What in the world is this suppose to mean. I think it means you have to bore your 400ex over and do a ton of other mods for this exhaust. If i just got:
a vented air box lid, jetted, airfilter, magnum rev box, would it be good?
(curtis sparks x-6 full exhaust)
Sparks Racing has developed an exhaust system for you and your TRX 400EX This system is a piece art, it involves an extreme amount of additional labor to create the maximum performance from the 400EX, but it is worth it. You will love the quick acceleration and incredible peak power.

 

Meaning they put the extra labor into the exhaust to get the max out of it. I almost got that same exhaust until I read the X6exhaust is severe overkill for a basically stock 400 and you would end burning the exhaust valves if put on a stock engine. The X6 is the big core exhaust meant for big bore engines. If it was me I would get their spark advance key, filter, lid, re jet, and another exhaust. But that IS what I did and I'm very happy with the results. Rev boxes do advance the timing and extend the rev limit. But cost about $100+ and the higher rev is useless because your power falls off way before even the stock limiter. The advance key is $20. Get the key and put the extra money saved towards something else.