1299 w/stock header, aftermarket slip-on question

dadams · Jul 28, 2016

The exhaust valve at the outlet of the headers for noise control(?), what's the consensus? Remove it or leave it as is with the spring holding it open? Anyone tested it both ways with dyno charts showing the differences? Personally I see it as an obstruction that should be removed.

ilmostro · Jul 28, 2016

I feel the flapper deactivated and the flap on the full open position will equally split the exhaust gasses to distribute the gasses perfectly between the left and right muffler/can.

All jokes aside, I have my servo motor and cable removed on mine with safety wire holding the flap in the open position. I have the forward exit Termignoni Evo slip-ons and the bike works beautifully.

I've experienced in the high revs where the flapper closed due to the exhaust pressure and the bike felt like it hit the fuel cutoff. The reason why I have the flapper safety wired. I might try and cut the flapper out and plug the hole or I'll get the itch to spend on the bike and get the titanium manifold made for the Termi evo slip-on.

Thamer · Jul 28, 2016

Can you show where you safety wired it? Thanks.

royal · Jul 29, 2016

Mine just has it held open.

wrussi · Jul 29, 2016

i have my cable removed but the assembly is still in there.. i dont see how high exhaust pressure can cause the valve to close.. the spring is pretty strong holding it open. how do you know what you feel its caused by the valve?

ilmostro · Jul 29, 2016

wrussi said:
i have my cable removed but the assembly is still in there.. i dont see how high exhaust pressure can cause the valve to close.. the spring is pretty strong holding it open. how do you know what you feel its caused by the valve?

Maybe the spring on my exhaust flapper has less tension from the factory, but ever since I had it safety wired open I haven't experienced the issue.

I felt it was cheap insurance to wire it open. I had it happen twice beforehand and I decided to take the advice from 80Shilling to wire it open.

The force to close the flapper by hand is pretty easy. Also, the cable adds to the spring's tension to keep the flapper open. Once the cable is eliminated, there is less force to keep it open only with the spring.

Another factor that might play into the velocity of exhaust gasses is OEM catted cans versus aftermarket.

kismetcapitan · Jul 30, 2016

I didn't run into the flapper valve closing problem until I put the Termi Evo front-exit slip-ons on. mine is welded open. I was going to remove the flap, but I'm either going to do the Termi headers (I haven't yet since I haven't been able to confirm the part number that matches the front exit Termi cans)....or find the high-mount dual exit Akrapovic WSBK exhaust. SBK homologation rules require all parts be available for sale at somewhat "reasonable" prices. If I come across that exhaust for sale, unless it's more than $10k, I doubt I'll be able to resist buying it.

1299 w/stock header, aftermarket slip-on question

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