Exhaust Manifold: Stock vs Headers for MPG
CF Veteran
Joined: Feb 2012
Posts: 2,282
Likes: 18
From: central IN
Year: 1997
Engine: 4.0
i understand the venture effect. however, I do not understand how air and any liquid can be compared physically, I digress. nonetheless, set up a venturi tube and force your choice of content through it. poke a hole in it. it's going to leak...
I've had numerous cars with exhaust leaks before the o2. those same cars had wideband o2 sensors on them. none of the exhaust leaks altered the afr. a gaping hole pre-o2, yeah that'll cause a problem. something the size of that crack in your header...? no.
I've had numerous cars with exhaust leaks before the o2. those same cars had wideband o2 sensors on them. none of the exhaust leaks altered the afr. a gaping hole pre-o2, yeah that'll cause a problem. something the size of that crack in your header...? no.
Last edited by s346k; Sep 1, 2015 at 02:19 PM.
CF Veteran
Joined: Jan 2015
Posts: 1,508
Likes: 5
From: Oregon Coast
Year: 1999
Model: Cherokee
Engine: 4.0L I6
Exhaust Manifold: Stock vs Headers for MPG
i understand the venture effect. however, I do not understand how air and any liquid can be compared physically, I digress. nonetheless, set up a venturi tube and force your choice of content through it. poke a hole in it. it's going to leak...
I've had numerous cars with exhaust leaks before the o2. those same cars had wideband o2 sensors on them. none of the exhaust leaks altered the afr. a gaping hole pre-o2, yeah that'll cause a problem. something the size of that crack in your header...? no.
I've had numerous cars with exhaust leaks before the o2. those same cars had wideband o2 sensors on them. none of the exhaust leaks altered the afr. a gaping hole pre-o2, yeah that'll cause a problem. something the size of that crack in your header...? no.
Did you see the video?
CF Veteran
Joined: Feb 2012
Posts: 2,282
Likes: 18
From: central IN
Year: 1997
Engine: 4.0
yeah, I saw the video. I understand the scavenging qualities of a header collector, vacuum effect, etc. I'm arguing that a crack in the manifold is going to cause a rich condition as described.
edit: one thing that video is failing to acknowledge is backpressure and exhaust pulses. not only could I see carbon around the crack in the manifold, I could also feel the exhaust exiting with my finger. not to mention, my primaries on my stock header showed signs of being hot and 4 of the 6 plugs have looked a bit lean with or without the crack in the manifold.
edit: one thing that video is failing to acknowledge is backpressure and exhaust pulses. not only could I see carbon around the crack in the manifold, I could also feel the exhaust exiting with my finger. not to mention, my primaries on my stock header showed signs of being hot and 4 of the 6 plugs have looked a bit lean with or without the crack in the manifold.
Last edited by s346k; Sep 1, 2015 at 03:12 PM.
Senior Member
Joined: Mar 2012
Posts: 974
Likes: 14
From: Racine, WI
Year: 1997
Model: Cherokee
Engine: 4.0
Exhaust Manifold: Stock vs Headers for MPG
Gas is a fluid. You can't argue or disagree with this. Whether you understand it or not does not change physics.
Negative pressure at a crack does not always happen. Just because the stars aren't always aligned for it to happen doesn't change the fact that it can and does happen.
Negative pressure at a crack does not always happen. Just because the stars aren't always aligned for it to happen doesn't change the fact that it can and does happen.
CF Veteran
Joined: Jan 2015
Posts: 1,508
Likes: 5
From: Oregon Coast
Year: 1999
Model: Cherokee
Engine: 4.0L I6
Exhaust Manifold: Stock vs Headers for MPG
Gas is a fluid. You can't argue or disagree with this. Whether you understand it or not does not change physics.
Negative pressure at a crack does not always happen. Just because the stars aren't always aligned for it to happen doesn't change the fact that it can and does happen.
Negative pressure at a crack does not always happen. Just because the stars aren't always aligned for it to happen doesn't change the fact that it can and does happen.
CF Veteran
Joined: Jan 2015
Posts: 1,508
Likes: 5
From: Oregon Coast
Year: 1999
Model: Cherokee
Engine: 4.0L I6
Member
Joined: Feb 2009
Posts: 219
Likes: 1
From: Southwestern Indiana
Year: 1996
Model: Cherokee
Engine: 4.0
my stock manifold was cracked. I don't buy the lean condition caused by a cracked manifold. how does air get sucked into a highly pressurized system through an opening thinner than a sheet of paper? I saw no different mpg after repairing the manifold. I can only assume a more efficient header will afford a mileage increase assuming you aren't frequently employing the newfound efficiency with the skinny pedal.
Honestly, there are many possible factors controlling why yours may not be having an issue including where the crack is in relation to the sensors, however the issue of a cracked manifold sucking in air and throwing off the sensor really isn't debatable. Its a common occurrence and easily repeatable.
Junior Member
Joined: Apr 2011
Posts: 93
Likes: 1
From: Music City
Year: 1994.5
Model: Cherokee
Engine: Inline 6 4.0 HO
my stock manifold was cracked. I don't buy the lean condition caused by a cracked manifold. how does air get sucked into a highly pressurized system through an opening thinner than a sheet of paper? I saw no different mpg after repairing the manifold. I can only assume a more efficient header will afford a mileage increase assuming you aren't frequently employing the newfound efficiency with the skinny pedal.
You do realize that metal expands when heated , right? Heh, this is a topic that's been covered & validated for ,like,ever ? A cracked manifold does suck air in as it expands ....it can expell the same type of air that appears to flow plentifully between your ears ,as well....
Srry to butt-in ,but as I read this reply I just..... sheez.....
CF Veteran
Joined: Feb 2012
Posts: 2,282
Likes: 18
From: central IN
Year: 1997
Engine: 4.0
Wow.
You do realize that metal expands when heated , right? Heh, this is a topic that's been covered & validated for ,like,ever ? A cracked manifold does suck air in as it expands ....it can expell the same type of air that appears to flow plentifully between your ears ,as well....
Srry to butt-in ,but as I read this reply I just..... sheez.....
You do realize that metal expands when heated , right? Heh, this is a topic that's been covered & validated for ,like,ever ? A cracked manifold does suck air in as it expands ....it can expell the same type of air that appears to flow plentifully between your ears ,as well....
Srry to butt-in ,but as I read this reply I just..... sheez.....
CF Veteran
Joined: Sep 2009
Posts: 1,142
Likes: 2
From: Grand Prairie, Texas
Year: 1998
Model: Cherokee
Engine: 4.0 HO I6
