Lighter pulleys help in the unsprung weight on the crank and therefore giving you a small hp gain. There are two types Just a Lighter pulley or A Lighter Undersized pulley with a matching Alternator pulley in which you would also need a smaller belt. NST? Sells this version as a set and also Stillen? Sells the Lighter and Undersized type. You need to decide if its worth the expense and what type would work for you? I've been using the NST lighter undersized type with no problems and I did notice a slight off idle difference.
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