checked the keyways there too and everything checks out. We're trying smaller blower pulleys next with the thought that the motor is eating up all the boost the blowers are producing. The fact that the boost went totally away and went to a vacuum as we increased engine rpm kinda points that way. Hoping to increase the boost at the same engine rpm with smaller pulleys is the answer. Fingers crossed!

I had to go down one size on the pulley on mine earlier this year. Wasnt producing as much boost. You should see a noticeable difference with the pulley change. I saw a 3 PSI jump with mine at WOT, also came into boost a little earlier which actually helped me plane out better. Curious to see if this fixes your issue!

Everything was fine in boat for a few years until onecengine’s boost faded away, so you just did top ends redone right ? Vslve jobs/springs probably. Anything else ? And you said they hit thedyno too. Issues only when in boat. So, if this ‘fixes’ them, I would not understand.

Could the blower belt/s be contaminated with oil, fuel, p/s fluid, cleaning/detailing products, etc?

Brand new belts.

Any update on this?

Crazy question, is the Drive pulley actually turning the impeller on the SC in question? or turning under load ( implying possible internal damage of the SC).

Thinking out loud, if it's not compressing, it's working as an air block as the engine is after more than it can draw through the system = no boost and drop in RPM's

So here's an update but still no fix. Decided to pull one of the motors and run it back on the dyno. Motor ran fine - 950 hp and 1000 ft lbs of torque. Put the motor back in the boat and its doing exactly the same thing - 4000 rpm max and showing no boost. This is really frustrating. Boat always ran great.

In what condition was the engine on the dyno, full marine trim?

What is different between dyno and in the boat, Fuel system? Ignition system? Exhaust?
Cooling water?

The problem lies in the differences somewhere?
Ryan

we actually ran it out of a bucket of fuel on the dyno to eliminate a fuel supply issue. Using boats ignition system and supply water pump. Only real difference is the exhaust system using the dynos headers.