The catalyser seems to be the most misunderstood component in the exhaust judging by the antics of some owners.
It's a common strategy to remove the substrate - this VX220 N/A owner is in the middle of doing this on the downpipe bolted to the manifold, hoping that he will release some bhp. Reducing the back-pressure innit! This one is a metal substrate and it's tough to hack it out. Unfortunately, where you really need the gas-speed to be at its highest, he's created a large void which slows it right down - not the best feature to encourage scavenging at the exhaust port.
All the Toyota-engined cars use the same body (mantle) and ceramic substrate for all the different motors - 4 & 6 cylinder.
Here is what the internals look like on the V6 motors which have them fitted -
You can see it's a very restrictive honeycomb - 600cpsi (cells per square inch).
The log manifolds (headers) on the V6 use these UTC's (Ultra Thin Catalysts) to help the car pass some very strict worldwide emissions tests.
The whole design is a serious block on power output and with increasing power outputs on each new V6 model, they are under a lot of supercharged stress. For instance - don't even think about retaining these manifolds on a TVS1900 install!
Looking at the 4-cylinder motors, the later 2ZR motors seem to destroy their factory catalysers very quickly. Particularly with track use. If you look inside the factory manifold you will see the first Lambda sensor (the one that controls fuelling) has had to be shielded from the stresses of supercharged gas-flow.
If you can, it's always best to move the first Lambda sensor further down the pipe and use a wiring extension. Supplied with all 2bular 2ZR manifolds.
Same on the V6 installs. Getting rid of those log manifolds and their vulnerable UTC's (Ultra Thin Catalysers) is a great move for more power and torque and moving the first Lambda sensors to the downpipes means the sensors are not toasted so regularly. Whenever the factory manifolds/catalysers are removed, it's usually found that the first sensors and their wiring are crisped to perfection. I strongly recommend fitting new 1st lambda sensors when the 2bular EPK is fitted. You can see the 2nd sensors are fitted on the exit cone of the big HJS HD catalyser.
The owner of his new 111R was told he had a 2bular 4-2-1 manifold + catalyser already installed. Unfortunately, the catalyser wouldn't pass an MoT and he sent the offending item to me for appraisal. Sadly, he didn't have a 2bular 4-2-1 and he didn't have a 2bular catalyser. I was actually working on one of my catalysers when it arrived and took this pic -
Those tiddlers (I refuse to call it a 'catalyser') were very popular with certain aftermarket suppliers a few years ago. Cheap and nasty pieces of kit - but some people are 'cheap' and thought they had bought a bargain!
A very irate supercharged 2ZZ owner contacted me recently. His 7 month old Hangar 111 catalyser couldn't pass its MoT. It's always difficult to tell by looking at a catalyser if it will 'work'. Only when it can't catalyse and fails an emissions test do you find that out - and then it's too late! Here is the Hangar 111 cat -
Compare with the 2bular 2ZZ-GE catalyser -
The first thing that leaps out at you is the large bore of the link pipe from the OEM manifold to the catalyser itself on the Hangar 111 design. It's 3" diameter! So when you're looking for a high gas-speed at the exhaust port, this large bore slows the gas-speed right down. Not good for scavenging and consequent damage to performance. Mind you - it's very easy to swage a 3" pipe out to the required diameter for the doughtnut gasket! That strange bent flange plate? No idea.
The 2bular design has a fully-welded flange which allows the same dimension as the OEM. So the springs have the same operating length. I use a reducer to bring the gasket cup down to 2.5" diameter - same as the rest of the system - maintaining a high gas-speed from cylinder head to tailpipe.
Looking at the other end of the Hangar 111 cat, it uses a 2.375" diameter pipe for the exit. If you want your catalyser to operate efficiently, you don't want such a big difference between entry and exit pipework. Hangar 111 have had to swage the pipe up to 2.5" to fit to the silencer entry.
As stated earlier, it's not possible to evaluate the quality of the actual catalysing substrate itself - and this Hangar 111 example failed its first MoT. I have been using the German HJS catalysers for almost 5 years now. A quality component with a good weight of the rare materials needed to actually do the catalysing. Expensive - but it will do its job for a lot longer than 7 months.
You see the 'HD' tag on the big 130mm HJS catalyser below? That stands for 'High Durability'. The 200cell metallic substrate 'brick' is hi-temperature brazed to the shell (mantle). During track or race use, a lot of raw fuel can hit that glowing substrate (over 600deg C) and the brazing can melt. The brick is now loose inside the mantle and the gas-pressure on a supercharged install can push it down the exit cone and it forms a very effective plug. Melted pistons follow very soon after.
If you look closely you can see three compression indents in the middle of the mantle. Used to be a single indent but now three. This feature can hold the brick even after the brazing has melted - and the catalysing continues. Very clever - very HJS.