You can start with one 3/32 hole.
Assuming you do not have a restrictor valve and are pumping straight to pipe, your using the hole as a restrictor. For testing purposes in a 4 banger your looking for ~1/2 gal/min flow. Not exacly sure what your fitting looks like but you'll probably get to 2 holes at 3/32, or one 1/8. You will end up with an exit area ~0.012"-.014".