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Old 11-29-2011, 08:54 PM   #1
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Default Dreaded Downpipe crack....

Hi Guys

I have my first evening (2-3 hours) track day in two days time and have just found a small crack in the down pipe ....about 4 inches from the turbo outlet.

I appreciate this needs to be fixed but my question is, will driving it like this cause any serious problems? (it doesn't appear to have yet...)

Also, is this the most likely cause of my hunting idle and flat spot on pressing the accelerator when starting from stopped.......? (eg. lights, give ways etc)

Cheers
Mark
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Old 11-29-2011, 09:11 PM   #2
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Originally Posted by mx5-kiwi View Post
I appreciate this needs to be fixed but my question is, will driving it like this cause any serious problems?
Assuming that it's not causing hot gas to spew onto something important (eg: your brake system) it's not going to cause anything cataclysmic. At cruise, the crack will likely admit a tiny amount of fresh air into the exhaust system, and as this is likely upstream of the O2 sensor, this will cause the sensor to read artificially lean, thus causing the engine to run somewhat rich.

Quote:
Also, is this the most likely cause of my hunting idle and flat spot on pressing the accelerator when starting from stopped.......? (eg. lights, give ways etc)
Could be. Depending on the severity, the aforementioned richness might be hurting you.
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Old 11-29-2011, 09:38 PM   #3
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Thanks Joe. I might get the crack welded temporarily and look at my options.

The muffler people say the exhaust heat wrap can contribute to this issue, anyone care to comment on that?
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Old 11-30-2011, 02:47 PM   #4
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Originally Posted by mx5-kiwi View Post
Thanks Joe. I might get the crack welded temporarily and look at my options.

The muffler people say the exhaust heat wrap can contribute to this issue, anyone care to comment on that?
There's an age old debate regarding this issue. I've seen it go both ways. The best prevention is to coat the wrap in the high temp silicone spray that DEI sells, and to make sure the pipe you're wrapping is not rusted to begin with and that there's no moisture on the piping before wrapping.

Usually though when the wrap causes failure it's usually by a flange, where the wrap ends and pipe is exposed. That exposed section of pipe radiates heat out from it's surface and is usually much cooler than the wrapped section of pipe next to it. That temperature differential can cause the welds and piping to anneal and eventually break.
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