Automotive

OK to Replace Exhaust Flex Pipe with rigid Straight Pipe?

  • Last Updated:
  • May 15th, 2019 7:37 pm
[OP]
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Apr 29, 2010
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London

OK to Replace Exhaust Flex Pipe with rigid Straight Pipe?

I have an older vehicle (Nissan Quest) which makes use of an exhaust flex pipe right after the cat converter. Despite replacing the flex pipe 3 months ago due to a horrible sound coming from the old flex pipe, the new pipe has begun making noises.

Is there any issue with replacing the flex pipe with a rigid straight pipe? None of my other vehicles appear to use a flex pipe so why does the Nissan Quest need one?

Thanks.
19 replies
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Jul 26, 2007
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rosario99 wrote: I have an older vehicle (Nissan Quest) which makes use of an exhaust flex pipe right after the cat converter. Despite replacing the flex pipe 3 months ago due to a horrible sound coming from the old flex pipe, the new pipe has begun making noises.

Is there any issue with replacing the flex pipe with a rigid straight pipe? None of my other vehicles appear to use a flex pipe so why does the Nissan Quest need one?

Thanks.
Lot of other cars has flex pipe for engine vibration and movement during operation. Your V6 in tour quest may move more then your other engines in other cars. You can try putting a test pipe, but you might return due to constant rattling in the exhaust system.
[OP]
Sr. Member
Apr 29, 2010
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London
peteryorkuca wrote: Lot of other cars has flex pipe for engine vibration and movement during operation. Your V6 in tour quest may move more then your other engines in other cars. You can try putting a test pipe, but you might return due to constant rattling in the exhaust system.
Good idea. I will give it a try and if an issue will return and leave it at that.

Thanks
Deal Addict
Sep 8, 2017
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You need the flex pipe. The engine moves but the exhaust doesn't. A straight piece of pipe will break something else as the engine tries to move.

The new pipe is making noise because I assume you had a new flex pipe welded to old, rusty exhaust pipe. And now it's leaking.

You probably need to replace the entire front pipe assembly.

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Modern vehicles have unnecessary cost squeezed out through value engineering - if it was not needed it would not be there.
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Likely bad motor mounts causing premature wear on the flex pipe or the new flex pipe was the wrong one

If you bypass the flex with a straight pipe, the rocking motion will be transferred to the weakest spot. All that’s going to happen is either tear the header pipes off the exhaust manifold flanges or rip the exhaust pipe out of the front of the muffler,
Deal Addict
Apr 6, 2008
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I would take the vehicle into a custom exhaust shop (not a parts swapper like Canadian Tire) and have quote to REPAIR the exhaust. A good shop can do small fixes that are reasonable yet solve the problem without buying expensive replacement parts. I always do this on old vehicles that need a cheap fix to last a few years.
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Jun 26, 2007
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No, never replace a flex pipe with a solid pipe. The reason some cars have a flex pipe and others don’t comes down to the material used to make the exhaust and engine position and vibration from the engine. If you put something solid there, it’s only a matter of time before the exhaust falls into pieces and the exhaust starts to accrue holes throughout.
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rosario99 wrote: I have an older vehicle (Nissan Quest) which makes use of an exhaust flex pipe right after the cat converter. Despite replacing the flex pipe 3 months ago due to a horrible sound coming from the old flex pipe, the new pipe has begun making noises.

Is there any issue with replacing the flex pipe with a rigid straight pipe? None of my other vehicles appear to use a flex pipe so why does the Nissan Quest need one?

