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#2875118 - 01/18/13 09:07 AM Exhaust Flex Pipe--Why some have, others don't?
TallPaul Offline


Registered: 10/22/03
Posts: 12912
Loc: By Detroit
Out of the many vehicles I have owned, and the 5 currently in my driveway, only one came with an exhaust flex pipe. If the flex pipe is so important why don't all exhaust systems have one? What are the consequences of replacing a flex pipe with a straight piece of metal tubing? I think it all depends on how much give the hangers have.
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#2875127 - 01/18/13 09:15 AM Re: Exhaust Flex Pipe--Why some have, others don't? [Re: TallPaul]
HerrStig Offline


Registered: 08/24/11
Posts: 2929
Loc: Boston, MA
Transverse engines need them, RWD with "standard" mounting -- usually not.

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#2875134 - 01/18/13 09:21 AM Re: Exhaust Flex Pipe--Why some have, others don't? [Re: TallPaul]
eljefino Online   content


Registered: 06/15/03
Posts: 23779
Loc: ME
Cavalier OHV transverse has the spring loaded flange with asbestos-ey donut. The springs suspciously remind me of valve springs that didn't make the but for 5000 compressions a second. LOL

IMO a flexpipe is smoother inside.

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#2875143 - 01/18/13 09:28 AM Re: Exhaust Flex Pipe--Why some have, others don't? [Re: TallPaul]
Hokiefyd Offline


Registered: 06/24/04
Posts: 10959
Loc: North Carolina
Our Acura does have a flex pipe. The two sides of the exhaust from the V-6 come down to meet together at a y-pipe, then through a flex pipe, then to a third catalytic converter. The flex pipe absorbs fore-and-aft movements of the exhaust due to the engine rocking back and forth (transverse mounting).

Our Honda does not have a flex pipe. Fore-and-aft movements of the exhaust are taken up at the flange at the bottom of the exhaust manifold; there are two bolts (with springs) and it's sort of a "ball-and-socket" joint there. That joint has been problematic (with a TSB out to replace that donut gasket), and Honda changed the CR-V in 2010 to a design with a flex pipe.
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#2875151 - 01/18/13 09:30 AM Re: Exhaust Flex Pipe--Why some have, others don't? [Re: TallPaul]
Kruse Offline


Registered: 10/05/05
Posts: 3037
Loc: Kansas
Originally Posted By: TallPaul
Out of the many vehicles I have owned, and the 5 currently in my driveway, only one came with an exhaust flex pipe.


Did you or do you still own the (rear wheel drive, BTW) Aerostar? I've owned 4 of them and they came with the flex pipe. People on some of the Aerostar forums always said that a solid pipe would never last, so I've always put a flex pipe in as a replacement.

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#2875158 - 01/18/13 09:35 AM Re: Exhaust Flex Pipe--Why some have, others don't? [Re: TallPaul]
kschachn Offline


Registered: 12/26/05
Posts: 2485
Loc: Upper Midwest
My Accord has three spring/donut joints and one flex pipe. Plus two other joints that aren't flexible. I've never seen so many joints since college.
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#2875180 - 01/18/13 09:55 AM Re: Exhaust Flex Pipe--Why some have, others don't? [Re: Kruse]
TallPaul Offline


Registered: 10/22/03
Posts: 12912
Loc: By Detroit
Originally Posted By: Kruse
Originally Posted By: TallPaul
Out of the many vehicles I have owned, and the 5 currently in my driveway, only one came with an exhaust flex pipe.


Did you or do you still own the (rear wheel drive, BTW) Aerostar? I've owned 4 of them and they came with the flex pipe. People on some of the Aerostar forums always said that a solid pipe would never last, so I've always put a flex pipe in as a replacement.


Yes, the '92 Aerostar RWD 3.0 is the one. I had the flex pipe replaced about three years ago and it rotted already, so I just had a straight pipe installed. We hardly ever drive it anymore, 500 miles in last 6 months, so not sure we will see the adverse effects if any.

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#2875205 - 01/18/13 10:10 AM Re: Exhaust Flex Pipe--Why some have, others don't? [Re: kschachn]
scurvy Offline


Registered: 02/19/07
Posts: 2268
Loc: Chicago IL USA
Originally Posted By: kschachn
My Accord has three spring/donut joints and one flex pipe. Plus two other joints that aren't flexible. I've never seen so many joints since college.


