Apart from torque and power considerations, personally I wouldn't remove my catalyst for a completely different reason, which is emissions (and that's what they are originally there for).
Without trying to look like a nerdy environmentalist, which I'm not, I do like the fact that it's possible to operate our cars without emitting more hydrocarbons, nitrogen oxides and carbon monoxide than necessary.
And I personally wouldn't change that for a few non-utilized kW or Nm more, which I don't use in my daily driving anyway.

Just my few cents, not all that can be done has to be done by all means.

 

By the same token I don't take 'Partick' (that's him, above left, he's a Tdvi) into my local city (Bristol) unless there are very good reasons. Twenty years ago I gave up a job in London (which I very much enjoyed, the job and the place, but believe me you could cut the traffic fumes 'with a knife' in London) because I started suffering from asthma (previous jobs had all been in rural areas). The X358 Tdvi is Euro 4 and whilst that's very good for not emitting particulates it's still not very good on NOx emissions. The 358 Tdvi doesn't have exhaust gas treatment ('AdBlue') which is what gets the NOx figures down on Euro 6.

I use my old manual g/box petrol Hyundai Getz for city driving... which I would change for a hybrid IF Hyundai they made one the same body size as a Getz and with a sunroof (ya' listening Hyundai ?)

 

I haven't had cats in a while now. I had the Hi-flow cats for a bit then had those removed. Both made a difference in power. Before I had my car tuned, I made 352/338 rwhp/tq on the dyno (with the other popular bolt ons and the cat deletes). They sell j-spacers, cat daddy's, etc to keep your CEL from coming on. My car is terrible on emissions and on gas mileage, and I love it. Wouldn't trade it.

So I guess it depends on your personal preference like many other things with our cars.

 

Hi Jazzyjags,

One of my next mods was going to be an upgrade from the standard cats to 200 cell cats as I don't fancy the hassle of having to swap out straight pipes come every mot,
But how much of a difference did you notice between the standard cats, sports cats and straight pipes?
Which step was the biggest difference?

Thanks for your help.

 

 

I got 200 cell cats fitted nearly 2 years ago, I noticed a power increase. It picked up nearly 2mph on the 1/4 mile. MPG is possibly improved also, I can get 35+ UK MPG on the motorway.
I don't use spacers for the sensors, as I have heard they mess up the fuelling and worsen MPG.

 

I did something similar to you Woofard.

Replaced the front resonator with an x-pipe but also have 200 cel cats.

I like the additional "noise" which is not noticeable at highway cruising speeds 70-85 mph. I get about 23-24 average mpg on a 450 mile trip.

However under hard acceleration my SC whine overpowers all other sound.

The only time I had any code was when I originally installed the mini cats that came with the replacement 200 cel cats. I also had clouds of smoke under hard acceleration.
Once I removed those everything was fine and never a code since then.

 

Thanks guys for that good advice, I did wonder about any requirements for jiggery poker of the downstream O2 sensors, I'm planning to replace all 4 for new standard sensors when I change out the cats as part of my preventative maintenance.
So far the combustion side of things seems very good, very clean.
HC=0
CO=0
O2=0%
CO2=15%
Which is all bang on, but will still be replacing sensors as part of maintenance.

I didn't realise the hi flow cats were so easily damaged so that's a very interesting bit of information, certainly means a keener eye needs to be kept for any hiccups with the engine.

All in all though some good confirmation as to the benefits of less restrictive catalysts.
I'll post once I've done the modifications, my biggest problem is access to a lift for enough time to get the exhaust off, cut, measure, swear, cut again and weld it all back up.

 

I did all my exhaust mods with drive up ramps with no real problem. I used an hydraulic exhaust expander for joins and clamps instead of welding with the intention of getting it welded later.

It took me several iterations of geometry to get it right.

 

I uploaded a Youtube video of a run I made a while ago where I forgot to switch off DSC. If wheels slip with DSC on with the LSD fitted it sometimes
seems to "bounce".
In this run I accelerated with pedal about 3/4 down. If the people walking were not there I would have started earlier.
In all the years I have driven this route this is the first time I have seen people walking!

 

I know this is an old thread but I can't believe there are so many misinformed people here.
First off, backpressure is NOT a desireable trait in an exhaust system EVER! PERIOD! It does Nothing for torque. Geezus!
It's often a necessary evil when tuning the length of a system using baffles. The timing of the sound waves is everything. Once they hit the end of the pipe, they do a 180. If these reach an open intake valve, the result is reversion. Reversion is bad and will result in a cloud of fuel coming out of a carb or throttle body at certain rpms and a nasty dip in torque will present itself. Ideally they're diffused well and carried out with the next outbound wave and never make it back to the engine.
You can have all the torque in the world with the right length of wide open drag pipes!!!
Cats are bad! They're restrictive as hell and also cause heat issues. It's no wonder y'all have had issues with brittle plastic parts!!! Cats are not your engine's friend. They are only there because of stupid government meddling. Same with routing your engine's breathing back into your intakes. Nothing good comes from that. Only bad.

 

Agree, what about just disemboweling the cats and simply welding them back up?