I've been looking all over for more information on this engine to find out how similar it is to the Mazda2 (Demio) 1.5L. What I learned is there are a few differences.
Since USA uses different octane ratings and 87 octane is slightly lower than other countries, the scion iA uses 11:1 compression ratio instead of 12:1 in Japan, Europe, and some other markets. This represents a 2-3% power, torque, and fuel efficiency reduction.
The iA does not use the same 4-2-1 header as the Japanese demio, I believe it uses a 4-1 header instead. Although I haven't been able to find verifiable data to back this up. 4-1 is more compact, allowing for more interior volume since the firewall can be pushed forward and lower by a few inches. The difference is that 4-2-1 allows exhaust heat to leave the cylinder head much faster which is one other reason for the 11:1 compression ratio. But by using the 4-1 design it allows Scion to increase rear passenger room by 2" or more.
The last thing I have found is that the engine uses the Miller cycle, which is used to mimic the Atkinson cycle during idle and low load operating conditions. When the engine operates in high loads it will use a traditional Otto cycle for extra power.
If anyone knows more about the iA engine please let me know because I am really curious to see what exactly is changed. It definitely explains why the iA only makes 106hp and 103 torque compared to the Demio's 115hp and 109 torque.
