Catalytic converter flow rate

Could someone please let me know the flow rate (in CFM if at all possible) of the stock catalytic converter as attached to a 2000 XJ with the 4.0-litre? I'm looking at having to replace mine and would prefer to go aftermarket but not overspec it. Cheers!

Going with a converter that flows more shouldn't be a problem - it just removes what would normally be a flow restriction (to a certain extent.)

I usually use "universal fit" catalytic converters sizes for BBChevvy motors, which don't cause any trouble for me, opens the exhaust up a bit, and makes the El Cheapo Walker Turbo II mufflers I use sound good. A decent welder can stick some pipe to the bolt flange for you in a few minutes - and I do suggest you keep that bolt joint, rather than having the whole system welded.

I usually have to work "on the cheap," and the BBChevvy converters are actually some of the cheapest out there. The Walker mufflers go for about $18 - just find the right pipe size and location, and you're there.

I'm not big on fancy, and (according to my MkIII Butt Dyno) I seem to get a little pickup from the aftermarket parts just by picking something a little more open.

No, I don't have any trouble at all passing smog...

The only thing you'll really want to worry about is making sure you can remount the downstream HEGO sensor - so you might have to have a bung welded on, or preserve the original pipe while you're replacing parts. Up to you...

5-90

5-90 said:

Going with a converter that flows more shouldn't be a problem - it just removes what would normally be a flow restriction (to a certain extent.)

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Understood. My main concern was opening it up too much - since I'm planning on keeping the stock muffler for now (I have too much in pennies and JB-Weld invested into it at this stage to let it go ), spending $400 on a cat that would just be restricted by the muffler anyway seems pointless. I also didn't want to end up with a situation whereby I'm eliminating backpressure.

I usually use "universal fit" catalytic converters sizes for BBChevvy motors, which don't cause any trouble for me, opens the exhaust up a bit, and makes the El Cheapo Walker Turbo II mufflers I use sound good.

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OK - so something suitable for, say, a 5.7-litre engine would be OK? Is there a specific application I should quote when buying it? Sorry for the dumb questions, but all my past dead cat experiences have been one-to-one replacements.

A decent welder can stick some pipe to the bolt flange for you in a few minutes - and I do suggest you keep that bolt joint, rather than having the whole system welded.

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Yup, this is the plan - people forget that exhausts like to be able to flex a little.

I'm not big on fancy, and (according to my MkIII Butt Dyno) I seem to get a little pickup from the aftermarket parts just by picking something a little more open.

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Same here. Actually, even a straight drop-in replacement would be an improvement, since mine seems to be shot. I figure that if I'm going to have to replace it anyway, may as well go to something a bit less restrictive while the guy's at it.

The only thing you'll really want to worry about is making sure you can remount the downstream HEGO sensor - so you might have to have a bung welded on, or preserve the original pipe while you're replacing parts. Up to you...

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Yeah, that would be nice, seeing as how I just replaced both of them not two months ago Fortunately, I've got a muffler guy who's a whiz at the cut & weld routine in tight spaces.

Yah - if you tell them the inlet and outlet sizes, and that you want a cat for a 305 or bigger, you should be fine. The one I got last time (free!) happened to be designed to go behind a 454, so I don't see a lot of trouble anytime soon...

I usually use PFP universal fits (Products for Performance, I think - just ask for PFP) since they can usually be had for less than $100 (I think the last one I had to buy ran me about $75 or so.) You can save BUCK$ if you're willing to adapt things...

5-90

5-90 said:

Yah - if you tell them the inlet and outlet sizes, and that you want a cat for a 305 or bigger, you should be fine. The one I got last time (free!) happened to be designed to go behind a 454, so I don't see a lot of trouble anytime soon...

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Mkay, good to know. Right now I'm at the point where this needs to be done TODAY (it's fairly plugged and causing all the usual dead cat symptoms) and am trying to locate a cat so I can get it over to my guy. Since I'm heading out to Las Vegas at the end of next week, it's fairly crucial this gets taken care of before doing a 600-mile round trip because 14mpg there and back would really, really blow.

Out of curiosity, do you happen to know if there's a difference between California and other-state XJs in the 2000 model year as relates to the cat? I keep turning up the 'not California-compliant' catalytic converters through Kragen, AutoZone, etc. but have no idea what the difference is. FWIW, mine originally came in here from Michigan by way of Oklahoma, so I'm guessing it's probably not a CA model to begin with. There's nothing indicating one way or the other under the hood, at least not that I've found yet...

Check the emissions tag - it will say it either conforms to "California Emissions Standards" or "Federal Emissions Standards" - if you have the 49-states, you can do pretty much whatever you want.

Having said that, I've got a Federal BBChevvy catalytic converter on a California 4.0XJ, and wouldn't you know I just blow right through the smog check? Amazing...

Be prepared to point out the "Federal" standards notice if you have it - it can get you a little wiggle room.

Most manufacturers are required to point up the fact that CA doesn't like to allow changes - basically, what they're saying is "We haven't gone to the trouble to get a CARB EO # because we think it's a pain in the a$$" (and it is.) Unless it's a a visibly obvious change, you're likely to get away with it in CA.

If your vehicle carries a 49-state registration, don't even fret about CA - you don't have to deal with this onerous ()*#)&@#*()$& anyhow. Most states I've heard of doing smog checks don't even do the visual check - which is as it should be.

5-90

5-90 said:

Check the emissions tag - it will say it either conforms to "California Emissions Standards" or "Federal Emissions Standards" - if you have the 49-states, you can do pretty much whatever you want.

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Sounds good. FWIW, I'm going through a new kind of hell: the best quote I've got so far to do this job is $300, which includes the cat. Everyone's pulling this 'OBD-II cats are more complex' routine on me, and I'm not buying it so far - I mean, the only real difference should be that there's a bung in the rear of the cat for a second oxygen sensor, right?

Having said that, I've got a Federal BBChevvy catalytic converter on a California 4.0XJ, and wouldn't you know I just blow right through the smog check? Amazing...

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Go figure

If your vehicle carries a 49-state registration, don't even fret about CA - you don't have to deal with this onerous ()*#)&@#*()$& anyhow. Most states I've heard of doing smog checks don't even do the visual check - which is as it should be.

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Unfortunately, it doesn't - sold new in Michigan, ended up being registered here by way of Oklahoma last year sometime. I hate the DMV with a passion; having once been the recipient of a 90-day export-or-destroy order on a vehicle I bought because they couldn't find it in the computer (despite my having several years' worth of back registrations for it), they can eat a turd in hell for all I care.

I'd have to check (damn, but I hate smog regs...) but I seem to recall the fact that if it was built as a 40-state vehicle, it STAYS 49-states. Have you check with CARB yet? They're online... Might even be a FAQ on it.

FAQ-it!

5-90