[GasTungstenArc]

I am preparing our Astro for a trip from Ohio to Florida and back in a couple of weeks. Last Saturday's projects were new Gas-A-Just shocks front and rear and some theft prevention on the catalytic converter.

When I got under the van to work with the cat, I found that the Y-pipe had a longitudinal split about 2" long just downstream from the collection point. I welded it shut, but I wonder if others here have experienced a split in that area of the Y-pipe. I can't help but wonder if the catalyst might be plugged up, causing excessive backpressure, leading to the split as a stress relief.

 

[AstroWill]

I couldn't imagine backpressure being able to do that.

 

[Sailing_Faith]

I suspect that the split came from a persistent misfire loading up the exhaust….
You will soon know if the cat is clogged… lack of power should be evident if it is.

 

[GasTungstenArc]

I couldn't imagine backpressure being able to do that.

I wouldn't think so, either. Taken out of that environment, a 16ga steel tube should be able to hold several hundred PSI. Add age, corrosion, heat, and vibration in, and I'm sure it's a lot less, but still should be strong enough. Exhaust pressure can only build so much anyway; when the exhaust valve opens, exhaust normally flows out because that's the direction of the gradient. Build enough pressure downstream of the exhaust valve, and the gradient inclines the other way.

 

[GasTungstenArc]

I suspect that the split came from a persistent misfire loading up the exhaust….
You will soon know if the cat is clogged… lack of power should be evident if it is.

As far as power is concerned, I don't really know what to expect from this van, but it feels like I'm getting the 150-180HP that it should have. But...the cat is now in, let's say, "storage configuration," so backpressure and power loss shouldn't be an issue.

 

[M_a_t_t]

I think you would know if you had a clogged cat. I bought a van with a clogged cat and it wouldn't go past 13 mph because it couldn't push the exhaust out of the engine as fast as it needed.

 

[markmitch]

Most GM Y pipes are double walled steel, Was the crack all the way through and was it leaking?

 

[GasTungstenArc]

Most GM Y pipes are double walled steel, Was the crack all the way through and was it leaking?

I suppose I can't say. I didn't try poking anything through it and I didn't try to look inside. I also can't say whether I remember seeing soot on the outside around the split. I saw it and welded it up. It still has plenty of exhaust leaks at probably both ends of the manifolds, so I can't say whether I made it any quieter either.

 

[markmitch]

Understood, the only real reason I even know this is because I had one split on an Astro a long time ago and the split didn't leak but it would not pass state safety inspection with a split in it, And when I went to buy one I was told it was pretty common on many GM vehicles for them to split. Something due to the manufacturing process with it being double walled..

 

[GasTungstenArc]

Understood, the only real reason I even know this is because I had one split on an Astro a long time ago and the split didn't leak but it would not pass state safety inspection with a split in it, And when I went to buy one I was told it was pretty common on many GM vehicles for them to split. Something due to the manufacturing process with it being double walled..

Very interesting. I wonder why they bothered with double wall. I know why it's done on motorcycles, but the same reasons don't apply here.

 

[AstroWill]

I never noticed, all exhaust work I have done has been single wall. Wouldn't make any sense for them to use double wall, at all on our vans. Have any pictures of this?

 

[markmitch]

No I do not, but It was also posted on TBI chips.com as a reason not to use the stock Y pipe if you're looking for performance gains since the double wall makes the inside pipe tiny in comparison to the outside pipe.

 

[AstroWill]

Got a link?

 

[opelbits]

I had headpipe ony Opel Manta split. I had just exited the highway. Pipe was nice and hot and I hit a big standing pool of water on a sub 35* day. Hot pipe plus nearly freezing water...