bowgus

Yeah ... I'd also like to know , first of all how "cold air", or any air for
that matter, could possibly enter a (pressurized by the engine firing)
exhaust manifold ... geez .. that's like saying cold air can enter via the
tailpipe, make it's way through the exhaust sytem to the exhaust manifold
wher it will ... and this I'd really like to understand ... damage "the
valves". Now, in my youth I have reduced back pressure on a few autos and
run them hard thereby burning exhaust valves ... maybe this is what you are
thinking? Or maybe you are thinking that the O2 sensor might somehow be
misled by the cracked manifold thereby changing the mixture? Look there is
no argument here ... just a question as to how this works ... I am always
eager to learn more about the jeep ...


"Jerry Bransford" <jerrypb@mecox.net> wrote in message
news:CUaTb.3858$1O.2264@fed1read05...
> "Irish Redneck" <seeayeemm@hotmail.com> wrote in message
> news:opr2pb0bviy2qpcc@netnews.insightbb.com...
> > On Sun, 1 Feb 2004 08:15:19 -0800, Jerry Bransford <jerrypb@mecox.net>
> > wrote:
> >
> > > A cracked exhaust header should be replaced since it can damage the
> > > valves
> > > by letting cold air in through the crack.
> > >
> >
> > please explain to me the science behind this 'fact'.
>
> Do your own research if you want to argue against what I said that I stand
> behind...which on the surface sure seems like is you're itching to do.
>
> --
> Jerry Bransford
> To email, remove 'me' from my email address
> N6TAY, PP-ASEL
> See the Geezer Jeep at
> http://members.***.net/jerrypb/
>
>

bowgus

Yeah ... I'd also like to know , first of all how "cold air", or any air for
that matter, could possibly enter a (pressurized by the engine firing)
exhaust manifold ... geez .. that's like saying cold air can enter via the
tailpipe, make it's way through the exhaust sytem to the exhaust manifold
wher it will ... and this I'd really like to understand ... damage "the
valves". Now, in my youth I have reduced back pressure on a few autos and
run them hard thereby burning exhaust valves ... maybe this is what you are
thinking? Or maybe you are thinking that the O2 sensor might somehow be
misled by the cracked manifold thereby changing the mixture? Look there is
no argument here ... just a question as to how this works ... I am always
eager to learn more about the jeep ...


"Jerry Bransford" <jerrypb@mecox.net> wrote in message
news:CUaTb.3858$1O.2264@fed1read05...
> "Irish Redneck" <seeayeemm@hotmail.com> wrote in message
> news:opr2pb0bviy2qpcc@netnews.insightbb.com...
> > On Sun, 1 Feb 2004 08:15:19 -0800, Jerry Bransford <jerrypb@mecox.net>
> > wrote:
> >
> > > A cracked exhaust header should be replaced since it can damage the
> > > valves
> > > by letting cold air in through the crack.
> > >
> >
> > please explain to me the science behind this 'fact'.
>
> Do your own research if you want to argue against what I said that I stand
> behind...which on the surface sure seems like is you're itching to do.
>
> --
> Jerry Bransford
> To email, remove 'me' from my email address
> N6TAY, PP-ASEL
> See the Geezer Jeep at
> http://members.***.net/jerrypb/
>
>

bowgus

Yeah ... I'd also like to know , first of all how "cold air", or any air for
that matter, could possibly enter a (pressurized by the engine firing)
exhaust manifold ... geez .. that's like saying cold air can enter via the
tailpipe, make it's way through the exhaust sytem to the exhaust manifold
wher it will ... and this I'd really like to understand ... damage "the
valves". Now, in my youth I have reduced back pressure on a few autos and
run them hard thereby burning exhaust valves ... maybe this is what you are
thinking? Or maybe you are thinking that the O2 sensor might somehow be
misled by the cracked manifold thereby changing the mixture? Look there is
no argument here ... just a question as to how this works ... I am always
eager to learn more about the jeep ...


