Technical Exhausts - one or two?

[Ucof]

This is a general car question here.

I pulled up behind a normal newer style Renault Clio last night and my eyes ended up at the exhaust. I noticed that it had two out pipes from the same back box, and wondered why this was.

At first I thought it could be engine size related, but then realised that my old two litre van only had one exhaust.

Is it just to do with styling, or is there an actual reason that a car would need two (or more) exhausts?

 

[Chas Uno]

Look at most touring cars that the road cars are based on. How many exhausts do they have? Question answered!

Twin exhausts are more often fitted to 'V' engines or engines with multiple banks of cylinders (flat fours, flat sixes), with one exhaust connected to one bank of cylinders and the other connected to the other bank. Older straight six engines could also sometimes have twin exhausts with each connected to one pair of three exhausts ports.

For most road legal four cylinder cars I seriously doubt that they make a lot of difference compared with a well designed single exhaust system. The fact that Chavs fit fake twin exhausts makes the 'styling' aspect of it even worse! No idea on the Renault though, unless it was the V6 model (which would then make sense).

You're not thinking of fitting a twin exhaust are you?

 

[randomspeedfreak]

yeah the new clio sport has 2 exausts but just a straight 4.
its ridiculous and pointless to put 2 exhausts.

adds nothing but weight and expense......i suppose it gives people that really know how to make their cars go fast something to laugh at

dont do it

 

[Ucof]

Hell No Im not planning on twin exhausting it. I hate chavved up cars, and already feel guilty about the smaller chrome radio aerial I put on, seeing as I hardly listen to the radio.

Yeh, the Clio had a single back box with two exhaust pipes coming out of it. i think that that was what confuised me and amde me want to ask.

 

[Chas Uno]

Ah, so you're talking twin outlets from a single back box rather than a twin exhaust system (see pic)? That I don't know but I suspect it's more for show than anything else. Once again, look at real race cars and see what they have for exhausts and most of the time they have a single pipe per exhaust back box. Twin outlets might be something to do with keeping noise levels lower, possibly due to changing the reverberations in the system but again I don't know for sure. What matters is allowing exhaust gases to pass through the system without restriction, therefore having two smaller outlets in a back box rather than one larger outlet probably makes no difference at all.

 

[Ucof]

Yeah, it was like the shiney exhaust in the bigger picture, rather than an actual twin exhaust system.

 

[bartvanraamsdonk]

And is it me or are double exhausts on one backbox always hanging out of alignment?

 

[alexGS]

There are some Toyota models around - Trueno/Levin 1996-ish and probably not in England at all - that have twin exhausts as standard from a four cylinder, one each side of the car. A large back box visible below the bumper runs across from one outlet to the other. To make things even more puzzling, on a cold morning you see more water vapour from one outlet than the other. That makes me suspect that the exhaust takes the easier route out of the first outlet it gets to, and the second outlet on the other side is for high-speed scenarios. Toyota obviously did that for some reason and I hasten to point out that these cars are whisper-quiet, both outlets being modestly sized (this is BEFORE the usual tuner-brigade get their hands on the cars).

I can't see this being required or desirable for much of the time, but I thought I'd share it just in case.

As for efficiency - on a four-cylinder you definitely want the exhaust from all four cylinders to combine at some point, usually somewhere near the front of the floor, and there's no advantage in running separate pipes to the rear of the car. As Chas said, that's done for each bank of V- or flat-engines.

-Alex

 

[PaulDrage]

to be fair to Renault i think the clio 2 182 sport is well designed and this is one point i bring to the table, the exhaust diameter from manifold down to the backbox is rather large (i used to work on these a lot), it then goes into a large rear box, and has two outlets, in my mind there is a couple of reasons:
1- style (without a doubt), Renault made the 182 look 'pretty' which is not a bad thing for sales i have no doubt.

and 2- they can have 2 outlets/pipes out of a single box that are a smaller diameter, they do not want to have a single 6" tailpipe so have two smaller ones.

And because its the manafacturer that fitted it I assume it is already doing everything for the power of the vehicle that it can output wise, because it produces 182bhp from a 2.0 (no turbo) engine, with some fuel economy etc.

I think if the car was designed with twin exit pipes in mind (i.e bumpers moulded right etc) then they look nice, but when you slap twin pipes on an uno, well.

 

[Jai]

I think if the car was designed with twin exit pipes in mind (i.e bumpers moulded right etc) then they look nice, but when you slap twin pipes on an uno, well.