Faulty Dansk Sports silencers - Cut up

[Alex]

You're only talking a distance of around 30cm from the cat clamp to the backbox clamp and the temp of that stainless gets no where near 300c so your figures are well off.

The temp will be hotter between manifold and cat and there's no flexi on them.

 

[ndg]

The expansion is from the manifold flange to the muffler mounting bracket, the joints are essentially solid once they have been bolted up. As I said, I don't know the EGT's for an M96, I've seen EGT's of 900C on (very high) performance engines before (NA), so was taking some off of that as a best guess. The CAT's are part of the expanding pipework, and obviously their temp will be higher than the downstream pipes, 300C was an average, and a guess at that. Even at 200C the logic would stand - 3mm of movement would be enough to fatigue components over engine heat cycles.

Please feel free to suggest an alternative reason why dansk and Porsche would put an expensive additional component in their exhaust system.

 

[Alex]

The cats are bolted directly on the engine and fixed in that position so with your theory the system would expamd out either way from the center. Like I said - everything is solid on the manifold side so expansion can't be a problem. If it were 300c your rear bumper would melt.

They put flexis on to enable you to replace the exhaust sleeves without having to remove the back boxes - that was my understanding as to why they had them.

 

[ndg]

Just looked at the etk and looks like my car has lost that bracket at some point so I wasn't aware of it. That said, it looks like it has as degree of flex designed in.

I'm going to stop posting now as I've had a ***** day, some beer and don't want to drag this thread down.

 

[Alex]

Haha - I'm in your gang. Eveything I own is breaking. I looked for a rope yesterday to hang myself......even that bloody broke!

 

[Jamesx19]

I think ndg has a point.

The system was originally all mild steel, which expands slightly less than Stainless (I looked at expansion tables but I stand to be corrected)

The helpful thing on stainless is the colouring at temperature. Certainly parts of the system reach at least 250°C looking at the stainless manifolds, cat pipes and inner part of the Dansk silencer.

Just watch an engine Dyno vid on YouTube to see an exhaust manifold glowing cherry red very quickly.

I've no doubt that Porsche put in a flexi for at least partly that reason and longevity of the system. ( And maybe other reasons)

I'm reviewing doing up everything tight as I wonder where will fatigue first! I suppose the thin plate that the silencers mount to flex a fair bit. Possibly they allow the movement necessary? Otherwise it'll be the slip joint between the silencers and Cat pipes.

 

[Alex]

As far as I know they were all stainless, they just look like mild steel after a few years. I know the original porsche manifolds are deffo stainless.

The flex thing is a red herring. The manifolds get hotter like you say but there's no flex between the cat and manifold and both are bolted to the block without any allowance for expansion.

 

[ndg]

Feeling much better today :wink:

I think the original systems are probably 410 and the Dansk will be something like 304 with co-efficients of expansion of 9.9 and 17 x10-6m/mC respectively.

The OE centre exhaust mount looks like is has a fixed tension clamp (wavy clamp in the picture below) fitted which would allow the pipes to move inside it axially.

 

[Alex]

Mine doesn't have those wavy clamps on. Solid on mine.


As seen here when I had my DANSK on:

 

[ndg]

Interesting, mine has nothing, so didn't even know they existed until last night!

 

[Alex]

Here's a better view of mine:

Both cat clamps bolt into the rear engine mount bracket: