exhaust tightness question

My SW-T400 is a bit noisy at higher RPM, it got better since I fixed the muffler seal clamp right.
Today just for fun on a cold bike I pressed both hands to seal both exhaust pipes.
There was no reaction in idle rpm or sound,ther was also no real pressure against the palms.
That really puzzled me.

Can somebody shed some light what is going on?

I KNOW THERE IS A LITTLE BLOW BACK BECAUSE OF A NOT TO FRESH EXHAUST SEAL ANYMORE (dam caps lock). But this it is as if there was a bypass.

I wish you hadn't mentioned the lack of pressure build up on the exhaust system. I just checked my '08 and it's the same. No pressure build up at the two outlets. I'll have to look it over eventually. Might be leaking where the exhaust goes into the muffler. But I couldn't hear any leaks and it didn't effect the engine idle at all either.

when I look at a 2002 600 or 2009 400 the exhaust system is except for the pipe diameter and seal size pretty much the same.
When you look at part nr 6 it looks like the exhaust pipes we tried to block while the exhaust has a set of extra little pipes connecting (maybe loosely for cooling purposes) with this part.
Maybe to keep it cooler there is a gap between the nr 6 pipes and the exhaust pipes.

https://www.bike-parts-honda.de/honda-motorrad/600-SCOOTER/SILVERWING/2002/FJS6002/Chassis/ABGAS-SCHALLDAEMPFER/13MCT1E1/F__2400/2/5356

4 screws solved the riddle
The exhaust gasses are cooled by air what is suckt with the exhaust gasses between the exhaust inner tube and the air cooling outer tube what gets the air from the gap behind the silver end cap.
So to block the exhaust a bit to see if it is intact, you need 2 corks from a sparkling wine bottle what fit through the big diameter but not the small diameter tube.

The packing as the Japanese call it (gasket) between exhaust pipe and muffler needs to be replaced now and then----I always carried a spare.

A cool design .

Without that outer cooling tube that nice plastic muffler end cap would get very hot and melt. Cooling design at it's best.

Since my SW is a rather beat up used bike, it's muffler guard was scraped up. New ones were expensive. I decided to replace the muffler with a Delkevic slip on. It's a bit louder but not intrusive. Anyways Honda always had a great design but God awful heavy. I do not miss the factory muffler at all. The performance gain is mostly due to weight savings. It does seem a bit livlier however. I would have loved to see a lighter factory muffler. The new one slipped on with a little RTV.