Exhaust

[stevekop]

Have to replace my exhaust on 89 Comanche.  Will be replacing all the pipes should I also replace the cat. converter.  Far as I can tell there is no problem with it.

[HOrnbrod]

Unless your state requires emission testing on 25+ year old vehicles, bypass it. They tend to clog up with age.........

[gogmorgo]

I think some clarity is needed as to whether "should I replace it" means "Should I reuse my current catalytic converter with the next pipes" or "should I bother installing a catalytic converter when I replace the exhaust system".

The answer to "should I replace it" is going to be yes. Unless something untoward has happened (wouldn't surprise me) it is illegal to tamper with emissions equipment under US federal law. It was put there for a reason, and if you don't know how long it's been there and your exhaust system is in poor enough condition to warrant replacing the entire thing, it's probably not doing much any more to reduce emissions.

That said, the chances of being prosecuted for tampering with your vehicle's emissions system are incredibly slim, especially under your current administration, and especially if there's no requirement for emissions testing. Similar laws are in effect here in Canada, and despite the fact that our current administration claims to care, there's also very little chance I'll be prosecuted for two of my three vehicles not having the cats they should have. However that's more due to the fact that I'd rather spend the money somewhere else because both the vehicles blow enough soot out the exhaust any cat would be rendered useless in short order than anything else. You won't notice any significant performace improvement in just removing the cat from the system, but your children's children will have a much healthier life as a result.

[onlyinajeep726]

I think some clarity is needed as to whether "should I replace it" means "Should I reuse my current catalytic converter with the next pipes" or "should I bother installing a catalytic converter when I replace the exhaust system".

The answer to "should I replace it" is going to be yes. Unless something untoward has happened (wouldn't surprise me) it is illegal to tamper with emissions equipment under US federal law. It was put there for a reason, and if you don't know how long it's been there and your exhaust system is in poor enough condition to warrant replacing the entire thing, it's probably not doing much any more to reduce emissions.

That said, the chances of being prosecuted for tampering with your vehicle's emissions system are incredibly slim, especially under your current administration, and especially if there's no requirement for emissions testing. Similar laws are in effect here in Canada, and despite the fact that our current administration claims to care, there's also very little chance I'll be prosecuted for two of my three vehicles not having the cats they should have. However that's more due to the fact that I'd rather spend the money somewhere else because both the vehicles blow enough soot out the exhaust any cat would be rendered useless in short order than anything else. You won't notice any significant performace improvement in just removing the cat from the system, but your children's children will have a much healthier life as a result.

 

^^ This.

[desbennett004]

Just knock the guts out of it and weld it back in empty.

 

Sent from my SM-N900W8 using Tapatalk

[HOrnbrod]

I think some clarity is needed as to whether "should I replace it" means "Should I reuse my current catalytic converter with the next pipes" or "should I bother installing a catalytic converter when I replace the exhaust system".

The answer to "should I replace it" is going to be yes. Unless something untoward has happened (wouldn't surprise me) it is illegal to tamper with emissions equipment under US federal law. It was put there for a reason, and if you don't know how long it's been there and your exhaust system is in poor enough condition to warrant replacing the entire thing, it's probably not doing much any more to reduce emissions.

That said, the chances of being prosecuted for tampering with your vehicle's emissions system are incredibly slim, especially under your current administration, and especially if there's no requirement for emissions testing. Similar laws are in effect here in Canada, and despite the fact that our current administration claims to care, there's also very little chance I'll be prosecuted for two of my three vehicles not having the cats they should have. However that's more due to the fact that I'd rather spend the money somewhere else because both the vehicles blow enough soot out the exhaust any cat would be rendered useless in short order than anything else. You won't notice any significant performace improvement in just removing the cat from the system, but your children's children will have a much healthier life as a result.

 

:yes:   In other words, "Do as I say and not as I do blah blah..............."     :smart:

[johnj92131]

Do as I did, even if I am not required to get 2 of my vehicles smog checked in Southern California. 

 

First, my 1996 Passat TDI came with a catalytic converter.  I left it in place, even as my 96 is exempt from smog checks when I upgraded the turbocharger and down pipe.

