES!
When I was a kid I believed the more exhaust pipes the faster the car
Agera and Veyron have only one exhaust. They must be slow af
By that logic, the P90 Tesla sedan (or any Tesla car for that matter) has no exhaust pipes.. and therefore must not even move.
Tesla p85d?
Wel then must the last car be a beast
“A turbocharger recycles exhaust gases from the engine to spin a turbine which in turn spins a larger turbine which forces air back into the cylinder to produce more power. This means that less of the total exhaust gases produced by the engine after each piston’s cycle makes it to the end of the exhaust system.” Please explain.
Bullshit. A turbocharger increases the chemical reaction’s product quantities because it increases the quantity of air entering the cylinder and since oxigen only takes 20% of “air”, the rest 80% is pure waste But, just using logic, more air enters but less gas comes out? That’s why there are “turbo” exhaust systems, they are built for higher temperatures and pressure.
This, a turbo system pushes more air in the engine so as a result there will also be more comming out. A turbo actually NEEDS a bigger diameter exhaust because too much restriction would hinder correct wastegate operation and increases turbo lag.
This statement in the article is not correct. When you look at the basic principles of thermodynamics, there is a thing called mass conservation. It basically means that what enters a “control volume” must also come out (assuming a steady flow process). What is used to drive a turbo is not the exhaust gas itself, but rather the energy it has (think pressure and speed of the gas), which it transfers using the turbine wheel, so if anything the velocity and pressure of the exhaust gas decreases (and therefore the energy), but the mass remains the same. I hope this helps :)
Volumetric it becomes less, but not in the amount of substance going through. This is because of the fact that a turbo is using the excess heat of the exhaust to feed more air into the engine. This cools down the gas, and as one learns in school; warm gas is less dense than cold gas, hence the misunderstanding that “less of the total exhaust gases (…) makes it to the end of the exhaust system”. I think that was what they meant to say
I hope that’s an error.
what comes in, comes out, the turbo doesn’t magically make some of the gases disappear!
Some people do that because OCD, I know I would do that… if I had Need for Speed.
Isn’t it pointless to even have a dual exhaust on a car with an inline engine? The manifold almost always (in 95% of the cases at least) ends as one pipe, no matter whether it’s a 4-, 5- or 6-cylinder engine. So theoretically you would always only need exactly one exhaust pipe, or a maximum of two on a V or boxer engine.
Well, at least I suppose. Correct me if I’m wrong.
Makes sense to me. Maybe you split them towards the rear for the OCD-inclined people. Who knows?
True, but after the collector you can either go with a split and use a smaller diameter exhaust or you can use one big exhaust all the way trough. It ends up a design/sound decission what’s best at that point. Sometimes a big diameter exhaust won’t clear the diff etc etc.
Yep thats true. You can look at the Veyron, and I think almost all Königeggs if I remember correctly, they all have a single exit point, even though the Veyron has a fin in the middle to reduce turbulence.
May be different to meet emmisions- and noise-tests. If you couple that with performance stats you may end up with a more effective system having an I6 engine with a dual exhaust manifold system.
It’s more of a size issue. The bigger the engine the bigger the pipe has to be and since it’s impractical to have a 10” pipe, it gets devided to two 5” pipes.
Also if it’s a rear mounted boxer it’s obviously more practical to have two pipes instead of one
(by bigger I mean compined quantity of gas in the chambers mesured in liters at full stroke)
Exactly, who has 4 fists anyway…
VW does probably need them on the Golf R because exhaust gasses
It is literally mentioned in article that this is not neccessary. Even more funny, the Golf VII R exhaust actually is a single pipe that only splits into two pipes (which themselves split into two pipes each) after the last muffler. It really is nothing but an exterior design decision.
What did you said ?
Hmm. Your physics is slightly off there. Even with a turbo no air ever goes back into the cylinder. A turbo simply forces more in. You’ve always got to have the same going in as coming out. If anything your have more your have more volume out as its hotter. The only time exhaust goes back through the engine is with EGR which I don’t think is what you were referring too.
Exactly… the only thing that the exhaust gas does is spin the turbine to compress the air. The actual air to be compressed comes from the environment, so it isn’t like any of it is leaving the system.
The idea behind the article is interesting. The information however, doesn’t make much sense…
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