"Jerry Bransford" <jerrypb@mecox.net> wrote in message
news:CUaTb.3858$1O.2264@fed1read05...
> "Irish Redneck" <seeayeemm@hotmail.com> wrote in message
> news:opr2pb0bviy2qpcc@netnews.insightbb.com...
> > On Sun, 1 Feb 2004 08:15:19 -0800, Jerry Bransford <jerrypb@mecox.net>
> > wrote:
> >
> > > A cracked exhaust header should be replaced since it can damage the
> > > valves
> > > by letting cold air in through the crack.
> > >
> >
> > please explain to me the science behind this 'fact'.
>
> Do your own research if you want to argue against what I said that I stand
> behind...which on the surface sure seems like is you're itching to do.
>
> --
> Jerry Bransford
> To email, remove 'me' from my email address
> N6TAY, PP-ASEL
> See the Geezer Jeep at
> http://members.***.net/jerrypb/
>
>

DougW

bowgus did pass the time by typing:
> Yeah ... I'd also like to know , first of all how "cold air", or any air for
> that matter, could possibly enter a (pressurized by the engine firing)
> exhaust manifold ... geez .. that's like saying cold air can enter via the
> tailpipe, make it's way through the exhaust sytem to the exhaust manifold
> wher it will ... and this I'd really like to understand ... damage "the
> valves". Now, in my youth I have reduced back pressure on a few autos and
> run them hard thereby burning exhaust valves ... maybe this is what you are
> thinking? Or maybe you are thinking that the O2 sensor might somehow be
> misled by the cracked manifold thereby changing the mixture? Look there is
> no argument here ... just a question as to how this works ... I am always
> eager to learn more about the jeep ...

Think of it this way. Each time one of the cylinders exhausts it sends a
pulse through the pipe. All those pulses merge at the collector and form
a flow of exhaust all the way to the tailpipe. Once flowing, exhaust like
any fluid has a mass. In other words the flow wants to continue to move in
the direction it is moving. This is also why having a huge 3" exhaust pipe
can hurt. The flow becomes too slow and you loose any scavenging effects.
Larger pipes do not equal more power.

Since the exhaust pulses stop/start they also form a slight vacuum behind
the pulse. That is where air can get into the manifold. Air getting in
fools the O2 sensor into thinking your running too lean, then bad-things happen.

Sounds wonky doesn't it? :/ Leaks past the collector don't tend to suck
much if any air into the system, leaks at the exhaust flange cause the
most problems.

--
DougW

DougW

bowgus did pass the time by typing:
> Yeah ... I'd also like to know , first of all how "cold air", or any air for
> that matter, could possibly enter a (pressurized by the engine firing)
> exhaust manifold ... geez .. that's like saying cold air can enter via the
> tailpipe, make it's way through the exhaust sytem to the exhaust manifold
> wher it will ... and this I'd really like to understand ... damage "the
> valves". Now, in my youth I have reduced back pressure on a few autos and
> run them hard thereby burning exhaust valves ... maybe this is what you are
> thinking? Or maybe you are thinking that the O2 sensor might somehow be
> misled by the cracked manifold thereby changing the mixture? Look there is
> no argument here ... just a question as to how this works ... I am always
> eager to learn more about the jeep ...

Think of it this way. Each time one of the cylinders exhausts it sends a
pulse through the pipe. All those pulses merge at the collector and form
a flow of exhaust all the way to the tailpipe. Once flowing, exhaust like
any fluid has a mass. In other words the flow wants to continue to move in
the direction it is moving. This is also why having a huge 3" exhaust pipe
can hurt. The flow becomes too slow and you loose any scavenging effects.
Larger pipes do not equal more power.

Since the exhaust pulses stop/start they also form a slight vacuum behind
the pulse. That is where air can get into the manifold. Air getting in
fools the O2 sensor into thinking your running too lean, then bad-things happen.

Sounds wonky doesn't it? :/ Leaks past the collector don't tend to suck
much if any air into the system, leaks at the exhaust flange cause the
most problems.

--
DougW

DougW

bowgus did pass the time by typing:
> Yeah ... I'd also like to know , first of all how "cold air", or any air for
> that matter, could possibly enter a (pressurized by the engine firing)
> exhaust manifold ... geez .. that's like saying cold air can enter via the
> tailpipe, make it's way through the exhaust sytem to the exhaust manifold
> wher it will ... and this I'd really like to understand ... damage "the
> valves". Now, in my youth I have reduced back pressure on a few autos and
> run them hard thereby burning exhaust valves ... maybe this is what you are
> thinking? Or maybe you are thinking that the O2 sensor might somehow be
> misled by the cracked manifold thereby changing the mixture? Look there is
> no argument here ... just a question as to how this works ... I am always
> eager to learn more about the jeep ...