 

Second, my 1986 diesel Comanche now getting a VW TDI engine.  Since the old Renalult 2.1 diesel never came with a catalytic converter, I have opted to remove the catalytic converter from the 98 VW TDI engine that is going in to the 86 Comanche.

 

So bottom line, if your truck came with an OEM converter, I say keep it in place. No real point to spewing out more crap than you currently do.  Your truck will not run any better without the convertor.

 

In the end, it is your choice.

[ScottJeep]

It really depends on your area and what you intend to do long term and short term. 

 

Here in Atlanta-Cali there are emissions based on age.  

But even after the vehicle is exempt most muffler shops around me will not even touch a vehicle that has had the catalytic converter removed. Which can make getting a new setup installed on a vehicle after it has been "non-emissions required" altered a PITA.  They are too paranoid that they are being setup for fines/being shut-down. 

 

It can get even more fun if someone in a non-emissions county alters prior to the official time that the rest of the area is required to deal with.  

Say...removing catalytic converts on a 2001 XJ to make it "sound n" run better".  It becomes very difficult based on the above situation to get it straighten out 

AND

Here it is also illegal to sell a vehicle in/into an emissions requiring county knowing it will not pass (visual or sniffer or both doesn't matter ).  

 

The true enthusiast has to pay attention and know how the rules work and how to get stuff done if not doing it themselves.

 

If the thought of selling is even slightly possible ( my latest "project" is vehicle #47 ) and it originally came with a catalytic converter it get another. 

Normally a MagnaFlow unit. Cheap, performance designed and Summit carries them so it is usually, order one day, arrives the next by lunch. 

[gogmorgo]

:yes: In other words, "Do as I say and not as I do blah blah..............." :smart:

Pretty much, haha.

 

In my case, the Niva didn't have one and the MJ's did more to reduce tailpipe emissions by redirecting them away from the tailpipe, so by not putting one in when I very cheaply redid them both I wasn't really changing anything. Plus like I said the amount of oil the MJ burns the cat would plug full of soot before it had the chance to do anything.

I haven't looked into it yet, but if I'm required to re-tag my MJ with the upcoming move (pretty sure I will be) and it needs to have a cat to pass an inspection, I will happily install a functioning cat. I might even be temped to blow thickening apart to fix the oil consumption problem to make it worthwhile. But I'm pretty lazy.

[NC Tom]

Your truck will not run any better without the convertor.

 

Disagree. Catalytic converters are, by nature, a restrictive system. Remove it and you'll gain torque, hp and be more efficient. However, know your local ordinances. Large or small, the gains ain't worth the potential fines. :no:

[gogmorgo]

Have you ever looked inside a cat? It's just a bunch of hollow tubes. Tiny amount of turbulence transitioning between the large tube of the exhaust pipes and the many smaller tubes and then back again but it wouldn't surprise me if it had less of an effect than a glass pack would. Punching it out to make it only look like a cat on the outside probably will increase the effect on performance due to the large empty chamber and the many horribly distorted tubes around the outside increasing turbulence.

With a properly functioning system you're looking at most at a 2% difference in performance, which on something with under 200 hp is not even going to be noticeable on a racetrack let alone on a street-driven vehicle. The only noticeable difference maybe is going to be in sound.

[HOrnbrod]

Have you ever looked inside a cat? It's just a bunch of hollow tubes. Tiny amount of turbulence transitioning between the large tube of the exhaust pipes and the many smaller tubes and then back again but it wouldn't surprise me if it had less of an effect than a glass pack would. Punching it out to make it only look like a cat on the outside probably will increase the effect on performance due to the large empty chamber and the many horribly distorted tubes around the outside increasing turbulence.

With a properly functioning system you're looking at most at a 2% difference in performance, which on something with under 200 hp is not even going to be noticeable on a racetrack let alone on a street-driven vehicle. The only noticeable difference maybe is going to be in sound.

 

That's bull. Catalytic converters are restrictive. They do make a difference on the dyno. I've seen it. My first dyno run at Hesco back in 05 to establish a baseline with the fresh new stroker was with Leach headers and the stock exhaust w. the stock cat. Lee Hurley said the cat is strangling it. While there they welded in a cheap Magna Flow high flow cat and the torque and HP peaks went up ~9HP on the second run.

