For the cherry on the top of my extra-power cake, I'm thinking about getting high performance catalytic converters. I've been told they can ad an extra 20-40hp, but might cause some error codes..

So looking for info/advice/experience - has anyone put high performance cats on ? how much power did they net? any codes? if they do trigger a code/engine light, then what?

 

Don't know of any codes, I believe the the censors are still in the factory place. Which CATS were you considering? Paramount Performance makes them for SC and XFR pretty pricy though.
http://www.paramount-performance.com

And a company called nouvalari-usa also makes them, but they only make for XFR and its a full cat-back exhaust. I'm pretty sure you can just order the CATS.
http://www.nouvalari-usa.com

Let me know what you have found. I'm very interested in this myself.

 

Wow, those are a bit more pricey that I would have thought, but not out of range.. I haven't considered any yet - just looking for more info on them.
My big concerns are throwing codes, and whether or not they will impact my California Smog Certification.

 

I have researchedthis already and the fianl out come by me and some of the OEM's who are making these 200 count high flow cats say it is just not worth the money vs the gains for our Jags. They said might as well just straight pipe it and save the money, and this is from the people trying to sell me the cats.

The best power package I have thought of for the XF was to straight pipe the whole exhaust from the stock manifolds back and either just keep the stock mufflers or swap those for those Varex units to control the volume when needed.

 

My suspicion is that this is probably correct, but not because the improved exhaust flow won't add any power. When exhaust flow is increased, you'll likely see a decrease in back pressure, reducing the amount of boost from the supercharger. In the end, it would either be a wash or marginally hurt performance. If someone were making an even smaller pulley, or if Stiegemeier could make a Snake Bite kit for the supercharger, you could get the boost number back on target. Sadly, it'll come back to tuning. There are several reputable vendors who will give you a canned tune, but that will fall short when you start changing out some of the less common components.

 

I think you've got that backwards. When exhaust restrictions are reduced engine airflow increases at the same boost pressure, and without affect on the boost pressure itself. The increased airflow makes more power. The ECU controls boost pressure probably using reference from the intake manifold, and will control an airflow by-pass to maintain maximum boost at ~10 psi above atmospheric pressure. Therefore any reduction in exhaust restriction will produce more engine power. I suspect that modern stock Jag cats are fairly low restriction already, and use of aftermarket cats would likely show minimal gains.

Bruce

 

No, you're right, assuming there's more boost to be had. With less restriction, you can expect to push more air through both the intake and exhaust valves, while they are open. In any case, I would expect slightly lower boost numbers, and a marginal change in power, if at all. I'd there was a way to adjust the ecu to deal with the change, the gains might be pretty decent. Unfortunately, it's anybody's guess.

I do wonder if expelling more exhaust gas would help to keep things cooler. I will also admit that most of my experience comes from far less sophisticated cars, so this may be a completely different game.

 

The ECU and TCU are indeed limiting power to enhance durability, and examining data logs shows them doing it by aggressively limiting boost below its peak on this particular engine most of the time, as well as limiting ignition advance. The weak link is likely the transmission's ability to handle torque. You can also see the effect of what the logs show on a dynograph, where the torque is flattened through the middle of the powerband instead of following a normal torque curve.

Bruce