Thanks.
What "noise" would be coming from the flex pipe? Exhaust noise? Perhaps the connections have come loose or were not properly fastened in the first place or gaskets or sealant is missing?
The flex pipe is necessary to isolate a moving part from the rigidly mounted part. A straight pipe will only damage both parts.
Martin (deal addict) wrote: Modern vehicles have unnecessary cost squeezed out through value engineering - if it was not needed it would not be there.
You make absolutely no sense at all.
The Government cannot give to anybody anything that the Government does not first take from somebody else.
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Martin (deal addict) wrote: Maybe to another engineer.
No, to no one.
Your " unnecessary cost squeezed out through value engineering" statement is nonsense.
There is no "unnecessary cost squeezed out" in a flex pipe. It is there for a very good reason, to isolate vibrations and movement.......nor to squeeze cost or a value engineering requirements.
The Government cannot give to anybody anything that the Government does not first take from somebody else.
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Martin (deal addict) wrote: Modern vehicles have unnecessary cost squeezed out through value engineering - if it was not needed it would not be there.
I’ve never had to deal with any exhaust issues on my 10yr + Honda, Acura, Toyota’s. A $200 muffler on an 2010 Jeep is about it. Whereas I remember in the 80’s having to deal with exhaust issues every few years on various vehicles. Maybe I’ve been lucky recently?
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Pete_Coach wrote: No, to no one.
Your " unnecessary cost squeezed out through value engineering" statement is nonsense.
There is no "unnecessary cost squeezed out" in a flex pipe. It is there for a very good reason, to isolate vibrations and movement.......nor to squeeze cost or a value engineering requirements.
You have misunderstood what I was saying and I am not in the teaching business.
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cartfan123 wrote: I’ve never had to deal with any exhaust issues on my 10yr + Honda, Acura, Toyota’s. A $200 muffler on an 2010 Jeep is about it. Whereas I remember in the 80’s having to deal with exhaust issues every few years on various vehicles. Maybe I’ve been lucky recently?
The point I was making is that a section of braided flexible pipe is more expensive than solid. The manufacturer has decided it is essential otherwise they would have gone with a cheaper option. The exercise of working through designs identifying and eliminating unnecessary cost and looking for cheaper alternative solutions is called value engineering. I would therefore not replace the flexible section with a solid section or problems will undoubtedly ensue.
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Martin (deal addict) wrote: You have misunderstood what I was saying and I am not in the teaching business.
What's to teach. You make no sense.
Nothing about a flex pipe has "unnecessary cost squeezed out through value engineering " but you are very correct that "if it was not needed it would not be there. "
The flex pipe is a engineered solution to a problem....not unnecessary and not a value engineering issue either. x
The Government cannot give to anybody anything that the Government does not first take from somebody else.
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Pete_Coach wrote: No, to no one.
You should not speak on behalf of everyone in terms of what people can and can't understand. You don`t understand as demonstrated by your repetitive posts and I am happy to leave it there.
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Martin (deal addict) wrote: You should not speak on behalf of everyone in terms of what people can and can't understand. You don`t understand as demonstrated by your repetitive posts and I am happy to leave it there.
I am very familiar with value engineering and where and why it is used. In aviation (which was my primary business for decades) value engineering is always in conflict with safety and reliability.
You made a broad statement that has no explanation nor applicability to the topic. As an engineer (if that is what you claim to be), it is not acceptable to make incomplete and irrelevant statements.
The Government cannot give to anybody anything that the Government does not first take from somebody else.
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Pete_Coach wrote: value engineering is always in conflict with safety and reliability.
Whatever you say. You win.
Last edited by Bevatron on May 14th, 2019 9:43 am, edited 1 time in total.
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cartfan123 wrote: I’ve never had to deal with any exhaust issues on my 10yr + Honda, Acura, Toyota’s. A $200 muffler on an 2010 Jeep is about it. Whereas I remember in the 80’s having to deal with exhaust issues every few years on various vehicles. Maybe I’ve been lucky recently?
Exhausts tend to be made of better materials now (409 stainless steel) vs before (aluminized steel and galvanized steel). I personally think it’s because Chinese steel/ parts have drastically decreased the cost of stainless steel components vs years back. Another example is the low cost and widespread availability of cheap stainless steel Chinese bbqs

409 stainless has 2-3x the corrosion resistance of galvanized steel. Aluminized steel is about 1.5 x more corrosion resistant than galvanized steel

FWD with transverse mounted engines tend to have flex pipes to account for engine rotational movement (twisting) which otherwise would need the exhaust pipe to expand/ contract in length

RWD with longitudinal mounted engines tend not to have flex pipes because the twisting motion is along the exhaust pipe
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Feb 6, 2011
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You can install a straight pipe as long as you weld in a bell flare with spring loaded bolts and a donut gasket to allow flexing. I've done it before, it will last a long time without breaking anything else.

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