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trying to establish still the decat pipe theory
agree its not really legal but if they are sold openly then if using one except mot day are any bhp gains to be had in any way
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They are perfectly legal providing the car still passes the emissions test with it on - there is no requirement to actually have a cat, but it's hard to pass the test without one. Saying that, A few of my cars have passed fine without one.
Don't expect massive gains, a few BHP at best, if anything. You shouldn't lose any power though.
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Don't expect massive gains, a few BHP at best I think that depends entirely on the engine. Some more powerful engines actually gain quite a bit of power from a de-cat. It's all relative to the original power I guess....it probably equates to a similar % increase on a smaller engine? Figures are ficticious (SP?) and just for illustration/example purposes: Lower power engine = 75bhp with de-cat = 79.5bhp 4.5bhp = 6% increase Higher power engine = 275bhp with de-cat = 291.5bhp 16.5bhp = 6% increase Like I say, the figures are just made up for illustration purposes, but the BHP increase can become more significant with more powerful engines. It also comes down to how restrictive the original cat was, what type of exhaust you have beyond etc..... I would only ever fit a de-cat on a pre-93 car - only because I can't be fagged with changing it every year for the MOT. |
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You will notice a much bigger increase on turbo charged cars, rotaries tend to find the biggest gains. (The removal of the restriction caused by the CAT will enable turbos to spool faster due to less back pressure, the increased available volumetric efficiency in the exhaust will enable the engine to push through more gases - be warned this can lead to boost spikes in turbocharged cars, so ensure you have a good boost controller.)
A 3" DCAT exhaust system and an FCD saw a 50bhp increase in one of my old TII's...
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FlickR: FC3MRC
Youtube: BrettMRC
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I suppose I'm stuck in small hatchback world, where a few hp is 6%, lol.
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Yeah I was about to say, my ca18det 200sx had a de-cat pipe and it made a nice difference, think its more suited to turbos but stuill, if you can get a couple of bhp by junking a curse word factory bit then its gotta be worth doing! Plus, I think in the right place you can get some cash for an old catalytic converter? Ive heard that jewellery can be made from their innards!! Actually anyone know anymore about that as I have the 200sx cat sitting in the garage, wouldnt mind swapping it for some cash! Its a bit big for an earing plus it doesnt suit me
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Mar 18, 2009 12:15:02 GMT
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As already said if you did fit a decat pipe to a post 93 car, you'd best hang onto your cat in case you have problems with the emissions test come MOT time and need to refit it.
Scrap men give good money (£20ish last time I checked) for cats as they've got small quantities of platinum in em.
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Last Edit: Mar 18, 2009 12:15:33 GMT by whitbytom
1967 Morris Traveller 1971 Series IIA Land Rover 1991 Golf GL 4+e 1992 Corrado G60 1986 E28 BMW 528i |
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Mar 18, 2009 13:56:00 GMT
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A lot of engines will only make more power if remapped / tuned to suit! It's fairly rare for a car to make anything other than more noise by just removing the cat. A typical upgrade for the Impreza STi is a decat exhaust, better filter and remap and that can gain somewhere in the region of 60bhp! Up from 278 to around 330-340. To do it properly will cost you in the region of £800 or Prodrive will take around £1700 out of your pocket to do it for you  |
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1997 TVR Chimaera
2009 Westfield Megabusa
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Odin
Posted a lot
Posts: 1,406
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Mar 18, 2009 16:21:12 GMT
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There's a very handy test done using MGFs plucked from my bookmarks here. Makes for interesting reading! |
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Mar 18, 2009 18:53:09 GMT
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thanks interesting info
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J curse word tends to have good cat flow, gains are between 1 & 2 bhp on Civ type R's and SR20DE's you do get more noise though  |
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Nissan Laurel SOLD  BMW E34 Diesel SOLD Toyota Soarer 4.0 V8 SOLD Audi A4 1995 TDI SOLD Peugeot 205 1.9 TD SOLD Lexus IS300 SC |
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Mar 19, 2009 10:34:56 GMT
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Can be great on 80s/early 90s cars too where cats were still a relatively new thing and hence horrendously restrictive, especially if there's multiple instances of them.
My old pre-90s C4s had 3 (!) catalytic convertors, for example - two primary ones and then a huge secondary one, absolute madness. Really quite restrictive and a good few MPG gained, at least, from their removal. Ran better too (although this is probably more due to throughflow deteriorating with age but still).
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qwerty
Club Retro Rides Member
Posts: 2,416
Club RR Member Number: 52
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decat pipe more or less powerqwerty
@qwerty
Club Retro Rides Member 52
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Mar 19, 2009 14:54:12 GMT
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My experience with de cats is limited to modernish french warm hatches, I don't know if I gained much power but the power delivery was much smoother. In fact the engine seemed to rev a lot smoother while under load.
If I can ever be bothered I'll junk the Catalyst off the Polo as its a 92 so I don't need it, and if I don't need it and can save a bit of weight and get better MPG I might as well get shot!!
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Last Edit: Mar 19, 2009 14:55:35 GMT by qwerty
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B-8-D
Posted a lot
down to one car!!
Posts: 4,038
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Mar 19, 2009 15:41:20 GMT
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senator 24v improves by 23 hp apparently...
not mine tho so just heresay / secondary info....
ive never had anything with a cat tbh only old cars so I dunno
si
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Last Edit: Mar 19, 2009 15:41:53 GMT by B-8-D
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Mar 19, 2009 18:50:25 GMT
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do you need a cat on L reg 93 cars
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I always see improvements on my dyno from de-cats. Not massive on some cars as previously mentioned. There are some very good sports cats on the market that are offer an MOT-able option whilst not being anywhere near as restrictive as a stndard cat
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sonds convinciong to de cat
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MartinC
Part of things
Don't like stretched tyres, very low profile tyres & I think a car CAN be too low. Perhaps I'm odd.
Posts: 935
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I removed FOUR cats from my Lincoln. The new exhaust was also made from bigger pipe as the original was quite small.
performance at low RPM (torque) was predictably slightly worse than before, but after that.... OH YES !!!
A heck of an improvement. No remapping or chipping or anything like that.
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1937 Standard Flying Twelve
1943 Bedford OYD
1947 Cadillac Fleetwood Sixty-Special
1954 Hillman Minx MkVIII
1956 Austin A30
1957 Vauxhall Victor Super
2001 Chrysler 300M
2002 Rover 75 Connoisseur SE Tourer
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Mar 24, 2009 12:46:04 GMT
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K plate or later will need a CAT. Earlier cars designed with a CAT will probably still need it for the MOT emissions check.
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FlickR: FC3MRC
Youtube: BrettMRC
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Sept 28, 2017 18:52:22 GMT
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Probably replying a bit late now but I’m thinking of doing a decat on my 2005 Hyundai coupe 1.6 but there’s some people saying I’ll lose power then others saying I’ll gain a bit or stay the same. Anyone have any info,
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