Birty Dastards Jeep Club

Tech Forum => Workshop => Topic started by: Jeepthang on April 10, 2008, 07:53:25 PM

Title: Exhaust question
Post by: Jeepthang on April 10, 2008, 07:53:25 PM
I've got a 99 XJ. Does anybody know whether, from a legal perspective, the exhaust tailpipe must be located by the outside confines of the vehicle?

The reason I'm asking is that I need to reroute or shorten my tailpipe (because it's currently sandwiched between the fuel tank skid and the leaf hanger) and I'm thinking of shortening it so that it "ejects" downward just after the rear axle and about 2" before the fuel tank. It's an idea I got from a US forum.

The fuel tank skid will act as a heat shield but I'm wondering legally where I stand with a tailpipe that "ejects" 3/4's of the way down the underside of the vehicle.

Has anybody else had similer problems after fitting a fuel tank skid?

All thoughts gratefully received!!  :-D
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Post by: isle of man on April 10, 2008, 08:08:49 PM
i had the same problem................forever catching the foooooooker, in the end i cut it off just after the belly pan and left it pointing down.

(http://http://snap32.photobox.co.uk/918360195b8f820e9d184c20584d32d44ce352aee8841195c877d990.jpg)

cut it on the bend above - never had a problem since.
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Post by: wazza on April 10, 2008, 10:52:00 PM
thats exactly what i did!

i think its down to the discression of the motist an the traffic plod might not be happy if you ever got random stopped an checked.

i chopped mine right through the last bit of the bend as it started to point to the rear of the vehicle after the axle.

im sure there is something saying they have to exit outside of the vehicle and not under, as the exhaust gasses could get into the car.
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Post by: Jeepthang on April 10, 2008, 11:25:13 PM
Quote from: "wazza"
i chopped mine right through the last bit of the bend as it started to point to the rear of the vehicle after the axle.


That's exactly where in planing to chop mine. Great stuff, the grinder will be out on Saturday!

Thanks guys
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Post by: greggmo on April 10, 2008, 11:47:04 PM
the only reason an exaust exits at the tail is to stop dangerous fumes getting inside the vehichle. cutting it short might cause this to happen but you will soon know or fall asleep and never know :lol:
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Post by: isle of man on April 11, 2008, 12:28:53 AM
when the exhaust catalyst was fitted - that was supposed to stop the carbon monoxide.
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Post by: Dave69 on April 11, 2008, 01:54:06 PM
who have you been talking to ???

as long as the pipe exits the side or rear of the vehicle there shouldn't be a problem. just left open under the car could result in fumes making their way into the car which TBH doesn't smell nice
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Post by: Jeepthang on April 12, 2008, 12:56:27 AM
Quote from: "Dave69"
who have you been talking to ???

as long as the pipe exits the side or rear of the vehicle there shouldn't be a problem. just left open under the car could result in fumes making their way into the car which TBH doesn't smell nice


This is my issue. I don't want the tailpipe to exit the side or the rear of the vehicle. I planning tomorrow to cut it off just after the rear axle. It'll the pointing downwards so to avoid the gas tank (even though the skid will act as a heat shield) and will "exit" directly under the car.

How are the fumes going to make their way into the XJ? Has anybody else experienced "smells" etc. post doing this?
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Post by: Dave69 on April 12, 2008, 09:43:50 AM
the problem with the pipe exiting the vehicle underneath there is no smooth air to take the gasses away from the vehile. exiting under the car you would have thought the same but it is not always the case. airflow under the car is turbulant and this causes negative flow and dead air pockets which fumes can get caught in. Even with modern build technologies car building doesn't create a full sealed car, if this was the case you couldn't shut the doors due to the pressure difference. So what manufacturers do is put pressure vents in the rear of the car and alos the body pannels are only partially sealed by mastic, if they sealed all the panels then the cost would go up and the track worker would have to do more work. All these little build issues create gaps which allow gases to creep into the car interior. It just might not be an issue but once the smell of exhaust gasses start to enter the car your always then driving with the window open.

The final choice is yours, or buy some pipe form milner off road and make a bespoke slip on pipe to send it where you actually need it after you have cut the origional part off
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Post by: greggmo on April 12, 2008, 10:43:15 AM
the thing to do is try it i guess. if it is no good weld the peice back on and go back to the drawing board. 8-)
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Post by: Dave69 on April 12, 2008, 11:51:03 AM
as above but you depends on where you cut the pipe you might want to get one of the end pipe sleeves to direct the gasses to the ground if you have issues
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Post by: wazza on April 12, 2008, 12:25:09 PM
well i cut mine in the same place an it was fine, never had the slightest wiff of fumes.

you'll only be cutting, a max of 2foot off the end. With the pressure so much on leaving the pipes, it gets directed staright out the back of the car anyway,

if you leave it staright out the back you've got more chance of bending it in the same place as you catch it when reversing over something.
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Post by: Bubba on April 12, 2008, 12:40:54 PM
PUT A TRACTOR ONE UP THROUGH YA BONNET NO PROBS WITH FUMES THEN
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Post by: Tragic on April 12, 2008, 03:45:36 PM
Quote from: "isle of man"
i had the same problem................forever catching the foooooooker, in the end i cut it off just after the belly pan and left it pointing down.

(http://http://snap32.photobox.co.uk/918360195b8f820e9d184c20584d32d44ce352aee8841195c877d990.jpg)

cut it on the bend above - never had a problem since.



Peter, am I right in thinking that's the cat you can see above the skidplate? Or do you have a cat further upstream and that is a muffler?
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Post by: isle of man on April 12, 2008, 07:09:08 PM
the cat is further up-stream that muffler is a http://http://www.spintechmufflers.com/spintech/spintechindex.asp