Performance Mods: Mazda 6 L5 2.5L block, Ohlin Coil Overs, Racing Beat Header, 17x9 wheels and 4.1 Diff. The head, induction, and brakes are standard NC. Running Road 180 Treadwear rubber (NA08s) so had to lift in some places to stay on the track.
The Mazda 6 L5 Block gives me a little more HP at the wheels (164) and a lot more torque. On the down side I loose 1000 RPM as there is nothing after 6000 RPM.
Looks like 500cc goes a long way.
http://mx5cartalk.com/forum/viewtopic.php?f=68&t=52306 Reading about it makes me feel like giving up the NA for a NC...