I am going to install a tri-oval carbon fiber yoshimura full exhaust system on my Busa. The dealer is insisting that i need some block-offs and a Timing retard. I would like to know if these "necessary" items are really necessary[/QUOTE]<span id='postcolor'>
The block off plates that the dealer speaks of are for your PAIR valve. Many folks remove the pair valve when installing aftermarket exhaust because it's basically just 2 lbs of extra weight that's only purpose is to meet emissions requirements, and it's easily accessible when you've got the stock exhaust off.
The pair valve basically add air to the exhaust mixture, which may cause your aftermarket exhaust to pop or backfire. The other option to removing it is to leave it in place and just block off the hose (that feeds into the airbox) and the inlet on the air box. That way if you ever want to go back to stock, it's very simple. If you decide to do this, you won't need the block off plates your dealer spoke of. I'm not overly worried about 2 extra pounds on a bike that makes 165 HP....so I left mine in place and blocked the line.
As far as the Timing Retard Eliminator (TRE), it's without a doubt the best $70 or so dollars you'll ever spend (although you can make the same thing for about $1.50 in parts from Radio Shack- its essentially nothing more than a resistor). This mod is highly beneficial wether your bike is stock or w/ aftermarket exhaust. If you decide to buy the pre-made TRE (Ivan's TRE), it's a "plug 'n play" affair that takes less than 5 minutes to install.
Benefits of the TRE are no more low rpm surging (1st gear lashing), more HP available at lower RPM's and it bypasses the 186 mph limiter on restricted models.
I'd highly recommend that you visit for more information on any mod. It is, without a doubt, the best technical Hayabusa site on the internet and the members there have a wealth of knowledge. Before you ask any questions do a search for the info you're looking for becuase I guarantee someone's already asked the same question.
