Decat the M5

[zarnd]

as the title suggests. Thinking about taking the cats off and running some straight pipes instead. Anyone ever done this or know anyone who has done it? I have asked on M5board and had a search and no one has seemed to have done it and they are all telling me it;'s a bad idea even if i leave the pre-cat sensors in place.

Also spoke to CA and looks like the decat pipes that they used to supply aren't being made at present, and MOT emissions shouldn;'t be a problem either!

cheers

[paris]

you will have codes thrown about cat efficiency and you will fail the MOT. And you will pollute the environment more.

[zarnd]

you will have codes thrown about cat efficiency

that does bother me, will it produce a warning light?


and you will fail the MOT. And you will pollute the environment more.

that doesn't both me, and MOT is not a problem. They can be put back on for it

cheers

[paris]

When I had a cat efficiency code (oil contamination) the engine light went on as well. Guess you will have one as well on the M5.

Why don't you contact Hans @ ESS and ask if they can reprogram your ECU to disable cat check?

[zarnd]

hmmm...thanks for the info. Don't want to go down the road of having the ECU reprogrammed as the car still has BMW warranty on it, the exhaust si no longer covered after July this year and if there is a major problem the CAT's could be put back on for it for example.

I was hoping that it may just be a simple procedure without warning lights and getting things reprogrammed, but i suppose if that were the case then more people would have done it by now and as of yet i haven't found one person who has done it!

cheers

[peppernick]

You are likely to lose more back pressure and hence, torque. I'm sure with your more free flow exhausts you have noticed the throttle feels softer at lower revs?

Also, with your current exhaust set up, it will be obnoxiously loud.

If it's the added noise you crave, I can understand the urge. Just like when I had to try out the GruppeM exhaust on my M3. But the novelty wore off very quickly.

[BMW JAY84]

Alex you got to be kidding. If your exhaust gets any louder you'll be tailed by environmental health !!!!!!

[Doc Matt]

Alex you got to be kidding. If your exhaust gets any louder you'll be tailed by environmental health !!!!!!

I've actually got a headache just thinking about it :eek: :eek: :eek: :D

[zarnd]

You are likely to lose more back pressure and hence, torque. I'm sure with your more free flow exhausts you have noticed the throttle feels softer at lower revs?

Also, with your current exhaust set up, it will be obnoxiously loud.

If it's the added noise you crave, I can understand the urge. Just like when I had to try out the GruppeM exhaust on my M3. But the novelty wore off very quickly.

i would like it louder, and it is loud at the moment and obnoxiously loud would be a laugh for a day or two but would probably spoil the driving experience!

sounds like it is going to be causing more trouble than it's worth.

looks like it is going to be race cats and headers for £3k!

cheers

[peppernick]

looks like it is going to be race cats and headers for £3k!

I would spend £1500 on a shorter rear diff. You'll feel the effect more. I've experienced Tin's M5 with a shorter ratio Kellerners rear diff. What a change!

Even during cruising, you still pull reasonable revs in 6th.

[zarnd]

I remember talking about it at the 'Ring in the Pistenklause in a beery haze! Have had a brief look at the Kelleners website, and couldn;t see anything on there about a shorter ratio diff, will drop them an email.

Half of me would like to listen an experience Tin's M5, the other half doesn;t as i will be straight to Germany i think!

Would a shorter ratio diff affect the top speed? A pedantic thing to maybe worry about i know. Pretty sure they do a remap/chip for removing the top speed limiter etc...

going to have a proper look at it this weekend i think, and contact them

thanks nick.

cheers

[peppernick]

Depending on ratio, it will drop the top speed by 10-15MPH (which is way after the limiter cuts in anyway).

But the increase acceleration, I guarantee you'll be grinning from ear to ear. I was laughing my ass off just being a rear passenger in Tin's car.

It may not even be that expensive. It's justa crown gear swap. The actual diff itself is re-used.

[zarnd]

found it on Kelleners web site, and looks to be around 2400 euros for the diff, but as you say if mine is reused then it will probably be cheaper!

cheers