I just picked up my new A15 race motor last night and as the owner of numerous A 12's and a daily driver of an A14 this will be my best motor yet. It was built by JTS in Sydney and I'd regard Jeff as the premium A series builder in Australia. On my Weber 40's this is a 140HP motor with a 9500 rpm redline. With Jeffs max head work and 45's it will generate 160HP. When I picked up the motor I spent some time looking over a 200HP 50mm trumpet injected A15 in the best race coupe I have ever seen. So I guess that answers the race engine question A12, A14 or A15 - it's the A15 and it'll still rev enough to scare you. In standard form I'd reckon the A14 will have the edge - it's got the most HP and revs higher than the A12 or A15. In standard form the A15 is a torquey van/ute/forklift motor and the A12 is a great power plant but the lower redline and 200cc smaller displacement hurt it against the A14.