What size injector is best for a given combo seems to depend on who you talk to. You would think that it's an exact science, but apparently not. I don't know why, since there is a formula (I forget off-hand) that can tell you what size injector is best for a given combo. With this in mind it seems pretty cut and dried.
I'm building a normally aspirated 331 stroker and depending on who I talk to I'll get recommendations of either 24# injectors or 30# injectors. Some say that the 24's are plenty and that the 30's are overkill, while others say that the 24's won't be enough and the 30's are just right. Who knows.
What I plan on doing is running the 24's and get the car on a dyno as soon as I can. If it falls flat on its face because it's running out of injector, then obviously I'll upgrade to the 30's. But that's just me.
IMHO, don't waste your time worrying about an exact size as you can add or subtract fuel by playing with your fuel pressure enough to take care of small descrepencies in size. Don't try and run a 24 pounder when you need 50's, but if your combo is maximized with a 50lber at 40psi, then a 36lber at 65 or so will work alright. If you have a tuner, you can also adjust the pulse width to do the same thing, to some degree.
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