are 42.5s enough for a PT61

You will run out of fuel, go with the 55# injectors or to be better off go even higher.
 
Its not necessarily the turbo size, but how you're going to use it. :)

42lb injectors are enough fuel for mid 11's @ ~117mph on race fuel (I'm sure some have gone faster), regardless of turbo size.

However, the 61 would easily need more fuel if you crank the boost up and want to go even faster.

For injectors, 50's, 55's, and 60's would all work if you want to be safer. These days I would probably skip over the 50's and go to the hi-z 55's or 60's.
 
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