nickm5

hi , this is my first post on this board as i have only just bought nice 3.6 m5 . I was wondering if there is any gain in removing the cats from car , as it is a 1990 model cats are not a legal requirement . I would also consider a chip or remap to make the most of the change . I have removed cats in the past and it has made a difference , has anybody done this to an m5 before ?! . If anybody can shed any light it would be appreciated .

Thanks

nexus1972

I believe you will still need your cats as I thinbk if they were originally fitted to a vehicle prior to being a requirement they must be there at MOT.

Of course MOT testers vary in how closely they look at the charts detailing which cars do or dont have cats fitted prior to the requirement.

Geach

Thinking of doing the same thing myself, also on my 1990 3.6. Theres a good chance of getting away with it for the MOT. If you go ahead let me know how you got on, I have read on this forum that its not the best way to go and you are better off with sports cats????? But if theres a performance gain to be had its got to be worth doing!?

farrell

Fellas
Things have changed with Mot testing now. It comes under VOCA & the new monitoring equipment now required in test centres will allow real time checks of vehicles emissions & Brake mean efficiency test. It was planned for this to go live this yr.
The test will also log your plate & details with other interested parties for warrants & could also check that the vehicle is insured in future or no certificate.
The onus on the tester who is still licenced personally will make many comply with the letter of the law.

I also interpret the rules on catalysts fitted before the transition period 1992 -1993 to be that if the vehicle was fitted with catalysts by the manufacturer, it should be tested as such.

There are small relative gains to be made from decatting but its not much as these things are high flow low resistance underfloor units coupled to a very efficient double skinned exhaust with the most efficent type of muffler.
The Absorption style muffler uses baffles radially mounted round a perforated centre pipe which the gasses pass through mounted within a single muffler chamber. The packing is a basalt packing compound.

The reflective muffler which many road cars are fitted with, has two chambers & the gas does not have a direct flow path. It takes a staggered path through the muffler with inlet pipe & outlet pipe mounted next to each other & staggered so flow has to double back on itself. Good noise absorption but poor gas flow result.

I would not mess to much with the std exhaust as it is far from standard compared to most.
I do accept there are some gains to be had with decat & eprom remaps but there have been many a melted piston along the way with this path.
There is no knock sensor as std within the cylinder head so an afermarket knock sensor system fitted to each cylinder would be advisable.

I expect to now have the fellas who have decatted & fitted stainless exhausts plus eproms to be coming after me to tell me that the world is round , not flat.

No offence meant Guys. If it works for you, its cool.

Regards
Farrell

Marek

About 12 years ago Frank Fahey of San Diego was selling a high quality track pipe, replacing the cat. He really believed that for track applications M5s greatly benefit from shedding the cat. Considering his experience I have no doubt that he is correct. If anyone doubts the benefits should weigh the pipe and the cat. The weigh difference is at least 20 kilograms. Besides that the car runs much cooler. The disadvantage is that the car is a bit louder. I think that there is some power gain as well. Hope that helps.

http://www.frankfaheymotorsports.com/door/

kris

I'm SURE that you can gain at least 10 RWHP

In my experience, I've replaced my stock cats with small Hi-flow cats & my Dyno #s went from stock 274 hp & 237 tq UP to 282hp & 244tq AT THE WHEELS ( with 180K miles)

__________________
'93 M5 DaytonaViolett 3.6L 225+K miles

Cyrus

Ive had 2 M5's at the same time both in mechanical good condition. One car has the origional System and the other a custom built stainless with no Cat's.

You can defintaley feel a difference in top end power above 5500 rpm. However this is the ONLY place you can feel it.

Its upto you if you want to pay money, risk having MOT problems and only have a gain in a very narrow rev band. I personally would not bother.

If you want better performance just get Emerald fitted (hence removing the MAF) for around £1200 which includes setup and mapping. I have no idea how the resonator flap will work though!

Donati

You guys are so funny

High-flow cats give better flow than a straight pipe?
8hp = atleast 10hp & 180k = 210+k ??

Mvh Finn
(will install magnets on the fuel-line to get unlimited hp)

kris

Finn, Who sad that High-flow cats give better flow than a straight pipe?

(8hp = atleast 10hp & 180k = 210+k ?? )What's this???

__________________
'93 M5 DaytonaViolett 3.6L 225+K miles

Marek

How did you come to this conclusion?
Marek