any chance that when you put the drive back on that the spacer was put on the wrong side of the trim rams and you are not getting trimmed in all the way?

Put the beer cooler in the bow, you will plane much easier.....

A good amt of single I/O's won't even get on plane with them open.

Do you have k planes or trim tabs? If not, that will really help your boat get on plane. You are not too far from Hydromotive. They have a wide variety of prop styles in 3,4,5,and 6 blades. Call them and talk to Thom Bucknell. Very knowledgible about props and a honest good man that will work with you and.get your boat propped right.
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I have dual ram bennets there 22in long at least 12in wide i would consider them k planes but not sure i explained it right because it jumps right up on plane so to speak but when u get it right on that transition point of your on plane but not really moving good yet thats when blow out happens so your essentialy just on top when the bow falls down and starts to flatten out right when you would start poiring the coals to her is when this is happening not the act of getting on plane so much as right when the boat tips down to start goin idk 15 mph 20mph 2500- 3000rpm is the crucial moment, its worse when i use the tabs actually, **** at one point it was rough had wife an kid in boat was cruising very slow put the tabs down pretty hard never touched the throttle blew proo off so bad had to set her down and start over and use way less tab, i dont ever need to put a person or weight up front, the trim rams are on right, maybe i need a new prop guy, those holes open i think are not good either but exhaust is goin thru transom so i didnt think it would matter

Thx for the info on hydromotive i will call him, tinkerer i know what you are sayin iam scratchin my head here it should only really be blowin off if i was hittin it hard but iam not any chance just the shear torque difference is the main issue?

If I understand correctly it isn't carrying the bow.

Padraig

Since you are not using the torque, there is no differance. You keep backing off the throttle. I betcha you are using LESS torque to get up than you used to with previous engine. Prop vent holes. You are not running thru prop exhaust. But, is there an exhaust hose between drive and transom assy? You have large low-pressure area in front of prop blades. Could still suck air thru them if that hose is connected. Because as you come up out of the water the exhaust vents in transom shield AND that exhaust passage come out of the water and are exposed to air. And that seems to be when the bad things happen. Maybe get a 4 buck plumbing cap and plug off the drive side of the exhaust passage.

It's not the prop. Something is interfering with it. Regardless of what the indicator says, are you sure the drive is going all the way down? It doesn't take much trim to blow out a prop while planing. Also you said it was getting loose at high speed.

At 8.5 inches deep you don't have anywhere near enough HP to blow the prop out without ventilation.
Either the drive is not trimmed all of the way down or something is ventilating the prop.
Take a picture of the drive all the way down and show the bottom of the boat in the picture so we can get perspective.