Flow Restrictor In Crossover Pipe

[Scott LaCosse]

My bike began making a very loud metal on metal clanking sound in the area of the exhaust crossover pipe that connects the two headers. Turns out there is a flow restrictor in the pipe that had come loose. The restrictor looks like a washer the same diameter as the pipe with a hole in the center - apparently to restrict flow between the left and right pipes.

The dealer has said they will replace the affected pipe under warranty, which would restore the exhaust system to its factory "restricted" state. They put the pipes back on so I could use it pending arrival of the replacement parts.

Here's the question: They suggested I may want to leave the bike as it is - with the restrictor out. I talked to two different people in the dealer's repair shop about possible effects of this. One said he didn't know, the other claimed that only an increase in noise would result. I've ridden the bike and can't notice any significant difference in noise or power. Has anyone had any experience in this regard? I'm also curious as to any speculation you all might offer as to long term implications of leaving this part the factory thought was needed out of the system.


[This message has been edited by Scott LaCosse (edited 11-07-2000).]

[Pete May]

The 'restrictor' in the link pipe will have minor affects on torque and exhaust noise, I would suggest better in than out, as it must have a cost, and BMW would not fit it if it was better left out.

[roger albert]

Hi,

Either way, the differences are virtually guaranteed to be subtle. I'd be tempted to get if fixed under warrantly, but would be very unlikely to spring for it post warranty on my own budget. It will likely improve breathing at one small rpm range (or several) and hurt at others. Its a tweaker, not a major curve shifter. You'd in all liklihood need a couple of identical condition dyno runs to see the effect at all. Virtually no chance of feeling it by the seat of the pants
(which means your subjective observation has been pretty good so far) I wouldn't worry to much either way. If the dealer fix is convenient for you, let them do it. If its a big hassle, I'd leave it out.

later
roger