I found a fully boxless system lost most of the power and torque throughout the rev range. Yes the revs do rise quicker but you are not going anywhere far soon. There is a need for a little restriction in an n/a exhaust system especially in one as low powered as us n/a starlets. I did a lot of reading up beforehand on pros/cons and also gained some valuable info and experience from watching my zorst getting done and also asking them stuff and making sure I got what I wanted done. No way would I leave them to it. The term is 'exhaust scavenging', exhaust gasses need time to scavenge in order to make useable power, if they just being farted out as soon as possible they have no time to do this scavenging hence the lost of backpressure, altho backpressure is an overused term in itself. So its best im my opinion to leave at least one restrictive box in there be it the cat or one centrebox. By all means experiment, I know the majority of people will want to decat more than anything, try a decat and take all boxes out, see how it goes, if it runs like crap as it should do, get a centrebox added which wont be difficult or expensive. You could even tell the zorst place to still include a centrebox in your package or use your old centrebox, but just say you want to try it out boxless, and if its not good then come back for a centrebox. This is what I did and returned to the zorst place the very next morning as it was waaaay to loud and also it ran like crap as there was next to no torque anywhere. I would like to say that my exhaust system is a lot more freeflowing than others so I felt the loss of torque and backpressure much more severely, the addition of a centrebox changed this. The more freeflowing an n/a exhaust is, the louder it will become. I hope my experiences help a few people out. Let us know the progress with your decat Ross and whether you got any noticeable gains out of it. Give it a little more time. Moved to technical for further discussion. Joz