rebuilding yzf450 2014-muffler questions

Well ,the season is over and it is time to rebuild the engine (44.5 hrs, remapped per dr Lewis,MX tracks only) Am planning on piston,rings and wrist pin , suspension fluids and clutch plates,chain and sprockets, new brake fluid

When i took the mufler out, i noticed the packing was loose inside the canister so i dis-assembled for a re-pack

i mesured the following inside the muffler:

Exhaust inner perforated tube is 17 inches long,45 MM. Dia

At the end, the perforated tube overlaps over a 4 inches long,31 MM. Dia solid pipe attached to the end cap and that smaller tube continues through the end cap until it reaches atmosphere

Understandbally, this is to mufle the noise and at the same time creates back pressure to the engine

My questions:

1-can i cut off the 4 inches smaller inner tube to reduce back pressure and have a more open exhaust (more top end) (the end cap would still be 31 MM. Dia ) without too much compromise elsewhere in the powerband?

2-the packing was burnt at the end, in the overlapping tube section, where back pressure is maximum , so i expect longer packing Life without this flow restriction and hope the new set-up carries me through a full season (approx 90 hrs) without mid-season rebuild - true ??

There is plenty power on top,and am not planning on after market exhaust pipe but if i can have a freebe (little more top end) i will take it ;-)


I would say cut it back, it will definitely be a bit louder. you might even get a marginal performance gain on the top end. If not it could allways be welded back back on. As far as I know most aftermarket slip ons are straight through without the insert. Let us know what you find.

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