RE: Vibrations after replacing the cat/silencer

[emax_1]

RE: Vibrations after replacing the cat/silencer

I've replaced the cat and silencer on my 04 GS. However, my idle has creeped up to around 1300/1400 rpms. I also notice more vibration throughout the rpm range. I haven't done a TB sinc yet because I wanted to see if the O2 sensor would work it out. After a 130 mile run yesterday, I'm ready to take a look at the TB. My question is wether this is typical on these oilheads when you take off the cat and silencer? I have replaced it all with a Neptune Y pipe and silencer which is very nice quality from the land down under. (Also posted on BMW Sport Touring)

Thanks,

Steve Maxwell
Marion, Illinois

 

[pffog]

Should not effect the idle that much, or the vibes. My guess is you unseated one of the cables at the throttle bodies or splitter, so it is holding the throttle plate open slightly and totally un-synced them as well.

 

[emax_1]

Re:

Thanks, I checked that once and I'll check it again

 

[j-budimlya]

I have witnessed the same thing when replacing the exhaust system, especially when removing the cat. converter. I believe that it is related to "better" breathing of the motor and that better breathing(reduced backpressure) causes a pronounced increase in any difference between the cylinders. This increased vibration can me minimized by a very careful valve adjustment and /TB sync, but from my experience it will return faster as soon as the balance is thrown off by valve opening or TB opening differences. The motor does breath better and improve acceleration, etc.; but I found the frequency of crusing vibration increase undesirable and for this reason I went back to the stock exhaust system. Low vibration trumped the small increase in power for me.

I have to add that I am a very careful engine tuner and I like a very smooth engine with minimium vibration.....and of course I am a IBA long distant rider and do not try to race the local rockets very often.

I suspect that some folks accept the increased vibration and could care less...they prefer more exhaust noise and power.

Hope that this helps with your decision.

 

[emax_1]

Trade off

Thanks. I was aware of much of the tradeoff prior to my swap. I have achieved the major goal of a little more power at highway speeds. Last summer I swapped the TB intake tubes for the larger version and got a boost at 70+ mph for passing the big rigs. I, too, tuned the bike for smoothness at and above 4000 rpms. I'm sure I'll work things out with the new setup.

 

[emax_1]

Re: Vibrations

I spent some time today syncing the throttle bodies. After a 40 mile ride I'm pleased that I now have a good idle speed and pretty well balanced set of TBs.