De-cattng . What are the benefits?
Discussion
I'm sure our resident techies will confirm but doesn't the removal of the cats improve the outflow of exhaust, releasing a bit of power? In practice I can't say I noticed any difference at all in mine.
But it did cost a few quid and of course it's not just cat removal you need to take care of, there's remapping to do too.
The main difference is noise. Mine's been done, couple with a 404 cam and other bits and on idle it is not as nice a sound as a standard 500. But when it has a few revs on it and comes on cam, the sounds is unbelievable - and at last testing a fair bit in excess of 110db
As you're in Herts, why not pop round and have a listen. I'm in WGC.
AF
But it did cost a few quid and of course it's not just cat removal you need to take care of, there's remapping to do too.
The main difference is noise. Mine's been done, couple with a 404 cam and other bits and on idle it is not as nice a sound as a standard 500. But when it has a few revs on it and comes on cam, the sounds is unbelievable - and at last testing a fair bit in excess of 110db
As you're in Herts, why not pop round and have a listen. I'm in WGC.
AF
Thanks for the offer Angus, I may well take you up on that at some point 
On the one hand I wouldn't mind making the Griff a bit louder for vanity's sake, but on the other I am keen to keep taking her out the track and would hate to fall foul of any noise limits.
Hmmmmmm, decisions, decisions....
On the one hand I wouldn't mind making the Griff a bit louder for vanity's sake, but on the other I am keen to keep taking her out the track and would hate to fall foul of any noise limits.
Hmmmmmm, decisions, decisions....
I saw (and heard) a decatted Griff on Sunday...sounded fabulous, it had a real crackle in addition to a louder rumble! However, on a journey the noise would become very tiresome for me after a while...I must be getting old! 
IMO I doubt if the primary cats reduce gas flow much so simply removing them should have little or no mprovement in performance.
IMO I doubt if the primary cats reduce gas flow much so simply removing them should have little or no mprovement in performance.
Toffer said:
I saw (and heard) a decatted Griff on Sunday...sounded fabulous, it had a real crackle in addition to a louder rumble! However, on a journey the noise would become very tiresome for me after a while...I must be getting old!
Yes - this is a good point. A group of us drove out to Oxford for lunch on Sunday. I took a passenger. We had to shout to each other to be heard so conversation was no very easy. we took the motorway on the way back and after an hour on the M40, M25 and A1 I was really ready for a quiet and dark room...
The crackling and popping and occasional spit out the back are great fun in small doses. But it does limit the fun in other ways.
I did manage a monster pop on Marlow bridge on the way to Oxford. Scared the crap outta the tourists!
I just read the bible exhaust chapter last night (couldnt get to sleep! Just kidding shpub ).
Anyway, the general summary was that if you like the power you have just leave it alone unless your prepared to make other changes.
(Although this may have been just for silencers).
Also Griffs in the channel islands dont have Cats regardless of age. Must put a higher premium on them.
). Anyway, the general summary was that if you like the power you have just leave it alone unless your prepared to make other changes.
(Although this may have been just for silencers).
Also Griffs in the channel islands dont have Cats regardless of age. Must put a higher premium on them.
Just got mine back having had pre cats removed. Already had sports exaust. Negligeble difference in power & torque but much louder !
I set off 2 car alarms on Sunday which I never did before. It also crackles & pops big time on overun. If they dont see me coming they will certainly hear me !
Dont think I'd go any further as i'm there with the noise now.
I set off 2 car alarms on Sunday which I never did before. It also crackles & pops big time on overun. If they dont see me coming they will certainly hear me !
Dont think I'd go any further as i'm there with the noise now.
Interesting. My 2p worth:- Apparently when you have the pre-cats removed, you should have reverse cones fitted in their place. (ACT do this on an exchange basis.) It helps prevent back pressure pulses shooting up the primaries which help power. You should see 4 -5 bhp, but may require a remap to get the benefit. Many of these mods are pretty useless unless you do. I would recommend a Mark Adams chip and rolling road session, which gets expensive if you're going to have this everytime you make a change.
The precats do not affect emissions on a warm engine (as MOT'd) only on a cold engine.
At a recent dyno session (read thread elsewhere) there was my 500 with standard headers, just an emptied silencer, Tiny's with a sports silencer and no precats and Guillotine's with bugger all.
His was loud with a capital 'F'. Tiny's was quieter than mine, which has a harder edge.
I have some ACT track day silencers which I will be using at Hullavington on the 28th. Hopefully they will keep it quiet enough. Guillotine will be there too, so it will be interesting to see how he gets through the sound check, although he's been before.
The precats do not affect emissions on a warm engine (as MOT'd) only on a cold engine.
At a recent dyno session (read thread elsewhere) there was my 500 with standard headers, just an emptied silencer, Tiny's with a sports silencer and no precats and Guillotine's with bugger all.
His was loud with a capital 'F'. Tiny's was quieter than mine, which has a harder edge.
I have some ACT track day silencers which I will be using at Hullavington on the 28th. Hopefully they will keep it quiet enough. Guillotine will be there too, so it will be interesting to see how he gets through the sound check, although he's been before.
Well guess what...I am finally having this done after investigations into my emissions problem (thread here) turned up a manifold that thought is was a part of the cooling system. The water has pretty much completely destroyed the pre-cat so the simplest answer seems to be to get rid of them!
I can't wait to get her back now, faster and louder....
...the wifes going to hate it
I can't wait to get her back now, faster and louder....
...the wifes going to hate it
Austec did mine when the cats melted blocking the exhaust. I was down to about 130BHP! Decatting not only released a HUGE wodge of power (that really should have been there in the first place) But the noise......oh my God the noise.......you'll be putting the clutch in a revving as you go through tunnels....people scamper for cover 2 miles away thinking that the apocalypse is coming.
RichB said:
I de-catted my Griff, but with hindsight I think I preferred it with the cats in. The exhaust note was louder, but not as musical and, if anything, it felt slower.
Presume you mean is louder and feels slower with the cats out? Rich...
Yes.
How's that for a quick response!
Just spoke with Austec today re pre-cat removal. They do before and afters on their rolling road and they advised the following:-
1)No increase in BHP
2)Approx 15lb of torque increase 'snap throttle response'
3)Reverse cones not neccesary
4)7 hours labour
Shall I, shan't I
Oh go on then 
1)No increase in BHP
2)Approx 15lb of torque increase 'snap throttle response'
3)Reverse cones not neccesary
4)7 hours labour
Shall I, shan't I
Oh go on then Higgins23 said:
If you remove the Cats, how difficult is it to reinstall them before your next MOT ?
I wouldn't mind knowing this as well. I'm currently deliberating on spending about 2-3k on upgrades at Austec in the new year and was considering pre-cat removal as part of this. That as well as Mark Adams chip/RR session etc.
Also I'd be interested into the pro's & cons of a total decat? Although as I already have no silencing in the exhaust that could be taking the p*ss a bit. Call me a chav if you want but I kind of like the idea of the odd flame shooting out the exhaust now and then!
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