building a custom 3" system, need some advice

609 Views 10 Replies 4 Participants Last post by Cypher2k, Nov 28, 2001

Cypher2k

Discussion Starter · Nov 27, 2001

Ive got a local tuner who can make me a custom turboback system fairly cheaply. I wanted to bounce some of the design ideas off you guys.
The downpipe would come down and go horizontal. With a flex peice at the end paralell to the ground. The stock cat would be cut back at both ends until the inlet and outlet are 3", then basic 3" piping back to whatever muffler I chose...

Speaking of this. Whats a nice quiet stainless muffler?

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DaBlackJetta

· #2 · Nov 27, 2001

Re: building a custom 3" system, need some advice (Cypher2k)

quote:[HR][/HR]The downpipe would come down and go horizontal. With a flex peice at the end paralell to the ground.[HR][/HR]

No, the flex tube should be right after the turbo to eliminate the DP from hitting the steering rack.

quote:[HR][/HR] The stock cat would be cut back at both ends until the inlet and outlet are 3", then basic 3" piping back to whatever muffler I chose...[HR][/HR]

Nope again.. you will fail the cat in about 3K miles it you do it this way...

quote:[HR][/HR]Speaking of this. Whats a nice quiet stainless muffler?[HR][/HR]

In 3"? We make one. Order with the dual 2.5" tip for either the stock valance or the 4 motion valance.

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flanders

· #3 · Nov 27, 2001

Re: building a custom 3" system, need some advice (DaBlackJetta)

can you purchase a 3" high-flo cat from somewhere (not with a dp?)

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Cypher2k

Discussion Starter · #4 · Nov 27, 2001

Re: building a custom 3" system, need some advice (flanders)

Why would the stock cat fail?
The flex piece on the DP... Im told the little short ones dont last very long...
Thats why Tapp wants to build one with the flex closer to the cat. As it turns out, looking a lot like this Chris Green thing: http://forums.vwvortex.com/zerothread?id=161432
I hear you about the possibility of it hitting. Id rather have it flexing closer to the engine so that the whole DP is not moving back and forth. But if the aforementioned DP is not hitting... Its tough.
And how much are high flow cats running for anyhow?

[Modified by Cypher2k, 11:04 AM 11-27-2001]

[Modified by Cypher2k, 11:05 AM 11-27-2001]

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DaBlackJetta

· #5 · Nov 27, 2001

Re: building a custom 3" system, need some advice (Cypher2k)

Flex tubes come in all different sizes and flavors. I source a really high quality unit that is designed to deal with the heat range and flexibility that we have seen on stock 1.8T engines under throttle. I could have gone cheaper, but I don't want failures. A hint to the kind of flex tube you using is this: the flex tubes that have stainless braiding over are ususally designed for higher temps, but low flexibility. They are designed to be used in factories where steam (or other high temp, hi pressure fluids) need to be guided into a place that would be too expensive to run normal tubing. They are designed to flex once and stay in the position.. not flex multiple times.
Also, I can only theorize on why stock cats fail when subjected to a 3" DP. My theory is that the stock cat cannot handle the amount of flow a 3" DP is able to give.
This is what my stock cat looked like after 3K of useage while sitting downstream of a 3" DP:

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flanders

· #6 · Nov 28, 2001

Re: building a custom 3" system, need some advice (DaBlackJetta)

I love that cat pic

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Cypher2k

Discussion Starter · #7 · Nov 28, 2001

Re: building a custom 3" system, need some advice (flanders)

The guy at Tapp theorized that you might have been running rich. He doesnt agree that increased flow alone could cause that cat to fail.
So im at a loss as to what to do about this.

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jim wilson

· #8 · Nov 28, 2001

Re: building a custom 3" system, need some advice (Cypher2k)

I hope you're not talking about Tap from florida. Turbo cars do run rich, even richer with some chips.

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Cypher2k

Discussion Starter · #9 · Nov 28, 2001

Re: building a custom 3" system, need some advice (jim wilson)

tapp from ottawa.

But tell me more.

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jim wilson

· #10 · Nov 28, 2001

Re: building a custom 3" system, need some advice (Cypher2k)

not much to tell, the richer you are the faster the cat melts unless it's large to absorb enough heat so that it doesn't melt and can cool off before the next rich run cycle

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Cypher2k

Discussion Starter · #11 · Nov 28, 2001

Re: building a custom 3" system, need some advice (jim wilson)

Ok. This doesnt really explain why a less restrictive downpipe and exaust would cause the engine to run richer. And thus burn out the cat.

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