speaking from first hand experience drive height is absolutely critical to get it to perform, too low and it's going to be a dog. Period. Dragging that giant case through the water is like dragging a boat anchor. I've been there done that and wasted more money then I'd like to talk about. On the transom even with the bottom. If it's on a box I'd set the box so you can go even 1 and 2 above. I've ran my 28 2 below 1below even and 1 above. night and day difference in speed and boat attitude all around. The higher it went the better the boat felt and handled and drastically started to go faster. Planing ability never changed much. 1 above slips a hair more getting up but even in Point pleasant testing Saturday it planed in 4-6s. If I wasn't racing it I think I would fill the transom and try even higher but I feel I'm at the point of diminishing returns.

if you're still planing on racing the boat. (Procharger guys right?) I would also go straight to a crash box. It'll help recoup some of the parasitic loss in the drive. I went the transmission route at first and saw solid gains everywhere by eliminating that.

As far as props my boat planes with pretty much any of them. I would be willing to let you try some that I have in various diameters and pitch assuming you are running a RH drive. I have the some of the smallest pitch big shaft props.

there are many ski race boats here in Australia with #6 behind 1350s, 1650s and custom built turbo motors. Most run a 2 speed powerglide transmission to get some low down launch and then shift gears for high speed

#6 on a 21
 

I was just at the Catalina Ski Race and saw a 21' hull with a Merc 1550 and a PAIR of #6 drives on the back

Check out Aussie ski racing. They run 21' hulls with #6 drives to 120mph sustained down the river while pulling a pair of skiers.

I'll try and post some pics when I get back

Dragging the boat anchor, that’s exactly how my 25 outlaw felt with an imco SCX 2-1/4” below on a 12” ext box. Whippled 509 just didn’t really feel like it had nearly double the 496ho hp that it replaced. So now it looks like Scx-4 is my only option to go higher without transom work. Scx-4 would put me at 1/4” below, on a 12 ext box.

Any ideas on how this might work with a #6 prop? Could I still get bow lift/ trim reaction? Would this be too deep for the scx-4 case and or a #6 prop? I was told planning would be my issue with the scx @ 2-1/4” below but I could jump outta the hole if I wanted to.

It feel would work with a 6 prop. Even at 1/4” below I would bet that it would work with a bravo style propeller in the 5 blade variety. If you choose to run a 6 prop you might need to have the diameter in the 16-16.5” range depending on how the boat feels. I have quite Afew smaller pitch 4 blade 6 props that id be willing to let you try or sell you if they work for you. Obviously it’s a big financial decision to buy a Scx4 on a guess but I think going up is going to gain you speed. It’s Just a matter of do you want to redo the transom or do you want to buy another drive.

Unless Konrad has figured out how to make their drives live I’d stay away from them in high hp applications. I installed a pair of konrads in a center console with twin 480 ta mars and they wouldn’t stay together. If they can’t handle that application there is no way the will live in a high perf application with 1000 hp
if I am not mistaken there are some number 6 drives on some
of the Australian ski race boats. I thing those are under 25’

Talk to pro27 here on the boards, if you haven't already. He has a 27 Progression with a whippled 525 and an SCX4 running a #6 prop. He can probably get you going in the right direction. I believe he's running an extension box too.

I’ve talked with Pro27 a few times and he has been helpful and given me some pointers. Most that I’ve talked to about insist that I should step up to the #6 props otherwise gains could be minimal.

Where are the Australian ski racer x-dimensions or prop shaft in relation to the bottom of there hulls?

Mickeymcclgn
Have you ran your 28 with a #6?
Was it a non stepped or stepped hull? With notch?