 

Came back a month later with a new split dual 2.5" exhaust all the way back with NO cat, and the peaks went up another 12HP. So yeah, cats are restrictive. Gotta balance the suck and blow. And it's come a long way since then.

 

But I agree somewhat with you; probably on a N/A 4.0, there won't be much difference w. or w/o a cat  with the stock intake system. But until it's proven on the dyno,  :dunno:

[1989 comanche mj]

The complete exhaust is easy to do on these yourself.  I fit them, clamp them then drop them down and fully weld and reinstall.  Don't reuse the converter, if its full still sell it ($30) and buy an aftermarket one.  The factory one will fail and clog the muffler eventually.

[Jeep Driver]

New engine, new NOS TBI, new 55lbs injector, all sensors are OEM except ECM temp sensor for which I'm currently looking for, AMC or Mopar. Engine runs perfectly with one exception, it runs rich. 

 

I contacted the company that I got the TBI from and explained the situation, I got a quick lesson in tuning injector to the engine. 

 

My fuel pressure gauge came today, it will be permanently attached to the TBI, no more guessing or wondering. 

 

My MJ is slated for a new dual exhaust next month, I'm waiting to replace my springs (military wrap group buy) before the exhaust so I don't have to work around the cans and tips. 

 

No Cat now, no Cat in the future. 

 

I'm going to have the speed shop that's doing the exhaust weld a second bung in for a wide band AFR gauge in the future. 

For now, knowing the fuel pressure will at least give the injector shop some information to work with. 

 

 

 

 

 

Why am I explaining my current situation? 

 

I'll tell what a Cat would have done, masked a rich condition.

 

 

 

 

 

I see all kinds of FP numbers and guys swapping this injector and that. The only exception are guys running superchargers, no one else making an effort to tune their engines. 

 

 

 

Cats will not save the world, nor my great great great grandkids. 

 

 

 

[gogmorgo]

That's bull. Catalytic converters are restrictive. They do make a difference on the dyno. I've seen it. My first dyno run at Hesco back in 05 to establish a baseline with the fresh new stroker was with Leach headers and the stock exhaust w. the stock cat. Lee Hurley said the cat is strangling it. While there they welded in a cheap Magna Flow high flow cat and the torque and HP peaks went up ~9HP on the second run.

 

Came back a month later with a new split dual 2.5" exhaust all the way back with NO cat, and the peaks went up another 12HP. So yeah, cats are restrictive. Gotta balance the suck and blow. And it's come a long way since then.

 

But I agree somewhat with you; probably on a N/A 4.0, there won't be much difference w. or w/o a cat with the stock intake system.

I won't disagree with your findings but I'm not convinced they're evidence of much. We're also talking about an engine with 13% higher displacement, pushing a lot more air than your stock cat was intended to handle. The 12hp gain after the no-cat system will have more to do with the increased pipe diameter than the lack of cat, as well.

You can't properly compare one variable when you're changing a bunch of others.

[HOrnbrod]

You made the statement that a stock cat is not restrictive. It most definitely is. It has to be to effectively do it's job. And the older it gets, the more restrictive it becomes. The 9HP gain on the first dyno run was with another cat, a somewhat less restrictive one at that, which translated into a 9HP gain. So maybe that would be 4.5HP or whatever gain on an N/A 4.0, who knows until it's dynoed? Lots of variables as you say. But w/o proof you are spouting pure conjecture. 

 

Your statement that the cat "wouldn't surprise me if it had less of an effect than a glass pack would" was ludicrous. The below is my cat now. It's there only to cut down the resonant exhaust drone noise inherent in all 6-cylinder engines. It had zero restrictive results. Also dyno proven before and after. Go on over to the strokers forum to see the results. Maybe you will be surprised. I'm done with this now..........

 

[DirtyComanche]

I don't even have a 'bama cat on my XJ.  Just a tiny little "Pypes" muffler tucked up by the rear axle.  It's 2.5" stainless all the way too.

 

Performance wise, who knows, 37s with 4.10 gears and about 1000lbs of extra axle and suspension parts means I'm clawing for every HP I can get.