s13 are a 240*/248* variation, which is why people like to use two s13 exhaust cams for the double 248* setup, plus it's cheap and opens up the top end just a tad.
that sounds right. my set up worked great for me, lots of autocrosses in SM class with advan A032s against mustangs and what not with full slicks and i was in the top three most events. the extra power helped compared to the stock ka with exhaust before. it opened up real good on VIR too.