In transverse engine applications, some manufacturers put the exhaust extractor forward between the engine block and the radiator (eg, Campro, Honda City L15 etc.), some put it rearward between the engine block and the firewall (eg, Lancer B11, Vios 1NZFE etc.)

What are the design considerations when deciding which side the extractor goes?

1st!

Second!

Third

before TS taruk us let me put something for him to read...

Exhaust at the front is the traditional arrangement, it allows the exhaust to be cooled by the air that's come through the radiator (ok, not cold air but still cooler than the exhaust) and allows an exhaust of a given length to be straighter when running beneath the car. Historically (like, in the 90s) intake manifolds have tended to be broader (in terms of the distance between the cylinder head and the opposite side of the manifold) than the exhaust which allows the whole drivetrain and front wheels to be placed closer to the nose of the car. The downside is that the engine has to be placed higher up to allow the exhaust to run beneath it which raises the car's centre of gravity.

Exhaust at the back allows a lower placing of the engine which lowers the car's centre of gravity and current intake manifold designs are (from what I've seen) less bulky than their predecessors so the drivetrain can still be kept close to the nose of the car. In designs that utilise a front subframe, the whole subframe can be placed lower as there's no need to leave space for the exhaust to run beneath it. The disadvantages are that there's a lot less of a breeze to cool the exhaust and it's much harder to get at when it needs replacing.

The reason is simple. Cheaper for manufacturing.

Then all modern cars should put it near the firewall right?

Which type is cheaper?

Ok, joke aside, I too share some of my opinion.

Exhaust manifold at the front end allows engine to sit nearer to the firewall, thus will create a much more "neutral" handling car, supposed to the weight of power train is directly on top of the axle, rather in front of the axle. I believe this setup allow for a tighter engine bay space allocation, and reduces the need of thick firewall since lesser heat build up at that particular area.

Exhaust at the front also provide an easier approach to install a turbo setup, which I am not sure whether is there any model that come with the same engine but higher variants is preequiped with a turbo system. Maybe car manufacturer is considerate?

While exhaust the other way around maybe due to emission controls. Older engine produces more pollutants that need a higher operating temperature for the cat con to work it's best. Thus by creating a warm area within the exhaust manifold and firewall to bump up the cat con temp.

Exhaust manifold which exits behind.

In some engines the intake manifold can be just as bulky as the exhaust extractor, I think that would also push the engine in the opposite direction too? ie, place the extractor in front so you can put the engine further back, but the intake manifold is just as bulky that it negated the advantage.

Or because the intake manifold is so bulky that had to put the exhaust extractor in the back




This post has been edited by dares: Sep 23 2016, 09:05 PM

While cost is a factor, I don't think it is a major one. I see cheap cars with front extractors and expensive cars with rear extractors too

Don't over think about the exhaust. The real reason FWD engines have exhaust in the front is because they are designed by 4 season countries. Mostly cold. So the heat would be spread to engine and defrost everything and engine could reach operating temp faster.

When cars reached Tropical climates, heat is a problem. So mounting larger radiator would solve the problem. Anyone who owned 1980s cars would know what exhaust heat intake for air filter is. Even the old 1980s Saga has the heat intake hole on the air filter.

Back then all cars had summer and winter modes. The design stuck on till today.

The other reason why exhausts are not made to face passenger cabin is because of fire hazard. You could read about melting shoes stories from 1970-1980s cars with such exhaust setup.

So the front extractor is a legacy design from way back when.

Why was it moved to the back then? and why the front design ia still being used?

Some people back then found out a short exhaust route created different power delivery. Also lesser metal used save cost?. Someone in Malaysia did that to a Waja engine many years ago. Said got improvement in power. And that engine is the most simple one to do, but needed new custom exhaust manifold. But that was long ago. Sometimes you get this,



Better power or not is debatable. When i was hanging out with Toyota 20V people time, engine tilting does create power. By adding shims to the engine mounts to tilt it. Much like how V engines angle 60 or 90 degree. Inline 4 Transverse FWD engine seems to have more benefit of tilt than an inline 4 longitunal RWD engine.

Dun think too much about exhaust being front or back of engine. The real magic is the whole exhaust from manifold to muffler.

Good info, thanks for sharing. This engine tilt thing is new to me, I'll google more

Actually the extractor placement thing is more of a curiosity on my part. I wondered if it was a performance or packaging consideration (or both), your answer seems to suggest that it is probably a packaging issue more than anything else, at least for the regular bread and butter cars. Correct me if I am wrong though.

In any case, great share