Don't know the transportation laws around your way, but pretty sure that will be illegal (exhaust gas venting under the car) not to mention the outrageous noise and resonance you will get. A muffled flat 4 sounds like an angel farting, it's a thing of beauty, a non muffled flat 4 however .........well it will sound like you have a whole in your exhaust, which is exactly what you will be doing. Just my opinion, it's your car and ears.
Old fogie's opinion: Besides making the exhaust note sound cool (annoying), what are the benefits of this mod? Increased airflow does not equal increased performance unless the ECU has been reprogrammed to know what to do with the air. Running richer doesn't automatically mean running faster. In fact, making any mod to the airflow and fuel ratio mixture will more likely reduce performance.
It reminds me of when we were kids and we would use clothes pins (Google them) to attach playing cards (Google them) to the forks of out bikes so they flap against the spokes and sound like a motorcycle. It sounded cool but ultimately slowed the bike down. So, you want to sound like a boy racer without all of the money or performance?
Just get a huge sub-woofer. That way you can still piss off your neighbors and at least have a sound that is useful. Old man out - drops mike.
Didn't know what this was until some Google time was spent on it. First off, the original implementation appears to have been to insert the washers between the rearmost section which included the muffler and the next pipe up, normally connected to the rear cat and resonator - so its not in a place where its likely to kill you. In the case of Gen. 2 OBs like my own, the gasket at that location likes to leak anyway, and I haven't heard of it causing a driver to die of carbon monoxide whilst driving along happily. Secondly, and specifically in response to DavePeab, the change of removing the muffler entirely is certainly not enough to be outside the envelope of the stock ECU map to work with. I find all this discussion of NA (naturally aspirated, in case anyone didn't know) motors needing an ECU remap for the relatively minor flow work of intake and exhaust to have ANY effect laughable. If that little change were enough to warrant a remap, Subaru would have dead motors being replaced because of the amount of people that run with super-dirty air filters and rust plugged mufflers.
This 'hogzaust' looks largely pointless, apart from maybe wanting to know what your car would sound like with just a slightly less restrictive muffler. As a test for that, seems like a cheap way to know what you'll probably get. Got some spare washers and a 20 mins to waste? Give it a whirl.
I wasn't afraid of any damage to the engine or other components. One of the Google threads I read mentioned putting the washers on at the manifold. That'd screw up the ECU's ability to compensate. My point was, not only will it NOT improve performance, but may very well DECREASE performance. The guys with "Rice Rockets" around here put 6" exhaust pipes and KNB filters on their cars hoping to improve their horse power. But doing so without an ECU adjustment doesn't increase horse power. I was confused by the Google post and hope I didn't scare anyone away from this simple modification that will make your car sound cooler. But please don't do it in my neck of the woods. The rice rocket boys are annoying enough already. ;-)