Question about the factory crush

[dukie564]

Ummmm... no.

It IS there for clearance and it WON'T have an appreciable affect on the torque curve, gas mileage, or "motor feel"

Actually it really is there for back pressure reasons. It's not in a spot on the downpipe that the driveshaft would ever come into contact with. It is strategically placed on the outside bend to disrupt the laminar flow of the exhaust. Another hint from the 93/2000 FSM is the backpressure testing procedure: it is done by removing the first Oxygen sensor....specifically, "1 3/4 - 2 psi while running is correct"....and is necessary for proper motor functioning. [/QUOTE]

 

[hubs97xj]

It's not in a spot on the downpipe that the driveshaft would ever come into contact with.

I respectfully disagree. Stock height, replacement pipe had the same dimensions and routing. This was the result of pulling into a driveway.

 

[Milford Cubicle II]

That crush in your exhaust pipe will not create a "better" torque curve. And you don't need any back pressure for a "properly functioning motor." And jeep certainly didn't "tune" their exhaust to that level.

That testing procedure is probably to test for a damaged cat or some other obstruction in the exhaust.

 

[kastein]

I respectfully disagree. Stock height, replacement pipe had the same dimensions and routing. This was the result of pulling into a driveway.

this is exactly what I was going to say. Thank you.

93/2000 FSM? Which one? One of those has the sensor well below where that crushed spot is, the other has one above and below each pre-cat and... has no crushed spot. The one with the sensor well below the crushed spot (93 FSM) means that when you measure the pressure, you are not measuring the backpressure because of the crushed spot, you are measuring the backpressure because of the cat/muffler.

 

[rocknxj]

Good thread and great debate. I had my factory dent cut off and new downpipe built last summer, but I wish I never messed with it since the muff shop dicked it so badly. I noticed a very loud intake whistle immediately after downpipe and muffler installation. I suspected the change in backpressure aggravated the intake leak. Long story, but I had no noticeable leak after APN header installation, but I did after muffler/downpipe install.

I have always wanted to know the real reason for the dent, be it for clearance or back pressure. I look forward to the definitive answer (with proper source info) for this question. Meanwhile, I still plan to have an improved downpipe rebuilt.

 

[mizzutgr]

I just looked again at my crack at the collecter- it is bigger now- probably happened on install of the new pipe. The O2 senser is factory, but the muffler guys said he had no problems removing it and it was still good. How does a mechanicly challenged person test to see if it is still good AND does anybody live near columbia ,mo that could do a apn header install on the cheap ?

 

[cruiser54]

Right after the exhaust pipe attaches to the header, the factory put a "crush" in the round pipe to clear the front driveshaft when the suspension compresses. It probably reduces the volume of the pipe by 25%.

Go look at your Jeep when you get a chance.

 

[Milford Cubicle II]

I just looked again at my crack at the collecter- it is bigger now- probably happened on install of the new pipe. The O2 senser is factory, but the muffler guys said he had no problems removing it and it was still good. How does a mechanicly challenged person test to see if it is still good AND does anybody live near columbia ,mo that could do a apn header install on the cheap ?

I've had to replace my header gasket about... 11 times. So I'm kind of a pro at doing header installs now.

And I'm definitely cheap

Still got my number?

 

[DieselSJ]

That crush in your exhaust pipe will not create a "better" torque curve. And you don't need any back pressure for a "properly functioning motor." And jeep certainly didn't "tune" their exhaust to that level.

That testing procedure is probably to test for a damaged cat or some other obstruction in the exhaust.

Agreed. And Milford and I don't agree on everything. ;-)

 

[old_man]

It is NOT for clearance.

Funny thing, I replaced my exhaust without the crush and after some hard wheeling, it magically appeared again except this time it was nice and shiny.

 

[mizzutgr]

Milford- found your #, will give you a shout sometime.

 

[Shorty]

Funny thing, I replaced my exhaust without the crush and after some hard wheeling, it magically appeared again except this time it was nice and shiny.

that just goes to prove how badly the engine "wants" the restriction.

On a side note, didn't the crush/dent/defect/intentional restriction go away with the introduction of the LP D30?

 

[old_man]

Good question. I only run the good XJ's, RENIX rules.

 

[casm]

On a side note, didn't the crush/dent/defect/intentional restriction go away with the introduction of the LP D30?

Nope - my 2000 has both.

 

[Shorty]

huh, I'll have to find that old thread and S.P.O.B.I. them!!!!!

 

[Milford Cubicle II]

Agreed.

:scared:





:roflmao:

 

[DieselSJ]

:scared:





:roflmao:

 

[Talyn]

Nope - my 2000 has both.

My 2000 doesn't have the crush. It had the LP D30 and the Cali emissions package.

 

[casm]

My 2000 doesn't have the crush. It had the LP D30 and the Cali emissions package.

Interesting. What was the date of manufacture on yours? Mine's 01/2000, and as far as I know I'm still running the factory exhaust with the exception of the catalytic converter.