'76 CARB Catalytic Converter options?

I am rescuing a '76 XJ6C whose original catalytic convertor(s) was removed by P.O. and a standard non-cat exhaust system installed. (In California, to pass Smog they must be original catalysts, but recycling yards are required to dispose of old cats; or new cats approved the Ca Air Resources Board.) We know it originally had a catalytic convertor system because of the Catalyst/EGR warning light above ignition switch.
Fortunately, Magnaflow make CARB compliant catalytic convertors that can be fit to a 1976 XJ6. For the front location, they offer two choices:
#337304 2" Inlet, 2" Outlet 4" Wide x 8" Long
#337305 2.25" Inlet, 2.25" Outlet 4" Wide x 8" Long
Why two sizes to pick from? Did some XJ6 have two front cats, a 2" inlet size in each downpipe, while others had a 2-into-1 downpipe that connected into a single 2.25" front cat?

For the rear cat location, they offer only one choice:
#338037 Two 2" ‘inlets’ and One 2.5" ‘outlet’ (may also have an O2 sensor mounting hole?)
Do all catalyzed XJ6’s have a rear cat, or only the later ones with fuel injection? (The inlets/outlets must be reversed in Magnaflow description - the exhaust actually comes in the single 2.5" port and then goes out both 2" ports to the dual exhaust mid and rear silencers).

My current plan is to install a 2 into 1 downpipe from SNG Barratt #BSJR176 they offer for the S2 XJ6C, hoping the outlet is 2.25". This then somehow connects to the Magnaflow #337305 2.25" Front Cat. Then a short tube/adapter, somehow connecting to the single 2.5" port of the Magnaflow #338037. The two 2" ports of the rear cat then connect to each of the pipes leading back to the dual exhaust.
Does anyone have a picture or diagram of a working/original S2 XJ6 catalytic convertor system - an early one, with Stromberg carbs, to guide my exhaust shop’s custom work? Anyone who has passed Smog in CA with new CARB cats - what does your system look like? Are they these Magnaflows?
Thank you in advance for the guidance here!


some bit of the info is probably wrong … or weird:

In the US the SII cars came fuel injected and catalyzed prior to the introduction of the SIII in 1978.

I know that there were attempts of fitting unregulated cats to carbed SII engines before that date, but 1976 seems very early.

If your only hint at the original existence of the cats is the control light, it might well be limited to the EGR - which operates independent of the cats. I know a 1977 California car that was equipped with EGR, but without the cats.

BTW, the introduction of cats on unregulated engines was a step of despair. Jaguar knew the cats would get clogged very soon and considered them an item of regular replacement. So I don’t see much good in all of your efforts , as much as I applaud them!

Good luck


75 XJ6L 4.2 auto (UK spec)

Might help:

My Series II knowledge is limited but I think they might be erroneously combining Series II and Series III systems. Early Series III cars use a single converter; later cars had a second converter 2-3 feet downstream

Here’s a pic showing the single, forward converter on a Series III. I’ve never found an parts illustration of the downstream converter…but they do exist after 1984 or so

To clarify a bit

The 1978-79 Series II 6 cylinder cars were fuel injected for the USA market. Prior to that, carbureted.

The Series III was introduced to the USA in late 1979


Basically, Doug - if cats can be physically fitted they do the same with carbs or injected?

The various arrangements used OEM by Jaguar may just reflect stricter emission criteria - or indeed experience with clogging or whatever?

A central point with cats; they need to be hot to work properly - and may get clogged over time or too hot with too fat mixture and lack of cooling…

xj6 85 Sov Europe (UK/NZ)

The further away from the exhaust the colder. If flames shoot down the manifold and the mixture is rich the cat should be further away, otherwise it overheats even quicker. So the further away from the carbs, the better. Closer helps them get to working temperature faster. Was it really equipped with cats or did a PO just add the light or it was there for another reason…? Is it really just because of a bulb they saw?
I’d try to leave California if they are like that. Check the chassis number from Doug’s diagram.

Right. The converters don’t know or care if the engine has carbs or F.I.

But I’m no authority.

I know that all converters are not created equal; some are designed to react differently to the exhaust gasses. I don’t know the chemistry of it all.

I can’t say.

