On a 500efi with the 100hp kit, dart pro 1 325 heads and isky cam 244/252 .630 lift and the tune that went with it. The motor still has the stock throttle body. Is there any sizeable gain to the monoblade. Will a tune be needed as it was tuned for the current upgrades.

At 600 hp the tb is going to be a bout a `10 to `12 hp/ft lb tq difference. The stock FA or any poorly designed aftermarket FA will be a HUGE restriction too fwiw, Smitty

What FA do you recommend. I believe its a K&N clamp on currently.

The 525 FA has a pretty low restriction BUT never come up for sale used , plus i think Merc has them over 900$ these days new and you either need to swap a 525 tb on and remote mount your iac to use it or mod the monoblade you buy for it to bolt on. I have never tested the fancy billet one that CP sells, it resembles a 525 FA. The AZSM thats rectangle works ok, in recent testing I want to say a 500 I dynoed in the low 570s dropped to low 550s putting stock on, dropped 4hp or so putting the AZSM on fwiw, Smitty