My vote is for the v-spec. There are faster engines for different tracks but the v-spec seems to run quiet well up against anything else.

economy, my novarossi s421b seemed very economical to me, my v-spec is alot better then that. We recently ran a 30 minute race and the v-specs i believe were the only engines doing two stops. I put the smallest carby restricter in, as an experiment, and got run times of 14 minutes (no it wasn't lean) it did take away a fair bit of power though.