dinosaur
Member
Registered: 21st Apr 04
Location: Bolton, not London
User status: Offline
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If you remove the catalyst its tricky because on the XE12 the cat sits close to the engine so it warms up faster. The location of the cat here is generally less restrictive than other cars with cats in the usual lower down location, although some cars like the Micra K11 use two cats one at the manifold one down below. 
The power gain I estimate would be pretty low, the cat is only going to be sapping power if its restrictive, which it probably is , but on the XE12 the velocity and amount of exhaust gases is probably not an issue on a pretty standard otherwise engine.
One important point....if Cats are so restrictive as everyone thinks on these little Vauxhall engines....the exhaust gasses would never get out the engine and down the pipe they'd just go down the pipe hit the cat, and get back into the engine causing dilution of the new inlet charge. Hence the need for high performance 'extractor' manifolds and stuff.
This was a prob on old engines with crap flowing exhaust manifols and it would still be an issue even on cars equipped with EGR and all other emmision equipment.
Then you also have to find a place for the lambda sensor, some aftermarket manifolds let you screw it to them.
The restriction on the 1.2 16v and most other Vauxhalls is the design of the inlet manifold and induction tract. Hence the purchasing of items like Velo Torque tube.
According the Dbilas site replacing the XE12's inlet with one of theirs give 23 bhp, which would back up the fact the engines are restricted.
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