Just switched from scx upper/bravo xr lower to a scx upper/imco sc lower and having planing issues. Prop starts to ventilate at 3k right when boat wants to roll over. Used to plane without tabs, now even dropping tabs I’m struggling. Same props same everything. Anyone have any insight?

Different design cavitation plate ?

Nope. Literally the only change is the lower

Maybe try something like Max Machine works add on plates ? If they makem for those drives. Have had good reviews here and elsewhere.

Think I figured out the problem. Now do I want to.chase it? The scx upper xr lower combo basically had a double cav plate. And the space between prop and plate were pretty tight. Now I have a big gap with just the upper cav plate. So chase it with a bigger diameter prop? Max machine wedge? Or scrap it and go back to a xr lower.

what happened to your other thread about this issue

Mixed terms here. Cavitation is the prop boiling water due to low pressure on the side of the blade causing loss efficiency and pitting of the prop. Ventilation is the props sucking in air from surfacing. Those plates on drives are ventilation plates but I guess people interchange the terms.

Changing your lower unit probably raised the X-Dimension of the prop shaft height and now you are surfacing the prop perhaps? Adding a spacer to drive the prop lower?

No still at 4.5"

Well I bought the max worx Batwing. See what happens. He is pretty sure it will do what I need. If that doesn't work, then I'll.have a new sc lower for sale lol.

Curious to see how that works out for you
Post results. Hope it works for you.