Think of it this way. Each time one of the cylinders exhausts it sends a
pulse through the pipe. All those pulses merge at the collector and form
a flow of exhaust all the way to the tailpipe. Once flowing, exhaust like
any fluid has a mass. In other words the flow wants to continue to move in
the direction it is moving. This is also why having a huge 3" exhaust pipe
can hurt. The flow becomes too slow and you loose any scavenging effects.
Larger pipes do not equal more power.

Since the exhaust pulses stop/start they also form a slight vacuum behind
the pulse. That is where air can get into the manifold. Air getting in
fools the O2 sensor into thinking your running too lean, then bad-things happen.

Sounds wonky doesn't it? :/ Leaks past the collector don't tend to suck
much if any air into the system, leaks at the exhaust flange cause the
most problems.

--
DougW

David C. Moller

I let mine go on WAY too long:
http://home1.gte.net/res0p2es/david/Manifold%201.jpg
http://home1.gte.net/res0p2es/david/Manifold%202.jpg

As Jerry mentioned, yes, it can cause damage (especially if it is as
bad as mine was). I *think* this is because a crack that far up the
exhaust manifold/header (like in the second picture) creates a sort of
vacuum leak, allowing too much air into the mixture, and causes
excessive heat. Not sure of the specific details on this, but people
whose opinions I trust/respect have told me this is 'bad and may cause
damage', and I believe them. :)
Not sure if I did cause any damage by letting mine deteriorate for so
long, but everything *seems* to be fine. If your crack is further down
the pipes (like in the first picture), closer to the collector area
where all the pipes converge, I doubt you have much to worry about
hurting anything at this time.

As for replacement, I found a Thorley header at a price too good to
pass up (I was originally looking at Borla), so I bought it and my
neighbor and I slapped it on. And ya, the 91-99 years sound right... I
remember worrying about that when mine arrived and I took a look at
the specifications sheet that shipped with it. But it fit like a
champ. Not sure about the auto tranny routing, never dealt with one.

Dave
http://mysite.verizon.net/res0p2es/david/index.htm

On Sun, 01 Feb 2004 15:27:05 GMT, "Harkin Banks" <ntwk_eng@yahoo.com>
wrote:

>Other than noise, is there any harm in letting this go unfixed for an
>extended period of time? Can it do damage to the block by not getting the
>heat out propoerly? Possible stupid questions but I had to ask.
>
>I have seen that most of the headers are made for manual transmission and
>that they will need some 'special routing' for auto trannies. I had the rest
>of the exhaust replaced (with standard parts, not cat-back system) a while
>back and am curious if this re-routing would require me to redo it again?
>
>At 4WD.com., the replacement manifold that they show is listed for years
>'91 - '99. Does this seem
>correct?
>
>Thanks.
>

David C. Moller

I let mine go on WAY too long:
http://home1.gte.net/res0p2es/david/Manifold%201.jpg
http://home1.gte.net/res0p2es/david/Manifold%202.jpg

As Jerry mentioned, yes, it can cause damage (especially if it is as
bad as mine was). I *think* this is because a crack that far up the
exhaust manifold/header (like in the second picture) creates a sort of
vacuum leak, allowing too much air into the mixture, and causes
excessive heat. Not sure of the specific details on this, but people
whose opinions I trust/respect have told me this is 'bad and may cause
damage', and I believe them. :)
Not sure if I did cause any damage by letting mine deteriorate for so
long, but everything *seems* to be fine. If your crack is further down
the pipes (like in the first picture), closer to the collector area
where all the pipes converge, I doubt you have much to worry about
hurting anything at this time.

As for replacement, I found a Thorley header at a price too good to
pass up (I was originally looking at Borla), so I bought it and my
neighbor and I slapped it on. And ya, the 91-99 years sound right... I
remember worrying about that when mine arrived and I took a look at
the specifications sheet that shipped with it. But it fit like a
champ. Not sure about the auto tranny routing, never dealt with one.

