Why do factory exhausts have flexible sections in them?

[Ark]

Just that really. I'm trying to figure out if there's something useful I'll lose by sticking in a straight decat or high-flow cat pipe.

 

Initially I thought that if the whole pipe was solid, engine vibrations would shake the entire pipe around...cue cracking. Then I read something about the flexibility introducing drone because of vibrations.

 

So, who knows best?

[JustGav]

Just that really. I'm trying to figure out if there's something useful I'll lose by sticking in a straight decat or high-flow cat pipe.

 

Initially I thought that if the whole pipe was solid, engine vibrations would shake the entire pipe around...cue cracking. Then I read something about the flexibility introducing drone because of vibrations.

 

So, who knows best?

 

I suppose the flexible's could introduce harmonic reasonance which would cause even more damage.

[georigg]

Hi Ark,

Depends, I think on whether you are referring to front wheel drive or all cars.

 

FWD engines tend to rock "backwards and forwards" as a result of the engine being across the way and this movement will result in cracked exhausts, hence there is almost always a "flexible" joint, like a ball joint on the exhaust or a flexible pipe section.

 

Rear wheel drive cars almost always have the engine running front to back(mid engines are an exception but usually have "short" exhaust runs so are hung off the engine), so with RWD the engine is rocking side to side which does not put so much of a strain on the pipework, although some RWD cars also have a "flexible" section to allow for this small turning moment, which is much smaller usually than FWD cars.

Rgds

George

[Ark]

That makes sense George. I am of course referring to the Supra, which still has a flex in the downpipe, despite the engine layout.

 

And why oh why have a flexible joint at the top of the DP, and fix it to a solid bracket at the bottom of the DP?

[bignum]

I think its to allow for expansion.

[matt k]

It probably reduces movement of the exhaust and therefore stops it from potentially knocking?

[Matt H]

I'd thought it was pretty simple really, if you have a solid section of what is quite a heavy part spanning all the way from the block, down the manifold and to the rear of the car, the stress on the parts from movement at the back of the system would be quite severe at the other end where its attached to the block. allowing flexible sections, like they do anything long (like drainage for instance) reduces the moments and effects of movements along the entire pipe.

 

stress reduction in other words

[Swampy442]

Stress reduction, by allowing expansion/contraction and reducing transfer of vibration and flexing to the rigid sections of the system