Emissions standards increased a lot in that era and manufacturers struggled with compliance. Converters were a quick-n-easy solution…but not inexpensive.

Yet not all cars had 'em. The parts illustration above for the Series II says “Not required for P.I. cars” and even my '76 TR6 has a placard that says “Non-catalyst”


The Series II parts illustration shown above shows a cat converter (CAC1237) and says “California/CDN/J/USA”.

I can almost guarantee that it would be easier to add converters than convince CARB that the car was never built with them…if that was actually the case. Exemptions and appeals are an arduous process. And CARB has accurate records of how the cars were built.

That would be pretty drastic…and Bob may have good reasons to stay.

Dealing with emissions testing is something that Californians have been dealing with for several decades. It can be a royal PITA but it’s just part of living there…which I did for 30 years.

Bob wants to get the car legally titled in California…which means it’ll have to meet xxx-requirements. There’s really no two ways around it.

The “good” of it all…or lack of it… is a different conversation :slight_smile:


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If the car was delivered with them, okay, make them happy. But if they get this far just because they see a light bulb leave while you can. I thought they would have added the converter only after the switch to fuel injection but if you say that the bureaucrats are correct then there’s no way around it and he has to please them.

My chassis # is 2J51560. Not sure if the diagram’s 2J52432 is the starting or ending #, but Doug’s point of trying to convince CARB w/o a cat is spot-on, and a cat will significantly lower my actual tailpipe emissions. We will have some margin for non-perfect engine condition and still meet the actual emission requirements. And I can’t leave CA - only about 4 of my currently 11 cars could make it to the border! Wanna buy a 1939 Buick Special survivor? Runs and drives… :grinning:
My new plan is SNG’s C44149 downpipe replacement ($132) and Magnaflow’s 2.25" front converter ($328), both on order this morning. With Doug’s diagram in hand, my local shop will take it from there…maybe $500 to manufacture & graft into my existing dual silencers? Thanks for the awesome guidance! I will update this thread with pics of the finished system, the cost, and my CA smog results! It may be a couple weeks…

This beautiful car was stripped of all its emission control systems - air pump, injectors, EGR, gulp, check valves, and every hose, pipe, bracket, clip, bolt and nut. And the Stromberg carbs. And maybe also a carbon canister/fuel evaporative control system. But it looks very pretty in the bay with her shiny SU HS8’s! As such, I believe it is illegal in all of North America, much less in CA. (New thread coming on the rescue status of this car’s emission systems, and a question of two…) A 700R4 transmission also was fitted. I have little doubt the PO didn’t also remove a catalyzed exhaust system, in the quest for performance.

Aha! Found and ordered 1976 Jag S2 XJ6 Parts manual on eBay. Will look for ROM, though my Haynes manual may suffice.

So there was a cat indeed and you would have to source + put a lot of parts back in… doesn’t sound like a good time, and you’ll lose a few horses too. No way to pass it as is but with cat? Looks good…

It might be able to be registered in Texas (where its 700R4 adapter plate was made) or another state or two, but not in CA and most others in the USA. If I claim it is a European car with HS8’s, it becomes labeled as a “grey market car” and I’m doomed in CA. Now I know why the price was a couple thousand $ below market for an XJ6C!

Thanks Doug!

Correct word order. “In the US the SII cars came fuel injected and catalyzed in 1978 prior to the introduction of the SIII.”

Doug’s copy of the parts catalogue may indeed help out in finding whether this car really had cats when it was first registered in the US.

Good luck


75 XJ6L 4.2 auto (UK spec)

Starting points:
2T54779, 2T60789, 2J52432

I’m not quite sure how to interpret those notations. Sorta looks like yours wouldn’t have a cat converter.

And I don’t know the difference between 2T cars and 2J cars

The parts catalogs are often quite helpful in various ways. But they’re not always 100% accurate, complete, or contradiction-free, I’ve discovered.

Some changes/info are documented in Parts Bulletins or Service Bulletins…and sometimes found in later editions of the parts catalog.

California, and some others, have a visual inspection as well as a tailpipe test. All emissions equipment must be present and accounted for.

Other states are tailpipe test only. Yet others have no testing at all, like Washington state. Others have testing only in certain specific areas/counties, like Oregon.