Dave
http://mysite.verizon.net/res0p2es/david/index.htm

On Sun, 01 Feb 2004 15:27:05 GMT, "Harkin Banks" <ntwk_eng@yahoo.com>
wrote:

>Other than noise, is there any harm in letting this go unfixed for an
>extended period of time? Can it do damage to the block by not getting the
>heat out propoerly? Possible stupid questions but I had to ask.
>
>I have seen that most of the headers are made for manual transmission and
>that they will need some 'special routing' for auto trannies. I had the rest
>of the exhaust replaced (with standard parts, not cat-back system) a while
>back and am curious if this re-routing would require me to redo it again?
>
>At 4WD.com., the replacement manifold that they show is listed for years
>'91 - '99. Does this seem
>correct?
>
>Thanks.
>

David C. Moller

I let mine go on WAY too long:
http://home1.gte.net/res0p2es/david/Manifold%201.jpg
http://home1.gte.net/res0p2es/david/Manifold%202.jpg

As Jerry mentioned, yes, it can cause damage (especially if it is as
bad as mine was). I *think* this is because a crack that far up the
exhaust manifold/header (like in the second picture) creates a sort of
vacuum leak, allowing too much air into the mixture, and causes
excessive heat. Not sure of the specific details on this, but people
whose opinions I trust/respect have told me this is 'bad and may cause
damage', and I believe them. :)
Not sure if I did cause any damage by letting mine deteriorate for so
long, but everything *seems* to be fine. If your crack is further down
the pipes (like in the first picture), closer to the collector area
where all the pipes converge, I doubt you have much to worry about
hurting anything at this time.

As for replacement, I found a Thorley header at a price too good to
pass up (I was originally looking at Borla), so I bought it and my
neighbor and I slapped it on. And ya, the 91-99 years sound right... I
remember worrying about that when mine arrived and I took a look at
the specifications sheet that shipped with it. But it fit like a
champ. Not sure about the auto tranny routing, never dealt with one.

Dave
http://mysite.verizon.net/res0p2es/david/index.htm

On Sun, 01 Feb 2004 15:27:05 GMT, "Harkin Banks" <ntwk_eng@yahoo.com>
wrote:

>Other than noise, is there any harm in letting this go unfixed for an
>extended period of time? Can it do damage to the block by not getting the
>heat out propoerly? Possible stupid questions but I had to ask.
>
>I have seen that most of the headers are made for manual transmission and
>that they will need some 'special routing' for auto trannies. I had the rest
>of the exhaust replaced (with standard parts, not cat-back system) a while
>back and am curious if this re-routing would require me to redo it again?
>
>At 4WD.com., the replacement manifold that they show is listed for years
>'91 - '99. Does this seem
>correct?
>
>Thanks.
>

Roy J

When you shut the engine off after a hard run, what would you
think happens to the exhaust valve about 3" away from the major leak?

bowgus wrote:
> Yeah ... I'd also like to know , first of all how "cold air", or any air for
> that matter, could possibly enter a (pressurized by the engine firing)
> exhaust manifold ... geez .. that's like saying cold air can enter via the
> tailpipe, make it's way through the exhaust sytem to the exhaust manifold
> wher it will ... and this I'd really like to understand ... damage "the
> valves". Now, in my youth I have reduced back pressure on a few autos and
> run them hard thereby burning exhaust valves ... maybe this is what you are
> thinking? Or maybe you are thinking that the O2 sensor might somehow be
> misled by the cracked manifold thereby changing the mixture? Look there is
> no argument here ... just a question as to how this works ... I am always
> eager to learn more about the jeep ...
>
>
> "Jerry Bransford" <jerrypb@mecox.net> wrote in message
> news:CUaTb.3858$1O.2264@fed1read05...
>
>>"Irish Redneck" <seeayeemm@hotmail.com> wrote in message
>>news:opr2pb0bviy2qpcc@netnews.insightbb.com...
>>
>>>On Sun, 1 Feb 2004 08:15:19 -0800, Jerry Bransford <jerrypb@mecox.net>
>>>wrote:
>>>
>>>
>>>>A cracked exhaust header should be replaced since it can damage the
>>>>valves
>>>>by letting cold air in through the crack.
>>>>
>>>
>>>please explain to me the science behind this 'fact'.
>>
>>Do your own research if you want to argue against what I said that I stand
>>behind...which on the surface sure seems like is you're itching to do.
>>
>>--
>>Jerry Bransford
>>To email, remove 'me' from my email address
>>N6TAY, PP-ASEL
>>See the Geezer Jeep at
>>http://members.***.net/jerrypb/
>>
>>
>
>
>