Agreed, a 2.5 or even 60mm is good on H22a, 3inch if u want more top end power, heck ive got a 2.5 on my d16, the difference in top end compared to oem is noticeable! Low end suffers, but not to the degree where its un-drivable, everyone says not to run a 2.5 obviously never had a 2.5 system on there 1.6! freakin sheeps LOL