a turbo head c6 an sw7 or an s7. just needs to be a long enough race for the 7 ports to catch it. in my mugens my c6 from a dead start to about 3/4 top end walks away from the seven ports on top end however they catch up but not too quickly. also depends on how you tune it. c6 has a 14 tooth pinion the s7 has a 13