X pipes and V engines
Discussion
Hey all, I was just watching a video of an SLS AMG with an aftermarket exhaust made by Supersprint. In one of the uploader's comments, they mentioned that V engines need a crossover in the exhaust system somewhere and that using two straight pipes will just make it sound like two four cylinder engines together. Is this really the case? Is the V8 burble created by the exhaust gas pulses mixing within the exhaust system?
I would have thought that the two cylinder banks of a V engine would have generally mixed in a shared part of the exhaust system at or above the downpipe where the manifold for each cylinder bank joins together. Having never had the chance to poke around under the bonnet of a V engined car, I might be missing something. So am I right, in that there is a common part of the manifold where the gases mix before the exhaust, or are they kept separate until after (presumably seperate) catalysts?
I would have thought that the two cylinder banks of a V engine would have generally mixed in a shared part of the exhaust system at or above the downpipe where the manifold for each cylinder bank joins together. Having never had the chance to poke around under the bonnet of a V engined car, I might be missing something. So am I right, in that there is a common part of the manifold where the gases mix before the exhaust, or are they kept separate until after (presumably seperate) catalysts?
I'm sure all sorts of clever acoustic effects can be acheived by messing around with this, and it may well be that the crossover makes that particular engine sound at it's best. I'm sceptical, however, that the sound could be described as merely 'two 4-cylinder engines'- some of the best sounding V8's run an open header from each exhaust port 
Its accepted that an H pipe (i.e. a straight pipe that runs between the two parallel exhausts) is a good idea. The yanks call them balancer pipes, the theory is it balances out the exhaust pulses.
X pipes are a more recent thing, the advantage over an H pipe is that they are meant to improve scavenging of exhaust gases. Some swear by them, other people prefer H pipes and quite a few people think there is little difference between them.
Random article I found:
http://www.carcraft.com/techarticles/exhaust_syste...
X pipes are a more recent thing, the advantage over an H pipe is that they are meant to improve scavenging of exhaust gases. Some swear by them, other people prefer H pipes and quite a few people think there is little difference between them.
Random article I found:
http://www.carcraft.com/techarticles/exhaust_syste...
Most V8 engines (including the SLS) have a cross plane crank. Not going to go into to much depth now, but it means the engines firing order is as balanced as it can be. One of the consequences of this is that the firing order is uneven on each bank. So, as the engine rotates, at some point the left hand bank will fire twice, and then the right hand bank will fire. The firing order for my Stag is like this:
l,r,l,r,r,l,r,l
Given that, even if you could only hear one bank firing, it would still have that off beat woofle that makes V8 so distinctive. It'll never sound like a normal 4 cylinder, which of course fires evenly.
Other V8's have a flat plane crank (usually high revving ones, Ferrari's etc) and they have even firing on each bank. If you could only hear one bank it would sound just like a 4 cylinder engine, these engines do not have the characteristic off beat burble most people associate with a V8.
I understand that the downside to a cross plane crank is that the inlet/exhaust isn't smooth, something I assume crossover pipes attempt to mitigate.
The exhausts on my Stag are completely separate until about half way down the system where there is an 'H' pipe just in front of the first set of silencers.
l,r,l,r,r,l,r,l
Given that, even if you could only hear one bank firing, it would still have that off beat woofle that makes V8 so distinctive. It'll never sound like a normal 4 cylinder, which of course fires evenly.
Other V8's have a flat plane crank (usually high revving ones, Ferrari's etc) and they have even firing on each bank. If you could only hear one bank it would sound just like a 4 cylinder engine, these engines do not have the characteristic off beat burble most people associate with a V8.
I understand that the downside to a cross plane crank is that the inlet/exhaust isn't smooth, something I assume crossover pipes attempt to mitigate.
The exhausts on my Stag are completely separate until about half way down the system where there is an 'H' pipe just in front of the first set of silencers.
Edited by varsas on Sunday 27th November 21:08
varsas said:
I understand that the downside to a cross plane crank is that the inlet/exhaust isn't smooth, something I assume crossover pipes attempt to mitigate.
Ah yes, I had heard something about this when reading about how turbo engines make it difficult to get a decent sound from the exhaust, as the turbo causes a constant stream of exhaust gas, smoothing out the pulses from the firing order / crank angle etc. I had noticed too, that flat-crank engines like Ferraris did have a less burbly sound in general, although the 458 has a distinctive quack on the over-run that I don't usually assosciate with Ferraris.On another interesting note, Yamaha added a crossplane crank and irregular firing order to the 2010 R1 bike, similar to Valentino Rossi's M1 GP bike, it sounds fantastic.
Mastodon2 said:
varsas said:
I understand that the downside to a cross plane crank is that the inlet/exhaust isn't smooth, something I assume crossover pipes attempt to mitigate.
Ah yes, I had heard something about this when reading about how turbo engines make it difficult to get a decent sound from the exhaust, as the turbo causes a constant stream of exhaust gas, smoothing out the pulses from the firing order / crank angle etc. I had noticed too, that flat-crank engines like Ferraris did have a less burbly sound in general, although the 458 has a distinctive quack on the over-run that I don't usually assosciate with Ferraris.On another interesting note, Yamaha added a crossplane crank and irregular firing order to the 2010 R1 bike, similar to Valentino Rossi's M1 GP bike, it sounds fantastic.
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