Well, realizing that youll do it anyway let me make your experience safer. Grapefruit does increase effects from adderall. If you have a full belly or snort your adderall it does little. Empty stomach plus a couple cups of grapefruit will raise effects if you snort a larger dose cause theres enough drip swallowed to be effective.
Really the only real good drinking grapefruit does is if you dont have much in your stomach oral use will be the only worthwhile way, but if a large amount is taken nasally you respond quicker so you can control and feel whats going on before you reach your limit, as with oral you dont know what to do untill you either take too much or lose efficiency if you need more.
Ide advise you to just let a small meal settle and pop your addy like normal, or if you snort crush your normal dose and slowly do your lines, not good for your nasal or lung health but its the best way to control the effects as youll know if you do too much before you really cross the line. Though if you have heart issues youre in danger at any dose.
Do your stuff without potentiating as its not very predictable. If you get too tolerant a few days of half or no use will be enough to boost your effects per dose.