Why is there a dent in the exhaust pipe just below the exhaust manifold and above the up stream 02 sensor? I am assuming this is to maintain "optimal back pressure" but has any one removed this, would are there be any benefits to removing it?

mine has a dent in the same place not as bad tho i thought it was something i did?

Haha, I thought I got a rock up in there!!

It's for clearance of the front drive-shaft. Apparently it was a tight fit on a stock rig in certain flexing positions. I'd be willing to say in a lifted rig it would never be an issue, still I believe it's necessary for back pressure.

Correct. As far as backpressure goes, the optimax backpressure for any internal-combustion engine is none, per Taylor and Morrison.

Taylor - The Internal Combustion Engine in Theory and Practice, Charles Fayette Taylor, MIT Press.

Morrison - Scientific Design of Exhaust & Intake Systems, Philip H. Smith & John C. Morrison (easier to cite as Morrison instead of Smith - "Smith" is too common as a name.)

These works are considered definitive on the subject. Anyone who tells you that an engine "requires backpressure" to operate efficiently is talking through their hat. Backpressure inhibits scavenging, which inhibits cylinder emptying and filling, which robs you of power.

Full stop.

(Sorry, but I get very tired of hearing about how an engine "needs backpressure" to run - I've read too much literature staying otherwise, and presenting data as proof.

I've got a reading list for detailed IC engine theory up on my site, but I probably do need to add a few things and update others (for instance, The Bosch Automotive Handbook is now on its eighth edition, and there are plenty of changes between it and the sixth edition - which is the other one I have.)

That dent is stupid. When I put the banks manifold on I had a new pipe bent up out of 2.5 instead of 2.25 and put a Jeg's universal 2.5 cat on to a 3" muffler and pipe. Much less "back pressure" and runs just fine.

I asked this question of my friend at Jeep Engineering a few years ago. It is NOT there to clear the front driveshaft, but was put there to appear that way. It's purpose is to keep the exhaust gasses hotter when they enter the converter.

Ah. It's nice to be green.

im so angry i can't find this for free any where, cause i really wanna read them now, grrrrrrrr, maybe i can find some papers written on those books, got any linkable material?


oh and what was that thing about misinformation? i have heard back pressure my whole life, and its a lie?... going chop right before the cat now! obv not serious so dont flame me

I don't think its for driveshaft clearance, mine was making contact during a wheeling trip this past weekend. and I've got around 5 inches of lift

with a trackbar at more of an angle and axle centered perfectly at ride height the axle will swing over more to the passenger side on suspension compression.

Moved to OEM Tech since we are discussing OEM equip.

Just so people ask ? about it.

Mine too. But my contact was lower. Right at the loxer 90bend?

I always thought it was put there in order to, somehow, pass emission tests?