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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
 

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nickm5 said:
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
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.
 

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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!?
 

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Geach said:
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!?
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
 

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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/
 

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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):thumbsup:
 

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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!
 

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

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

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Donati said:
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)

How did you come to this conclusion?
Marek
 

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kris said:
Finn, Who sad that High-flow cats give better flow than a straight pipe?
Geach said: (on the topic of de-cat)
"its not the best way to go and you are better off with sports cats".

kris said:
(8hp = atleast 10hp & 180k = 210+k ?? )What's this??? :)
Ok ok, maybe i was a little "hard" here, it was not ment to be taken too seriously :)
You said that you are sure Nick can gain atleast 10hp, and then told us that you have gained 8hp (8 = atleast 10?).
And this was accomplished on your 180K miles car.. while your sig. reads "210+k miles" (180k = 210+k?).

Come to the meeting of the European E34M5 scene at the Nurburgring this weekend, and i'll buy you a couple of weissbier, or give a pax-lap (if you are brave :wroom: )
 

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Finn,

If I could gain 8hp w/cats I'm sure he can gain 10hp w/o cats, Truth! :blink:

I had 180k miles on my car while dynoed

I wish I could go to the meeting :sad3: But in couple of years I'll move back to Europe and then we'll meet for sure :M5thumbs:

For now lets have a weissbier here :cheers: na zdrowie :M5thumbs:

Kris,
 

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So the crack is then that nobody really knows and its up to the individual??????

I also stated that i read here on this forum that high flow cats were better for you than losing them completely,not necessarily my opinion cos i havn't tried either,It was just what i have read! Seems a dyno test on the same vehicle with the different options of cat/no cat is needed? I'm quite willing to try if somebody sends me a selection of free flow cats?
 

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Hi,
I have removed the cats on my '91 3.6 and had them replaced with straight 55 mm tubes. I can definitely say the result is worth it, the car got perceptibly more torquey, pulls much better across the rev range, and last (but not least) sounds more like a superbike at higher revs ;). My cats were considerably clogged up and literally choked the car.

Regards
 

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Eryk_PL said:
Hi,
I have removed the cats on my '91 3.6 and had them replaced with straight 55 mm tubes. I can definitely say the result is worth it, the car got perceptibly more torquey, pulls much better across the rev range, and last (but not least) sounds more like a superbike at higher revs ;). My cats were considerably clogged up and literally choked the car.

Regards
I think i'll Have a go!
 

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The only thing I dont like about high flow cats from my experiences (on other cars than M5) is they make just about any car sound raspy. I had a 540i/6 speed with pretty much straight through exhaust but the stock cats and it sounded incredible, if you dont believe me listen to this sound clip of the car- http://home.earthlink.net/~twc9528351472/sitebuildercontent/sitebuilderfiles/reving.wav
A buddy of mine has a 540 also and had the completely stock exhaust but with high flow cats and the result was actually a very raspy sound. However the sound was pretty cool (reminded me of a ferrari but a bit different..). I had a 740il with the same M62 engine and I put identical exhaust as on my 540 but with high flow cats. The result was a terrible sound, it sounded like a a chevy pickup truck. It also didnt gain nearly as much hp on the dyno as the 540i and actually lost torque (540: 269rwhp/294rwtq 740il: 260 rwhp/255rwtq). From my experience with exhaust, the key is not to make a car too opened up to where it has not enough backpressure. You need this backpressure on naturally aspirated engines. A turbo car for example could run very wide open exhaust with large diameter piping because the turbo supplies the needed backpressure. A naturally aspirated engine will lose power at some point however if it doesnt have enough backpressure. And I realize race cars dont have cats or restrictive mufflers but they're tuned to run that way. If you don't tune your car to run like a race car it just wont be worth it. And if you do tune it for racing, well I dont think you'll want to drive it on the streets because of the noise and driveability/reliability. I think with wide open exhaust and high flow cats it would be too loud, and even if it did give you 2 hp could you justify it compared to your car when it wasnt ridiculously loud..
just my .02 cents
 

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redl1nerpm said:
I think with wide open exhaust and high flow cats it would be too loud, and even if it did give you 2 hp could you justify it compared to your car when it wasnt ridiculously loud..
just my .02 cents
You have much to learn about the sounds of an S38. :nono:
 

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redl1nerpm said:
The only thing I dont like about high flow cats from my experiences (on other cars than M5) is they make just about any car sound raspy. I had a 540i/6 speed with pretty much straight through exhaust but the stock cats and it sounded incredible, if you dont believe me listen to this sound clip of the car- http://home.earthlink.net/~twc9528351472/sitebuildercontent/sitebuilderfiles/reving.wav
A buddy of mine has a 540 also and had the completely stock exhaust but with high flow cats and the result was actually a very raspy sound. However the sound was pretty cool (reminded me of a ferrari but a bit different..). I had a 740il with the same M62 engine and I put identical exhaust as on my 540 but with high flow cats. The result was a terrible sound, it sounded like a a chevy pickup truck. It also didnt gain nearly as much hp on the dyno as the 540i and actually lost torque (540: 269rwhp/294rwtq 740il: 260 rwhp/255rwtq). From my experience with exhaust, the key is not to make a car too opened up to where it has not enough backpressure. You need this backpressure on naturally aspirated engines. A turbo car for example could run very wide open exhaust with large diameter piping because the turbo supplies the needed backpressure. A naturally aspirated engine will lose power at some point however if it doesnt have enough backpressure. And I realize race cars dont have cats or restrictive mufflers but they're tuned to run that way. If you don't tune your car to run like a race car it just wont be worth it. And if you do tune it for racing, well I dont think you'll want to drive it on the streets because of the noise and driveability/reliability. I think with wide open exhaust and high flow cats it would be too loud, and even if it did give you 2 hp could you justify it compared to your car when it wasnt ridiculously loud..
just my .02 cents
That WAV sounds very much to my old R32!!!

http://www.iptuning.com/r32zorst.mpg
 
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