I thought i shoved a big stick/branch up there when trailing. Haha. Shows how much i know about exhaust systems.

 

Sway bars disconnected and Didn't bump stop with the lift did ya?.........That'll end well.

 

Good luck - MIT Press books are universally spendy. Bentley Publishing should have Morrison.

And, that's nowhere near all of the literature on the subject that could be considered "definitive," my selections run from about 1930 to ten years ago.

Misinformation? Yeah - I've been hearing the same misinformation all my life.

I do know about the idea of going with a smaller exhaust passage to retain heat and improve catalyst light-off times (that's why the exhaust ports on the 0331 head as so small,) but that could also be resolved by component location, rather than just restricting exhaust (which hampers things.)

Kinda like how they went with EGR to reduce NOx emissions - let's crap up the intake with carbon and throw water on the fire, when ther are better ways to solve the problem (water/MeOH injection was done in WWII on piston-driven aircraft to allow high-altitude performance improvement - the technology has since been shown to be beneficial to reducing NOx emissions, reducing ONR on high-compression engines, and to clean the combustion chamber without crapping up the intake with carbon. In this case, the 'water on the fire' analogy doesn't apply - because you're using less water than you are using exhaust gas. The water soaks into carbon deposits and blasts them loose when it flashed into steam, the addition of MeOH reduces the boiling point of the water (which helps with the flashing,) using water and MeOH doesn't introduce carbon into the intake stream, it can be done with a sprayer plate under the throttle body, and the system overall is somewhat more reliable than the EGR setup (and the parts would be less expensive.)

Using water/MeOH would also allow for elimination of the catalytic converter and still maintaining tailppe emissions levels at or below levels with all of the emissions equipment.

But, Federal regs get in the way (doesn't matter how beneficial such removal would be when it's all done, you're still not allowed to remove an OEM emissions control device.)

Considering the advances catalytic converter matrix design, you can actually get a catalytic converter that flows marginally better than a straight section of pipe - cf: Random Technologies.

 

Not to thread hijack, but how long should one expect a Hi-Flow cat (Magnaflow) to last? I replaced my Cat and both O2 sensors about 5 years ago (55,000 miles) and every once in a while now I throw a CEL with a code for a bad cat.

 

Good question. I'd like to know too!

 

I will agree with you on this. I had a 66 Malibu (350 small block) that I would run with open headers on the weekend just cuz it mad it sound f*****g mean. I did lose tremendous amounts of power due to not having a big cam in it but it ran fine with no issues.

 

So I'm hoping you (or anyone else for that matter) can answer this question. If I replace that pipe with one that isn't dented and exhaust gasses move more freely, do you think I'll have issues with smog testing here in Commufornia?

 

Great topic! I have always wondered this myself! Thanks to a great community, now I know!

V/r,
-awsgrayrd.

 

Cats can last years - but it's a variable.

Bear in mind that a 'bad cat' CEL simply means that you've got a sensor reading out of range - it can just as easily be a bad sensor as a bad cat.

The "upstream" HEGO (closer to the engine) is the feedback loop for fuel trim, the "downstream" HEGO (farther from the engine) is there to monitor catalyst efficiency.

But, a HEGO CEL/MIL and DTC can mean the sensor itself has failed just as much as it could mean that whatever its monitoring has gone awry.

Spec life on the HEGO runs 60-80kmiles - and has as long as they've been around. But, it was easier to "push" that life with pre-OBD and OBD-I rigs, OBD-II rigs are a good deal picker about their sensor signals.

 

The tents are there because of the black dome in the roof....

 

Being from Cali myself, you will have no issues with replacing it. I upgraded my old 1980 Chevy 4x4 dual exhaust from 2" to 3" on both sides and it didn't effect the smog testing at all. So long as you don't remove the cat it shouldn't be an issue. Disclaimer "removing the cat is illegal and nobody wants to be fined for that lol"

As far as the XJ goes, I'm replacing my whole exhaust system here in a couple weeks with 2.5" pipe from the header back. New magnaflow muffler and new CA emissions approved cat. From other exhaust experts I've talked to, I will gain some power from opening up the exhaust not to mention a nice sounding system. But this is your rig so you do what's best for you. I'm no expert I'm only speaking from my experiences with smog tests n what have you.

 

LOL ...ing
OR, and WA pretty much follow CA's lead esp with laws, regulations, fees and vehicle requirements.

Nice to hear. I been wanting to replace my pipe also. It looks like it was scraped on something (PO)

Oh, BTW, as far as I'm concerned - looking under my car without a warrant is an ILLEGAL SEARCH!

 

2.5" ID is about as far as you should go - go much farther, and you'll actually lose performance due to exhaust turbulence caused by uneven cooling of the exhaust gas pulses (this is why the ricebois with the 1500c/c Honda Civic engines and the 4" exhaust - with no turbocharger - run like rotten *** when they're driving around. With a turbocharger, the "optimax pipe size" goes right out the window - but without, there are tuning rules and formulae that apply.)

 

I found that dent on my exhaust the other day and said to myself...

"WTF previous owner"

lol

 

Here's my .02 FWIW. Jon, correct me if I'm wrong.

I'm thinking the dent is there to help the converter heat up faster from a cold start. Therefore, by the time you had your emissions test, the cat would be plenty warmed up already.