as a general rule you could say the more moddd the engine the bigger the turbo you can use. i have experience with 1, soon to be 2 and in the process of building a highly modded and stupidly expensive 1500. these have a progression of turbo size. slightly modded a14 with a turbo of a ca18, or stock would be good, what i now have is off pulsar gtir, signifcantly bigger. we will see how it is suited next week. the highly modded motor is getting something like the garrett disco potatoe with the smaller a/r of .64. this is 6 months away. i think if you look at the smaller ones you are going to be in the ball park. the ca18 turbo is on full boost (13-14psi) at about 3100rpm. less boost will come on earlier.