Technically speaking it is against Federal law to remove or defeat any emissions equipment. In reality this is virtually a non-issue as I’ve never heard of the Feds going after individual owners for this type of violation. They’ll go after businesses, though. There are a couple cases in process right now where businesses have (foolishly) bragged about how they’re defeating/removing emissions equipment.

Now that you mention it, are you sure it ISN’T a grey market car?


Grey Market car? Most likely not. She is sporting those oh-so-attractive thick, wide, chunky black plastic Federal bumpers, not the svelte chrome beauties like on Jochen’s '75 UK-spec. We also see the Federal tag in the door, showing #1560 of the 2J5xxxx LHD coupes was manufactured 11/75.

No catalyst originally? Perhaps not! Jochen knows of a California '77 with EGR and no cats; and Doug’s diagram seems to confirm the 2J51560 car is pre-catalyst; and if Jag XJ6 S2 catalyst usage co-incides with the '78 introduction of fuel injection, CA Smog will know it. (2T’s are maybe Japan?) CA Smog will not force me to install a cat if it didn’t come with one. We still have that pesky matter of the “Catalyst/EGR” warning light above the ignition switch… perhaps a bit of wood-grain tape, instead of fabricating a CA-legal catalyst system? :wink:

In all seriousness, new plan #3 may be to make my first pass at Smog w/o cats to get a baseline on tailpipe emissions, and see how my local smog tech reacts to a cat-less '76 Jag. Certainly I need to get her back to Federal emissions control, but that thread is coming.

And the warning that the manuals are not the gospel on these cars is well taken! Thanks all!

While the items mentioned was emission control related, Bob - they are not irrelevant for the cats either…

Unburnt fuel is unhealthy for cats, and during warm-up the engine is deliberately run ‘fat’, and generally also set to run a bit rich - more so with carbs. So, apart from rules and regulations, the other emission control is not without merit even with cats…:slight_smile:

But the engine itself is perfectly happy without any such external devises…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

I’m not too familiar with it but the extra fuel and the air pumped into the exhaust are like an afterburner helping the cat reach operating temperature as soon as possible.
I still believe EGR helps with consumption and mostly with NOX. And then there’s ignition retard and so on…

If it’s too rich and hot the cat will eventually glow bright orange and smell like fireworks and sulfur.

The engine is fine with all the equipment but it will run hotter, have less power and need more fuel. Doesn’t make it a bad car, all XJC are nice.


my understanding of the parts catalogue would be quite clear: the use of cats as described on page 1M 08L is limited to cars delivered to California from ## 2T54779 until 2T69450 (which is the advent of fuel injection). So the car with # 2T51560 would be pre-cat.

The “2J” nos. refer to 2-door Jaguars, LHD models starting with 50001:

Weird enough, the parts catalogue doesn’t make mention of the 2-door models. You may infer either that coupés generally were spared the cats (not very likely) or that the vehicle numbers were simply continued - no matter whether 2-door or 4-door. At least, that would be my line of argument, leading to the conclusion that your car is “pre-cat”.

Good luck


75 XJ6L 4.2 auto (UK spec)

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The air pump pumps only air into the exhaust manifold, David - to burn off excessive fuel delivered to a cold engine. But so it helps to heat up the cats - and protect them against unburnt fuel…

But the emission control addings, good for the environment, reduced effective engine power - which is why the US xk is weaker than the European unencumbered by them…?

xj6 85 Sov Europe (UK/NZ)

The air pump is piped directly into the cylinders on the exhaust side to drop cylinder temps in order to lessen NoX.

There isn’t a need to be worried about carb’d car’s running a cat, all remaining LBC’s were fitted with same by 1977, in the US.

In theory, an SU is marginally safer than an Stromberg with a stuck float causing raw fuel down the pipe, but the factory cat distance away from the carbs, even though in the upper portion of the downpipe, is plenty to evaporate the fuel before hitting the cat.

As opposed to say an MGB where the cat is literally sitting underneath the exhaust manifold.


This is a good representation of an unmolested ‘76.

Brain fart on my note, the cat is directly under the passenger compartment, and not in the downpipe. The injected cars had two, one in the downpipe and one under the passenger compartment, if I’m not mistaken.