Safety, comfort, noise and space are the things that come to mind.

Safety

Exhaust gasses are hot as hell. Hot enough that we put heat shields all over the exhaust line. In engines, we are actively trying to remove heat. Adding more from the exhaust goes completely against that and would increase overheating. Also, would you want a hot exhaust pipe near your door, nicely exposed for you to brush a leg against when getting out? I don't.

Comfort

If the exhaust came out the front or the side, you would be far more likely to breathe in your own exhaust, either through an open window or the ventilation system. No thanks.

Noise

We need to put a muffler somewhere. The space near the engine is already being used pretty heavily. So you would either have to design something smaller or live without one. Since there are laws some places regarding having a muffler and creating excess noise, car manufacturers are going to put them on there so they can sell cars.

Space

As alluded to above, there are large components (muffler, catalytic converter) that need to go somewhere. And they don't fit up by the engine.

好吧，我們 可以有一條從汽車前部伸出的管子，如下所示： 或更重的前身： 可以說，兩者的空氣動力學特性都不都是最佳的，但這是一種確定了空氣動力學的類似方法： 其他設計（例如卡車）確實考慮了空氣動力學將排氣管放在相關正面的後面，並使排氣流向側面或上方排出。儘管我懷疑它的用處，但您甚至可能會在乘用車中看到它：

所有這些情況的共同點在於，設計師有足夠的空間來以便將氣體從駕駛員/駕駛員的鼻子引導走。

您可能在大多數標準的工廠模型乘用車設計中都沒有這個特性。因此，必須以不同的方式解決該問題。從工程師的角度來看，情況更加惡化，您將不得不適應廢氣處理設施和消音器某處，而諸如DPF / SCR系統（柴油機廢氣清潔）之類的裝置將佔用大量空間。自己的：

幾件事；

1. 從前面出來的排氣很危險。如果將煙霧吸入駕駛室，可能會傷害駕駛員。通常，汽車會向前行駛。如果廢氣從後部排出，則煙氣進入駕駛室的可能性最小。
2. 消音器是大型組件。發動機艙內通常沒有足夠的空間容納它們。
3. 排氣聲嘶啞。背部的長途旅行使它變涼了。沒有人會想要一輛汽車，如果您路過，就會被燒死。
ol>

The exhaust also creates a pressure differential, which can help scavenge exhaust gases from the chamber. So a properly tuned exhaust will therefore increase the fuel efficiency of the engine. Whilst an engine without an exhaust would make more power, it would also consume more fuel.

Adding to the excellent answers already given.

• An important point to note is that we need to have a catalytic converter somewhere in the exhaust a short exhaust will not have room to fit it.

Then there are a host of other things car manufacturers determine while designing an exhaust system.

For an engine to have optimum efficiency, the intake , combustion and exhaust systems have to be tuned together as a single entity. The exhaust is more than a stupid long steel pipe at the end of the exhaust manifold. It CONTRIBUTES to the performance of the engine.

Within the exhaust itself there are various parameters like the length, the width or the diameter etc which determine a host of factors.

For example, if you want a setup with low end power and good efficiency , you will have to go for a traditional long exhaust, if you want a race setup a short exhaust is preferred.

So for any car you drive , the exhaust pipe characteristics are carefully adjusted and tuned according to the purpose of the car , now in 90% of the commuter cars , the performance factor takes a back seat and economy and comfort come in first , thus the long exhaust till the tail.

Now , one can argue that if length of the exhaust affects the performance then why do super cars have long exhausts? Reason? to stick to Sound and emissions standards.

Take that airplane with the short, up-front, direct exhaust pipes. Start it up in your driveway early on a Saturday morning. See how popular you are with your neighbors.

因為已經指出，地獄式內燃機具有危險的副產品-熱和有毒氣體以及噪音-需要從使用車輛的人身上帶走。一個世紀前，社會做出了一個錯誤的選擇，而我們生活在今天的後果中。買一輛電動汽車，您永遠不必更換排氣/尾氣管。但是，您仍然必須注意減速帶。