SILENCED DE CAT if you value your sanity and ever wish to drive it on the street again. While it doesn't make it much less bad but least not so loud. But good thing with just the straight pipe is fire balls. Depending on the rpms/gas you use you'll be able to shoot yellow, blue and sometimes white fireballs.
I had the Larini straight de-cat with a Stage II and it was loud (like 107 dBA in-car at WOT). :evil: Honestly, it was about a 3 dB difference from when the cat was on. However, if the track you run on has draconian noise restrictions, I'd go with the silenced one - although I can't attest to the difference.
The "raw gas" smell reminded my of youth, where I'd spend time in my Dad's garage gratefully inhaling the smell of MOPAR V8s back before environmental controls.
Uh, that might explain some things......
I have a de-cat to an arqray dual chamber. It sounds mean but, it does smell a bit. My CEL came on after 100 miles. I'm in the process of sending it to Charlie to a reflash --- sounds like he's the man when it comes to Loti !!