While topspeed isnt a true dual, it makes up for that by italizing the scavaging effect of the engine better.
its really down to budget. if i had the money, i would go FI, but with a budget in mind it would be top speed without a doubt. they are the best low end exhaust u can buy probably (other than cnt
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FI looks FANTASTIC and sounds great. but from the videos i have seen online, the topspeed sound really good too.