I have about 70k into the boat including what I pd. Considering a new 290 is 335k i think I'm keeping her

So from what I see here the xr upper will fail before the xr lower? So get the upper first, i just can't spend 25k on a complete drive right now lol, between my prop and whipple intercooler on the way i am already at 10k this summer.

Unless you pin the throttles to WOT, you have variable tq with the throttle sticks.

Conservative timing is ok, but only by a few degress. Otherwise you're heating up the engine and exh valve with late timing.

Camming it to run way up above 6000 will naturally drop the tq down low...most of the time.

Drives and transmissions are rated in max TQ, not HP. So increasing RPM (more contact of gear teeth per minute) means more strength capacity. Provided the design can handle the higher rpm.

I always prefer to prop lower and get the rpm up.

The roller cam i had built for my 575 should peak at 5600 and carry to 6200, 241- 248 at 50, 650 660 lift on a 114 lobe. Pulling engine soon. Doing afr 315 full cnc, good exhaust valves, cut to 114cc, 8.1 compression. Whipple intercooler and a new blower shop 250 blower. Should be a sweet package and very reliable. Also building a 8.4 compression merlin bl9ck 555, afr 357 with a 248- 255 676 lift on a 115 lobe. This one will be nasty. Still going to run the 250 blower. Will make 875 easy, and be very reliable. I will do the upper drive when I upgrade this 575. Right now the 575 sci will push my velocity 280 around 90 mph with a 29 pitch max 5 prop. Looking for 105 mph or so is my goal.

From my experience it's always at peak torque when the drives fail. Like 4000 RPM with a big engine blower motor going in and out of the water with 5 fat friends on board a single engine performance boat, Bravo drive destroyer!!!

Wow what a difference adding the second ram for steering. 90 mph rock solid, almost zero chine with tabs up.

Running right at 5500 at 90, 11% slip.

Low prop slip is comparable to running slicks on a car. Lots of good traction, but the loads are distributed directly to the gearing and engine.

If you had a hill climb car...pushing it hard aĺl the way up with slick tires, when it hits a slight bump and the tire looses downward pressure...the tire can slip and grab again. This shock loading will translate through the entire drive train...hammering on the weakest link.

Props are no different...if you're tight on the slip, any in/out of water for the prop is shock loading, translating through the gearsets. Heavy flywheels make it worse. The inertia of a 30lb flywheel at 6000 is pretty intense.

The blower will help carry the cam up the rpm band. Often around 400-500rpm. A 250 is smaller for the airflow required for your expected HP, so it may not carry it as far.

depending on your location may want to consider a local person/shop, that way if there are any issues you have a relationship with someone local that is a dealer.

I had a 28' cat with a single 850 blower motor and an IMCO SC drive. I was lucky to get 15 hours out of the upper which is the same as an XR upper in a stronger case. It just keeps finding the weakest link. I even installed a drive guardian. It would shred a gear or break a clutch shaft or a vertical shaft. Upgraded all of the parts with the best I could find and then it would break u-joints. Never ending struggle. Most of this would happen just cruising at 70mph/4000 rpm under max torque situations. the guy I sold it to went with a SCX upper with the SC lower and did get a couple of years before destroying the lower gears. That is what I would recommend.