LOL cheers

I see what you did there.
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#2875246 - 01/18/13 10:41 AM Re: Exhaust Flex Pipe--Why some have, others don't? [Re: TallPaul]
mcshooter Offline


Registered: 01/28/07
Posts: 277
Loc: ohio
the only cars i have had with aflex section were v6 engines that both front and rear pipes join into one exhaust.. a 4 cly did not have one .. a flex pipe i believe is used on a transverse mounted engine due to rubber engine mounts.. when the engine moves the exhaust has to go along


Edited by mcshooter (01/18/13 10:42 AM)

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#2875280 - 01/18/13 11:10 AM Re: Exhaust Flex Pipe--Why some have, others don't? [Re: TallPaul]
TallPaul Offline


Registered: 10/22/03
Posts: 12912
Loc: By Detroit
I can see where the transverse engine fwd cars need flex pipe, but maybe simpler to just exit the exhaust out the side by the front tire and skip the flex pipe. crzy
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"There is a slight vibration in it that I always attributed to something I can't explain." --Neil Young

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#2875291 - 01/18/13 11:17 AM Re: Exhaust Flex Pipe--Why some have, others don't? [Re: TallPaul]
Kestas Offline



Registered: 06/04/02
Posts: 10790
Loc: The Motor City
I imagine a big reason for going to flex pipes is to reduce noise, vibration, and harshness (NVH) in vehicles. Lots of manufacturing money is spent to reduce NVH.

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#2875301 - 01/18/13 11:22 AM Re: Exhaust Flex Pipe--Why some have, others don't? [Re: HerrStig]
440Magnum Offline


Registered: 02/01/09
Posts: 6216
Loc: Texas
Originally Posted By: HerrStig
Transverse engines need them, RWD with "standard" mounting -- usually not.


This. Transverse engines rock fore and aft and generally have mounts that allow a lot of movement to absorb vibrations from smaller engines, which makes the engine movement at right angles with the major axis of the exhaust pipe as it passes under the car. Either a ball-joint ("donut") or flex pipe is generally needed to allow enough range of motion.

Longitudinal (the RIGHT way ;-) ) engines rotate left/right under different loads, so they just tend to twist the exhaust pipe on its major axis. The engine mounts are ususally stiffer since rear-drive engines tend to be bigger v6 and v8 engines that don't shake as much. Compliant mountings in the exhaust hangers can usually absorb that movement so no flex pipe or donut is needed in most cases.

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#2875426 - 01/18/13 01:04 PM Re: Exhaust Flex Pipe--Why some have, others don't? [Re: Kestas]
kschachn Offline


Registered: 12/26/05
Posts: 2485
Loc: Upper Midwest
And that money carries over into replacement parts too. The difference between OEM and aftermarket flex pipes for the Accord is like night and day. If the pipe on my car hadn't been damaged it would probably still be good today. The Bosal replacement lasted about a year and a half, and was replaced with an OEM part which I don't anticipate wearing out before the whole car goes to the boneyard.

Originally Posted By: Kestas
I imagine a big reason for going to flex pipes is to reduce noise, vibration, and harshness (NVH) in vehicles. Lots of manufacturing money is spent to reduce NVH.


Edited by kschachn (01/18/13 01:05 PM)
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1994 BMW 530i, 188K
1996 Honda Accord, 201K
1999 Toyota Sienna, 302K
2000 Toyota ECHO, 223K

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#2876151 - 01/19/13 07:11 AM Re: Exhaust Flex Pipe--Why some have, others don't? [Re: TallPaul]
eljefino Online   content


Registered: 06/15/03
Posts: 23779
Loc: ME
^ Yeah I cheaped out and got an advance flexpipe that wasn't stainless like the OE saturn one. A year later it's rusty and creaks horribly when flexed-- I don't give it much more time. frown

Ironically, if I had bought a direct fit catalytic converter (that includes flexpipe and downpipe up to the manifold), it would (probably?) have come with a stainless flexpipe to meet the required 5 year warranty.

Coincidentally my whole exhaust hangs on these 3 inch long rubber hangers that let the whole system move an inch fore and aft. The flex lets the engine rotate but there's still this fore and aft to contend with.

OT It's not the most sophisticated engine in the world vibration wise and the soft mounts get on my nerves when I'm going through the gears and can feel it bouncing around up there.

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#2876477 - 01/19/13 02:02 PM Re: Exhaust Flex Pipe--Why some have, others don't? [Re: eljefino]
kschachn Offline


Registered: 12/26/05
Posts: 2485
Loc: Upper Midwest
Oh yeah, I forgot about those things, in addition to everything else I noted on my Accord exhaust I have eight of those rubber things too.

Like everything else Honda though, it works and works well. Sometimes seems weird compared to my Toyota but it gets the job done and never seems to fail (on its own).

Originally Posted By: eljefino
Coincidentally my whole exhaust hangs on these 3 inch long rubber hangers that let the whole system move an inch fore and aft. The flex lets the engine rotate but there's still this fore and aft to contend with.
_________________________
1994 BMW 530i, 188K
1996 Honda Accord, 201K
1999 Toyota Sienna, 302K
2000 Toyota ECHO, 223K

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