Cat vs Decat

realscot

realscot

realscot

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Joined
6 Nov 2005
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2,317
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Aberdeenshire
I just stuck my CAT back on my car yesterday for the MOT today, failed on a cracked drive shaft boot!! would you believe it. Bit of super glue and some black sealer and we're back in action.
Anyway when I put the cat back on I could actually feel the performance difference, i didn't think there was much difference taking it off but now its back on its definitely noticeable. The other thing I've noticed is that I have a much louder induction note since putting the cat back on? Is that because the engine is having to work harder to breath out? I'm not really sure, but i figured someone on here might manage to explain that one for me.
I miss the tinny rip that the vtec makes when the cat's off, so it's coming back off again tomorrow if i can be arsed lol.
 
slighty off topic but does it take much to get them off and on?
got my de cat sat at home that was put back on for mot and the dude stated some silly price to put it back on, seems like it should be quite simple?
 
well on mine it was 5 bolts and a little bit of exhaust sealant paste. Took about half an hour since I had to use 2 trolley jacks to just get under my car. A reasonable garage shouldnt really be charging more than £20 - £30 for doing it. The fact that you have to change them off and on again every year means the bolts dont really get a chance to rust over propperly, but then i did swag some stainless nuts and bolts from work lol.
 
Dreadi said:
slighty off topic but does it take much to get them off and on?
got my de cat sat at home that was put back on for mot and the dude stated some silly price to put it back on, seems like it should be quite simple?
Click to expand...

on a Civic? There's 5 bolts, atleast 4 of them will be rusty or seized:p
 
silversurfer said:
Cat alters torque mostly I think, it'll move the rev counter quicker and feels less sluggish
Click to expand...

Yeah that would explain how it feels faster without it, but what about the massive increase in induction noise? its like i didn't have a cold air intake before with the cat off, and have one now with the cat on.. it really is that much different.
 
Anyway, there's definite gains to be had by removing the cat. It's a cheap mod.

In my case, after the MOT I didn't bother putting the de-cat pipe back on as the exhaust sounded much nicer with the cat on, it made a raspy noise de-catted. I've not noticed it being down on power but I'd expect it to be 3-5hp down if I was to dyno it.
 
cheap if you get it done at the right place. A friend has an Evo 8 FQ320 and he was phoning around for prices on a decat (custom making/fitting) and it ranged from £80 to £350, and they were all just to replace the cat with a stainless pipe. It cost me £50 as a mate worked at a garage that did powerflow exhausts.
 
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Copper grease comes in handy for things like this.

You'd expect it to burn off, but it actually stays in the threads.

I recently swapped my lambda sensor and was expecting it to MEGA tight (swapped it last year). It came out with very little effort and almost sent me flying into the hedge behind me :o
 
Decatted my cooper the other week and i cant say i can tell any difference in power, there's has been more of a change in exhaust tone it isnt any louder but its a bit sharper you can here a bit more engine then air woofing around.

The engine is still running in though so its going to be a while to see how things progress.

There isnt a great deal more i can do to the engine now for more power without dumping another couple of grand :-(
 
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