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Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go hereXJ (84-01)
All OEM related XJ specific tech. Examples, no start, general maintenance or anything that's stock.
Cruiser54 knows. Look into how he came to know what he knows and the source of his information.
What he says on the matter is parallel to and consistent with my experience and observation in separate but similar circumstance. It's to warm the O2 sensor quicker.
I guess one other glaring question that I have is if it was done to every vehicle, why didn't they design a pipe with a restriction or bend or crimp. Why is every single one literally bashed on with a hammer. Mine is smashed in on multiple sides severely. There doesn't seem to be much Rhyme or Reason to it.
There are many "upgrades" that seems to be really common among jeepers... that down the road we find negatively impact other areas of performance in an unanticipated way. The people that knew this vehicle better than anyone on the planet, designed it that way. I fear changing things sometimes has unintended consequences in other areas, even if you see an increase in performance you were looking for.
a lot of vehicles made around this era had exhausts considerably restricted to their predecessors due only to emission laws
some "stock" things are a compromise, (or just hopeless, like the pre-update headlight harness)
a bigger exhaust will cause more noise and fuel consumption than desirable for a stock vehicle
I would only bother to make the change when my exhaust needed replacement, mine came to me as they were
If you browse the Internet, you will see aftermarket exhaust is one of the few things proven on dyno to give more power on an XJ
Or.....somebody at the plant that produced them stated when asked why he was putting a dent in the pipe "I dunno, they said make sure all the pipes matched and one came through with the dent"
You ever see those dents in airplane, harley or race car exhausts ?
Me neither.
I don't know if I'd use HD as an example of engine performance.
Originally Posted by 4x4jeepmanthing
I replaced my banks header today. In doing so I got to looking at the downpipe and its dent. Now I know a billion folks have asked if this is restrictive and that it was a factory added bend for emissions purposes.
What Ide like to know the truth of is, does replacing this dent with clean tube aide in a reduction of torque and/or power loss via lack of backpressure, or would it actually gain some power/torque.
I know with the new header I'm getting a little further into the seat which is cool, now I'm curious if there's any reason not remove the dent?
Originally Posted by Heaving Earth
I haven't fixed mine yet. I also thought about going to 2.5 and decided against it on account of hearing somewhere (probably this forum) with less back pressure form 2.5 the gases move too quickly for the O2 sensors to collect accurate data and can cause some issues. I instead, decided to go with a header and magnaflow high flow cat and muffler for a little better flow without accidental overkill. I have the header and cat in but need to add the muffler and all new pipes when I can afford it.
EDIT: I know a lot of people here have gone to 2.5 and I don't think they had many issues. Maybe someone with 2.5 can educate us.
I hope this helps.
Just to clear up a common misconception, "backpressure" is not really a thing. What's important is exhaust velocity and its impact on scavenging in the cylinder. Going up to 2.5" from 2.25" would actually slow down the exhaust flow.
Seeing as how my driveshaft beats against the pipe on acasion and the dent appears be there to help beat on it alittle less.
Im not actually sure a round 2.5" pipe will fit there. Itl for sure have hug the side of the block and oil pan as tight as possible. I really like doing exhaust work but have not convinced myself doing a 2.5" down pipe will help so ive decided to leave it till it needs fixing.
I don't know if I'd use HD as an example of engine performance.
Just to clear up a common misconception, "backpressure" is not really a thing. What's important is exhaust velocity and its impact on scavenging in the cylinder. Going up to 2.5" from 2.25" would actually slow down the exhaust flow.
does this apply to an exhaust that is not dual or x pipe?
the header exits at 3" or so into the dent, wouldn't removing the dent allow higher velocity or less restriction? If the engine is a pump don't you want air in/out with as little resistance as possible?
Last edited by 4x4jeepmanthing; Jan 12, 2021 at 12:08 AM.
