There is a sensor before the cat, so you donīt have to worry about any ECU screw-ups if you remove it, which is not the case with the e39 M5...
If the sensor was after the cat, youīd have to install a small resistor in order to trick the ECU into thinking that itīs still there.
I took off my cats too, the car got a lot better IMHO, and the exhaust noise is even nicer.
Hi,
would appreciate some more info about your cat-removal experience... Did you by any chance dyno the car before and after this operation? Did you have replacement tubing made to fit in place of the cats? Or have you replaced a larger section of the exhaust system? Has the car become considerably louder? Do you feel a significant torque increase, does it pull better in lower revs?
Regards
Eryk
__________________ Eryk
'91 E34 ///M5 3.6 diamantschwartz, black leather, electric seats, automatic A/C, headlight/halogen wishwash, skibag, electric sunroof, M Coupe 17" wheels for summer, turbines for winter (both sets 9"/255 rear), Supersprint rear muffler, cats removed, white front indicators
Me and a couple of other M5 owners have already removed the cats. Two of them did it right next to a dyno jet. There is absolutely no loss in torque or horsepower through out the whole rev and torque range. The differences are a slight hp increase at high revs (like 2hp max) and most importantly, when you see the torque curve on the graph, you can notice that right after the engine reaches peak torque, the line on the graph does not fall off as much as it does with the cats on. This means that at high revs the engine has greater torque until it reaches 7250RPM.
The exhaust sounds a little louder and a little nicer, it is far from being annoying or obstrusive though, so donīt worry about that.
I put two aluminum replacement tubes in place of the cats in the exact same diameter as the rest of the tubing. Maybe a little bigger, but very little. These tubes were welded to the original tubing, between the screw joints, meaning that you could have someone make another set of tubes with the cat, and just screw it on to the original exhaust tubing in case itīs needed for an MOT for example.
You can clearly feel that the car is easier to drive in traffic especially when letting go of the clutch in 1st gear (less resistance from inertia), and you can feel that the engine feels "more free" than with the restrictive cats (have you ever seen what the cats look like inside? Itīs like a cork!!), meaning you can cruise better at low speeds in a high gear since there isnīt any backpressure resistance coming from the cats. Which means that you donīt have to depress the throttle pedal as much to keep a high gear at low speed.
Hope this helps.
Cheers,
Pedro
__________________
1995 BMW M5 Schwarz II Shadowline
Dr. Schrick camshafts
UUC Short-shifter
We call them "track pipes" in the US. A friend with an M6 dyno'd 20hp more to the wheels with the cats removed!! Although the M6 has a more restrictive exhaust than the E34 so I don't believe I will realize that kind of gain. He just made me one out of an old M5 exhaust system but I will primarily just run it on the track. He is also going to build a system using high-flow steel cats to see how that works. In any case, you will have to install the original cats to pass smog in California. I am really looking forward to a bit more growl from the engine.
__________________
Kevin Kelly
91 M5 Alpine White/Black
(D'Sylva Chip, Dinan springs w/Konis, camber plates
Racing Dynamics sway bars, 18" BBS RC's
345mm brakes)
'95 M3 Avus/Dove, (Conforti CAI/software, 24lb inj., GC suspension), new track rat.
I picked up about 10mph on the back straight at Sebring when I replaced my cat with a RD resonator about 4 years ago.The sound with the B&B is quite loud-setting off alarms in open parking lots as I drive by slowly.
I've had no issues going catless.
Last edited by Mel A; 11th November 2004 at 04:29.
Think I'm right in saying that having a Cat isn't a legal requirement - it all comes down to whether the car passes the emissions test or not.
If it can pass without a cat, then it's OK.
As for benefits - I started a thread on this a couple of weeks back and the general concensus was that there's no real benefit.......................
Up to a certain date it is optional - however after that date it is mandatory that if you car was produced with a cat then it must be tested with a cat.
Depends which MOT station you take it to though - and I know a guy with a F360 with Ģ6k of new straight-through exhaust system which failed his MOT about a week later - at the same place he bought the car and the uprated exhaust system!
__________________ "If you're not producing skidmarks you're not trying hard enough"
I did a custom exhaust about a year ago. I'm running figh flow cats, no resonator. The OEM cats are massive things that I can hardly lift. The high flow cats I'm using are about the size of a small coffee cans and weigh a couple pounds each. Overall I reduced the weight of the whole exhaust I'm guessing 65 lbs or more.
Oh and did I mention the sound is awsome...
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